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10 CX Yearbook of 
11/04 Astronomy 

Editor J. G. PORTER ' Associate Editor PATRICK MOORE 





Associate Editor 



Eyre & Spottiswoode 


First published in 1963 

© 1963 by Eyre & Spottiswoode (Publishers) Ltd 

Printed in Great Britain by 

W. & J. Mackay & Co Ltd, Chatham 


Preface • vii 

Notes on the Star Charts • 1 

The Star Charts • 4-29 

The Planets in 1964 • 30 

Phases of the Moon, 1964 • 31 

The Planets and the Ecliptic • 32 

Notes on the Planets in the monthly diagrams • 33 

Monthly Notes, with diagrams of planetary orbits • 36-71 

Eclipses, 1964 • 72 

Occultations • 73 

Comets in 1964 • 73 

Meteors • 75 

Minor Planets in 1964 • 76 

Some Events of 1965 • 77 


The Distance of the Sun • J. G. Porter • 78 

With Mariner 2 to Venus • H. G. Miles ■ 83 

Selenology - or Geology Applied to the Moon • 
Peter J. Cattermole ■ 92 

The Great Red Spot on Jupiter • W. E. Fox ■ 100 


Telescope Mountings ■ Henry Wildey • 107 

Astronomy and Navigation • Henry Brinton * 1 15 

The Surface of Saturn • H. N. D. Wright ■ 123 

Planetary Nebulae • Colin A. Ronan • 132 

Harrison, Maskelyne and the Longitude Problem • 
P. S. Laurie ■ 138 

The Short-period Comets • J. G. Porter ■ 146 

Recent Advances in Astronomy • Patrick Moore • 158 

Some Recommended Books • 165 

Astronomical Societies • 170 

Glossary of Astronomical Terms • 175 

Some Interesting Telescopic Objects • 198 

Biographical Notes on Contributors • 214 


This issue of the Yearbook of Astronomy follows the arrangement 
adopted last year. The year 1964 promises to be full of interest 
from the astronomical point of view - indeed, all the physical 
sciences may well be involved. The achievement of a U.S. team of 
space scientists in sending an interplanetary probe to the planet 
Venus is likely to be followed at the end of 1964 by the launching 
of another Mariner to the planet Mars, and this, if successful, 
should solve some of the problems that make this planet so 
interesting, as well as presenting us with others as yet unknown. 
At the other extreme, many scientific societies will be celebrating 
the fourth centenary of the birth of Galileo, who is justly regarded 
as one of the founders of modern science. In these four hundred 
years astronomy has undergone many changes, particularly in its 
methods, while the focus of interest has shifted from the solar 
system to the distant nebulae, from the mere cataloguing of posi- 
tions to the application of the laws of physics to the formation and 
constitution of the stars. It is most interesting to notice how the 
modern space sciences have once again directed attention to 
the problems of the solar system. The articles which follow the 
monthly notes cover some of these topics, while there are also 
practical articles on telescope mountings and on the art of naviga- 
tion. It is just two hundred years since Harrison solved the 
problem of navigation with his marine chronometer, and Mr 
Laurie's unique knowledge of the history of the Royal Observa- 
tory is well displayed in his article on Harrison's work. The latest 
results of the space scientists in their study of Venus are also 
described, and although these must not be regarded as final, they 
do at least show that there is still quite a lot to be learned about 
the solar system. 

New readers will find that all the information in this Yearbook 


is given in descriptive or diagrammatic form; the position of the 
planets may easily be found on the specially designed star charts, 
while the monthly notes describe the movements of the planets, 
and give details of other astronomical phenomena that may be 
observed from these latitudes. The reader who needs more 
detailed information will find Norton's Star Atlas (Gall and Inglis, 
175. 6d.) invaluable, while more precise positions of the planets 
and their satellites, together with predictions of occultations, 
meteor showers and periodic comets may be found in the Hand- 
book of the British Astronomical Association. A somewhat 
similar publication is the Observer's Handbook of the Royal 
Astronomical Society of Canada, and American readers will also 
find details of forthcoming events given from time to time in the 
pages of the monthly Sky and Telescope; this magazine also 
publishes complete details of all occultations visible in North 

Throughout this volume time is expressed in Greenwich Mean 
Time; that is, Summer Time is ignored, and the 24-hour clock is 
used, the day beginning at midnight. The star charts are drawn, 
and the notes are, in general, designed for use in latitude 52 
degrees north, but may be used without alteration throughout the 
British Isles, and (except in the case of eclipses and occultations) 
in other countries of similar north latitude. 

Notes on the Star Charts 

The stars, together with the Sun, Moon and planets, seem to be 
set on the surface of the celestial sphere, which appears to rotate 
about the Earth from east to west. Since it is impossible to repre- 
sent a curved surface accurately on a plane, any kind of star map 
is bound to contain some form of distortion. But it is well known 
that the eye can endure some kinds of distortion better than others, 
and it is particularly true that the eye is most sensitive to devia- 
tions from the vertical and horizontal. For this reason the star 
charts given in this volume on pages 4 to 27 have been designed 
to give a true representation of vertical and horizontal lines, 
whatever may be the resulting distortion in the shape of a constel- 
lation figure. It will be found that the amount of distortion is, in 
general, quite small, and is only obvious in the case of large 
constellations such as Leo and Pegasus, when these appear at the 
top of the charts, and so are drawn out sideways. 

The charts show all stars down to the fourth magnitude, 
together with a number of fainter stars which are necessary to 
define the shape of a constellation. There is no standard system 
for representing the outlines of the constellations, and triangles 
and other simple figures have been used to give outlines which are 
easy to follow with the naked eye. The names of the constellations 
are given, together with the proper names of the brighter stars. 
The apparent magnitudes of the stars are indicated roughly by 
using four different sizes of dots, the larger dots representing the 
brighter stars. 

There are four such charts at each opening, and these give a 
complete coverage of the sky up to an altitude of 62| degrees ; 
there are twelve such sets to cover the entire year. The upper two 
charts show the southern sky, south being at the centre; the 
coverage is 200 degrees in azimuth, from a little north of east 


(top left) to a little north of west (top right). The two lower charts 
show the northern sky, from a little south of west (lower left) to a 
little south of east (lower right). There is thus an overlap east 
and west. 

The charts have been drawn for a latitude of 52 degrees, but 
may be taken without appreciable error to apply to all parts of the 
British Isles. They will also be equally suitable for any other part 
of the world having a north latitude of about 52 degrees - e.g. 
parts of Europe and Asia, and Canada. In such cases the times 
given must be taken as local time, and not G.M.T., which applies 
only to the British Isles. 

Because the sidereal day is shorter than the solar day, the stars 
appear to rise and set about four minutes earlier each day, which 
amounts to two hours in a month. Hence the twelve sets of charts 
are sufficient to give the appearance of the sky throughout the 
day at intervals of two hours, or at the same time of night at 
monthly intervals throughout the year. The actual range of dates 
and times when the stars on the charts are visible is indicated at 
the top of each page. This information is summarized in the 
following table, which gives the number of the star chart to be 
used for any given month and time. 

G.M.T. 16* 18 h 2(P -22 h <P 2 h 4 11 6»» 


















































































The charts are drawn to scale, and estimates of altitude and 
azimuth may be made from them. These values will necessarily be 
mere approximations, since no observer will be exactly on the 
meridian of Greenwich at 52 degrees latitude, but they will 
generally serve for the identification of stars and planets. The 
horizontal measurements, marked at every ten degrees, give the 
azimuths (or true bearings) measured from the north round 
through east (90 degrees), south (180 degrees), and west (270 de- 
grees). The vertical measurements, similarly marked, give the 
altitudes of the stars up to 62 \ degrees. 

The ecliptic is drawn as a broken line on which the longitude is 
marked at every ten degrees ; the positions of the planets at any 
time are then easily found by reference to the table immediately 
following the star charts on page 30. 

There is a curious illusion that stars at an altitude of 60 degrees 
or more are actually overhead, and the beginner may often feel 
that he is leaning over backwards in trying to see them. These 
high-altitude stars, being nearer the pole, move more slowly 
across the sky, and a different kind of map may therefore be used. 
These overhead stars are given separately on pages 28 and 29, the 
entire year being covered at one opening. Each of the four maps 
shows the overhead stars at times which correspond to those of 
three of the main star charts. The position of the zenith in latitude 
52 degrees is indicated by a cross, and this cross also marks the 
centre of a circle which is 35 degrees from the zenith, and which 
therefore indicates an altitude of 55 degrees; there is thus a small 
overlap with the main charts. 

The broken line leading from north to south is numbered to 
indicate the corresponding main chart. Thus on page 28, the N-S 
line numbered 6 is to be regarded as an extension of the S line of 
chart 6 on pages 14 and 15, and at the top of these pages are given 
dates and times which are appropriate. 

The scale is the same on all the charts (approximately 25 de- 
grees to the inch), but the overhead stars are plotted as a true map 
on a conical projection, and are not simple graphs like the main 



October 6 at 5 h October 21 at 4 h 

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Overhead stars 


The Planets in 1964 





















































































i so- 























June 19 

Feb. 17 

Apr. 22 

Feb. 15 

Sept. 2 


Opposition: — (1965 Mar.) Nov. 13 Aug. 24 Feb. 27 May 7 



Mercury moves so quickly among the stars that it is not possible 
to indicate its position on the star charts at a convenient interval. 
The monthly notes must be consulted for the best times at which 
this planet may be seen. 

The positions of the other planets are given in the table on the 
opposite page. This gives the apparent longitudes on dates which 
correspond to those of the star charts, and the position of the 
planet may at once be found near the ecliptic at the given longi- 

Examples : 

(1) What is the bright planet seen to the right of the Pleiades at 
1 a.m. (Summer Time) on September 12 ? 

The time is h G.M.T., and from the table on page 2 the 
appropriate star chart is found to be number 10. The 
upper chart on page 22 (10L) shows the Pleiades, and the 
planet is seen to have a longitude of about 55 degrees. It 
is then identified from the table opposite as Jupiter. 

(2) Where can Mars be found at the end of October ? 

From the table opposite we see that Mars does not come 
to opposition until 1965, so that it is still a morning star. 
The same table gives its longitude as about 147 degrees. 
Using charts 12L or 1L, it is seen that Mars is then near 
the star Regulus, rising in the east an hour or two after 
midnight, and well up in the eastern sky just before dawn. 

Phases of the Moon, 1964 

New Moon 

First Quarter 

Full Moon 

Last Quarter 
j i. 










Jan. 6 

n in 
15 58 

Jan. 14 



Jan. 22 



Jan. 28 



Feb. 5 

12 42 

Feb. 13 



Feb. 20 



Feb. 27 



Mar. 6 

10 00 

Mar. 14 



Mar. 20 



Mar. 28 



Apr. 5 

05 45 

Apr. 12 



Apr. 19 



Apr. 26 



May 4 

22 20 

May 11 



May 18 



May 26 



June 3 

11 07 

June 10 



June 16 



June 25 



July 2 

20 31 

July 9 



July 16 



July 24 



Aug. 1 

03 29 

Aug. 7 



Aug. 15 



Aug. 23 



Aug. 30 

09 15 

Sept. 6 



Sept. 13 



Sept. 21 



Sept. 28 

15 01 

Oct. 5 



Oct. 13 



Oct. 21 



Oct. 27 

21 59 

Nov. 4 



Nov. 12 



Nov. 19 



Nov. 26 

07 10 

Dec. 4 



Dec. 12 



Dec. 19 



Dec. 25 

19 27 

Reproduced from the Nautical Almanac by permission of the Controller of H.M. Stationery 


The Planets and the Ecliptic 

The paths of the planets about the Sun all lie close to the plane of 
the ecliptic, which is marked for us in the sky by the apparent 
path of the Sun among the stars, and is shown on the star charts 
by a broken line. The Moon and planets will always be found close 
to this line, never departing from it by more than about 7 degrees. 
Thus the planets are most favourably placed for observation when 
the ecliptic is well displayed, and this means that it should be as 
high in the sky as possible. This avoids the difficulty of finding a 
clear horizon, and also overcomes the problem of atmospheric 
absorption, which greatly reduces the light of the stars. Thus a star 
at an altitude of 10 degrees suffers a loss of 60 per cent of its light, 
which corresponds to a whole magnitude; at an altitude of only 
4 degrees, the loss may amount to two magnitudes. 

The position of the ecliptic in the sky is therefore of great im- 
portance, and since it is tilted at about 23 J degrees to the equator, 
it is only at certain times of the day or year that it is displayed to 
the best advantage. It will be realized that the Sun (and therefore 
the ecliptic) is at its highest in the sky at noon in midsummer, and 
at its lowest at noon in midwinter. Allowing for the daily motion 
of the sky, these times lead to the fact that the ecliptic is highest at 
midnight in winter, at sunset in the spring, at noon in summer, and 
at sunrise in the autumn. Hence these are the best times to see the 
planets. Thus, if Venus is an evening star, in the western sky after 
sunset, it will be seen to best advantage if this occurs in the spring, 
when the ecliptic is high in the sky and slopes down steeply to the 
north-west. This means that the planet is not only higher in the 
sky, but will remain for a much longer period above the horizon. 
For similar reasons, a morning star will be seen at its best on 
autumn mornings before sunrise, when the ecliptic is high in the 
east. The outer planets, which can come to opposition and are 
then in the south at midnight, are best seen when opposition 
occurs in the winter months. Clearly the summer is the least 
favourable time to observe the planets, for the ecliptic is always 
low in the sky on summer nights. 


Notes on the Planets in the monthly 

The following general notes on observing the planets are fol- 
lowed by detailed month-by-month accounts of the behaviour of 
the planets, and of other interesting phenomena. These monthly 
notes include diagrams of the planetary orbits, and of the appa- 
rent movements of the planets at favourable times of the year. 
Additional notes on other astronomical phenomena will be found 
on the following pages. 

The monthly diagrams of the orbits of the planets are intended 
to give a picture of the way in which the planets move about the 
Sun during the month. These diagrams are similar to those that 
were given many years ago in the old English Mechanic, and which 
were also adopted for some time in the Journal of the B.A.A. The 
motions of the planets are all anti-clockwise, and the movement 
during the month is indicated by the thickened line ; the longitudes 
are measured from the Equinox, marked 0°. It is difficult 
to show all the orbits to scale, since the distance of Pluto from the 
Sun is about a hundred times that of Mercury. For this reason, 
only the orbits of the inner planets (Mercury to Mars) are shown 
to scale, those of the outer planets being merely suggested in the 
diagrams. A line drawn from the Earth to any other planet will 
give a rough idea of the apparent longitude of that body, but a 
more accurate value can be obtained from the table on page 30, and 
this will enable the position of the planet to be found on the 
monthly star-charts. 

The inferior planets, Mercury and Venus, move in smaller 
orbits than that of the Earth, and so are always seen near the Sun. 
They are most obvious at the times of greatest angular distance 
from the Sun (greatest elongation), which may reach 28 degrees 
for Mercury, or 47 degrees for Venus. They are then seen as even- 
ing stars in the western sky after sunset (at eastern elongations) or 
as morning stars in the eastern sky before sunrise (at western 
elongations). The succession of phenomena, conjunctions and 
elongations, always follows the same order, but the intervals 


between them are not equal. Thus if either planet is moving round 
the far side of its orbit its motion will be to the east, in the same 
direction in which the Sun appears to be moving. It therefore 
takes much longer for the planet to overtake the Sun - that is, to 
come to superior conjunction - than it does when moving round 
to inferior conjunction, between Sun and Earth. The intervals 
given in the following table are average values ; they remain fairly 
constant in the case of Venus, which travels in an almost circular 
orbit. In the case of Mercury, however, conditions vary widely be- 
cause of the great eccentricity and inclination of the planet's orbit. 

Mercury Venus 
Inferior conj. to Elongation West 22 days 72 days 

Elongation West to Superior conj. 36 days 220 days 
Superior conj. to Elongation East 36 days 220 days 
Elongation East to Inferior conj. 22 days 72 days 

The greatest brilliancy of Venus always occurs about a month 
before greatest western elongation (as a morning star), or a month 
after greatest eastern elongation (as an evening star). No such rule 
can be given for Mercury, because its distance from Sun and Earth 
can vary over a wide range. 

Mercury is not likely to be seen unless a clear horizon is avail- 
able; it is seldom seen as much as 10 degrees above the horizon in 
the twilight sky. In general it may be said that the most favourable 
times for seeing Mercury as an evening star will be in spring, some 
days before greatest eastern elongation; in autumn it may be seen 
as a morning star some days after greatest western elongation. 

Venus is the brightest of the planets, and may be seen on occa- 
sions in broad daylight. Like Mercury, it is alternately a morning 
and an evening star, and will be highest in the sky when it is a 
morning star in autumn, or an evening star in spring. Venus is seen 
to best advantage when it comes to greatest eastern elongation in 
June ; it is then well north of the Sun in the spring months and is a 
brilliant object in the sunset sky over a long period. 

The superior planets, which travel in orbits larger than that of 
the Earth, differ from Mercury and Venus in that they can be seen 
opposite the Sun in the sky. The superior planets are morning stars 
after conjunction with the Sun, rising earlier each day until they 


come to opposition. They will then be in the south at midnight, 
and visible all night. After opposition, they are evening stars, 
setting earlier each evening until they set in the west with the Sun 
at the next conjunction. The interval between conjunctions or 
between oppositions is greatest for Mars (over two years). At the 
time of opposition, the planet is nearest the Earth, and therefore 
at its brightest. This change in brightness is most noticeable with 
Mars, whose distance from the Earth can vary considerably; the 
other superior planets are at such great distances that there is very 
little change in brightness from one opposition to another. The 
effect of altitude is, however, of importance, for at a December 
opposition the planet will be among the stars of Taurus or Gemini, 
and can then be at an altitude of more than 60 degrees in southern 
England. At a summer opposition, when the planet is in Sagit- 
tarius, it may only rise to about 15 degrees above the southern 
horizon, and so make a less impressive appearance. 

Mars, whose orbit is appreciably eccentric, comes nearest to 
the Earth at an opposition at the end of August; it may then be 
brighter even than Jupiter, but rather low in the sky in Aquarius. 
These favourable oppositions occur every fifteen or seventeen 
years (1924, 1941, 1956, 1973), but in this country the planet is 
probably better seen at an opposition in the autumn or winter, 
when it is higher in the sky. Oppositions of Mars occur at an 
average interval of 780 days, and during this time the planet makes 
a complete circuit of the sky. 

Jupiter is always a bright planet, and comes to opposition a 
month later each year, having moved, roughly speaking, from one 
zodiacal constellation to the next. 

Saturn moves much more slowly than Jupiter, and may remain 
in the same constellation for several years. The brightness of 
Saturn depends on the aspect of its rings, as well as on the distance 
from Earth and Sun. At present the rings are well open, so that the 
planet is quite a bright object. 

Uranus, Neptune and Pluto are hardly likely to attract the 
attention of observers without adequate instruments, but some 
notes on their present positions in the sky will be found in the 
February, March and May notes. 



Monthly Notes, 1964 

New Moon: January 14 Full Moon: January 28 

Earth is at perihelion on January 3 (nearest to the Sun), its 

distance from the Sun being then 91,400,000 miles. 

Mercury is at inferior conjunction on January 4, and will not be 

visible for the greater part of the month. It comes to greatest 

western elongation on January 27 (25 degrees, morning star) 

and although it is then well south of the Sun, there is just a chance 

that it may be glimpsed low in the south-east before dawn. 

Planetary Orbits in January 

Venus is an evening star, and will be a splendid object in the 
western sky at sunset until the end of May. At the beginning of 
January it will be low in the south-west, but it moves rapidly 
north during the month, so that conditions greatly improve, and 
by the end of January it sets more than three hours after the Sun. 
On January 9, Venus passes less than a degree south of Saturn, 
and the two planets may then be seen together in the twilight sky. 


A pair of binoculars will be helpful, both planets being seen in the 
same field of view. 

Mars is still theoretically an evening star, but it will not be seen 
during the month, because it is rapidly approaching conjunction, 
and it sets only a few minutes after the Sun. 


• N 


















-• r-» 





Jupiter, January-May 
Jupiter, which was at opposition in 1963 October, is an evening 
star moving direct among the stars of Pisces. It will be seen in the 
south at twilight, and it sets about midnight. Its brightness 
decreases during the month from magnitude —2- 1 to —1-9. 
Saturn is an evening star in Aquarius, but it is approaching con- 
junction and its period of visibility after sunset is rapidly decreas- 
ing. It should be possible to find the planet, during the first half 
of the month, low in the south-west for a short period after dark. 
The conjunction of Mars and Saturn on January 9 is mentioned 
in the notes on Mars above. 

A partial eclipse of the Sun takes place on January 14, but is only 
visible in Antarctica (see page 72). 

Leap Years. Our present calendar (the Gregorian calendar) is a 
modification, introduced by Pope Gregory XIII in 1582, of the 
calendar instituted by Julius Caesar. In this calendar every 


fourth year was a leap year, but in the course of fifteen centuries 
the error had accumulated so that the date of the equinox (which 
controls the date of Easter) was 10 days out. By the time the 
calendar was used in England in 1752 the error was 11 days. The 
rule for leap years in the Gregorian calendar is simple enough: 
the extra day at the end of February is added if the year is divisible 
by 4, except in the case of century years, ending in 00, which are 
only leap years if the year is divisible by 400. More simply, it is a 
leap year if the last two figures divide by 4, but if these two figures 
are zeroes, then the first two figures must divide by 4. Thus the 
year 1900 was not a leap year, but the year 2000 will be. The effect 
of this rule is that in a period of 400 years there are 97 leap years of 
366 days, and 303 common years of 365 days, making a total of 
146,097 days. The average length of the year over this period is 
therefore 365-2425 days, which is O-OO03O5 day longer than the 
tropical year (the period of revolution of the Earth from equinox 
to equinox). The error after 400 years will amount to about 3 
hours, and it will be over 3,000 years before the calendar is a whole 
day in error. 

Galileo Galilei. In 1964 we shall be celebrating the fourth cen- 
tenary of the birth of Galileo, the great Italian scientist, who was 
born on 1564 February 18. Galileo is remembered in astronomy 
mainly because of his discoveries with the telescope. He was the 
first to see the four great satellites of Jupiter, the mountains on the 
Moon, the starry structure of the Milky Way, and the phases of 
Venus, while he shares the credit for the discovery of spots on the 
Sun. Yet these discoveries, important though they were, do not 
reflect the real greatness of Galileo, for it was his method of 
dealing with scientific problems that makes his work of such out- 
standing value. His results were based on experimental evidence, 
and if he was not the first to use the experimental method, he was 
certainly a pioneer in presenting those results to the people. He 
was a public figure, and, forsaking the Latin of his predecessors, 
he stated his conclusions in the language of his day, bringing 
science out into the light for all to see. 




New Moon : February 13 Full Moon : February 27 

Mercury is now moving in to superior conjunction, and will not be 

visible during the month. 

Venus continues to be seen as a brilliant evening star, setting about 

four hours after the Sun at the end of the month. The planet is now 

well north of the Sun, and this will be noticed as it sets in the west. 

The young crescent Moon will be seen near Venus each month, 

but on each of these occasions (e.g. February 16, March 17, 

April 15) the planet will be well to the north of the Moon. Venus 

will be seen near Jupiter on the nights of February 27 and 28. 

Planetary Orbits in February 

Mars is at superior conjunction on February 17, and will not be 
visible during the month. It will be seen from the diagram of the 
planetary orbits that at the time of conjunction Mars is near 
perihelion, at a distance of 129 million miles from the Sun. 

Jupiter is a bright evening star in Pisces, and will be seen to the 


left of the Great Square of Pegasus as that star-group sets in the 
west. Jupiter will be near Venus at the end of the month, but 
the two planets are easily distinguished, Venus being much the 
brighter (Venus, magnitude —3-6, Jupiter —1-7). 

Saturn, now on the far side of its orbit (see diagram above), is at 
conjunction on February 15, and will not be visible during the 

Uranus is at opposition on February 27, when it may be found in 
the constellation Leo (see diagram, page 64). The magnitude of the 
planet at this time is +5-7, and it should just be possible to see it 
with the naked eye; in a small telescope it appears as a greenish 
disk. The distance of Uranus at opposition is about 1,610 million 
miles from the Earth. 

The Sundial. At this time of year - and again in November - a 
sundial will be found to be about a quarter of an hour in error as 
compared with a clock. The difference is a demonstration of the 
fact that the true Sun is not a good timekeeper; it does not travel 
uniformly round the sky, whereas our clocks keep mean time, 
that is, they maintain a uniform average rate which, over the 
years, matches the motion of the true Sun. The difference between 
apparent time (as told by the Sun), and the mean time of our 
clocks is called the equation of time. It may be either positive or 
negative, that is, the sundial may be either slow or fast as com- 
pared with a clock keeping mean time. A sundial will be found to 
be about 14 minutes slow in February, while in late October and 
early November it will be as much as 16 minutes fast. The equa- 
tion of time is zero on four occasions during the year - about 
April 15, June 13, September 1 and December 25, and only on 
these four days is the Sun due south at noon. 

The variations in the rate at which the Sun appears to travel 
are due to two effects. First, the Sun does not travel round 
the equator (along which we measure longitude and intervals of 
time), but round the ecliptic; and secondly, the Earth's orbit is 
not circular but is an ellipse, and the Sun is nearest to us (and 


therefore travelling most rapidly) at the beginning of January. 
Each effect causes a displacement of the Sun's position, and this 
displacement goes through a complete cycle of changes in the 
course of the year. The sum of the two effects is the equation of 
time, which vanishes on the four dates already mentioned, and 
has four maximum values: -14 m about February 12, +4 m on 
May 14, -6 m on July 27 and +16 m on November 3. The cycle 
then starts again, and it will be noticed that the interval between 
the two largest maxima, on November 3 and February 12, is only 
three months; during this period the equation of time is changing 
most rapidly, and about December 23 it is altering by as much as 
half a minute a day. The effect of this on the times of sunrise and 
sunset is mentioned in the note on page 71 . 

Whatever the design of a sundial, the essential part of the 
instrument is the straight edge or gnomon which casts the shadow. 
This gnomon is erected so as to be parallel to the Earth's axis, 
that is, the angle of the gnomon must equal the latitude of the 
place. It follows that an accurate sundial must be designed to suit 
its situation - one cannot buy a sundial at a super-market! The 
dial on which the shadow of the gnomon is cast is usually hori- 
zontal, but may be vertical or inclined, or even part of a circular 
arc. The assumption is made that the Sun is due south at noon, so 
that the 12-hour mark is measured due north, and the other hours 
are marked off east and west at the rate of 15 degrees for each 
hour. It can scarcely be said that the sundial is a useful instrument, 
but there is a certain romantic charm about an old sundial, and 
many of them are provided with mottoes, witty, wise, or merely 
humorous. The late Hilaire Belloc provided a number of suitable 
mottoes for sundials, but perhaps the most pointed of these is 
the simple rhyme 

/ am a sundial, and I make a botch 
Of what is done far better by a watch. 





New Moon : March 1 4 Full Moon : March 28 
Equinox: March 20 

Mercury is at superior conjunction on March 13, and for the 
greater part of the month will remain invisible. Towards the end 
of March, however, it moves out again from the Sun to become 
an evening star, and there is a chance of seeing this elusive 
planet in western sky after sunset. (See notes and diagram on 
page 45). On March 31, Mercury is 3 degrees north (i.e. above and 
to the right) of Jupiter, but there is little risk of confusion, as 
Jupiter is so much the brighter of the two. 

Planetary Orbits in March 

Venus now grows noticeably brighter as an evening star, and sets 
more than 4 hours after the Sun. At the equinox, when the Sun is 
on the equator, Venus is 18 degrees north and 45 degrees east of 
the Sun. 

Mars has now passed conjunction, and is theoretically a morning 


star. It moves out from the Sun very slowly, and by the end of 

March it is still only 9 degrees west of the Sun, so that it will not 

be seen during the month. 

Jupiter is still an evening star, but its period of visibility after 

sunset grows shorter, and by the end of the month it sets a little 

north of west about 1 \ hours after the Sun. 

Saturn now becomes a morning star, but is not likely to be seen 

until the end of March, when it rises to the south of east about an 

hour before the Sun. 

Pluto is at opposition on March 3; it is in Leo, appearing as a 

faint star of the fifteenth magnitude. 

Equinoxes and Solstices. It will be noticed that the equinox occurs 

this year on March 20, and this may seem to many readers to be 

rather earlier than usual. The date of an equinox is not rigidly 

fixed - it is defined as the time at which the Sun reaches the First 

Point of Aries, i.e. when its longitude is degrees. Since the actual 

period of revolution of the Earth with respect to the equinox is 

365-2422 days, the date of the equinox moves forward each year 

by the odd 0-2422 day (about 6 hours), and drops back a day in 

leap years. This applies equally to the other equinox and to both 

solstices, all of which show the same behaviour — advancing by 

about 6 hours in common years, and falling back by about 18 

hours in leap years. 











d h 

1958 Mar. 21 





June 21 

22 Dec. 

22 09 

1959 21 






22 15 

1960 20 






21 20 

1961 20 






22 02 

1962 21 






22 08 

1963 21 






22 14 

1964 20 






21 20 

1965 20 






22 02 

It will be seen that the earliest dates are always in 

leap years, 

and that the dates i 

repeat themselves 


closely every 

4 years, 


although there remains a small error which accumulates. As a 
result, the dates move slowly backwards throughout the 400-year 
cycle of the Gregorian calendar. By the year 2000 the date of the 
equinox will be March 20 d 07 h , but the year 2000 is a leap year, 
and the dates will continue to move back, until 2096, when the 
equinox will be on March 19 d 14 h . 

The birthplace of stars. The stars of Orion are of a hotter and 
whiter type than our Sun, but there are two notable exceptions. 
Betelgeuse, 'the shoulder of the giant', is slightly red in colour and 
its light varies in an irregular manner. It is red because it is at a 
lower temperature than the Sun, yet it gives out 10,000 times as 
much light. This is a giant star, at least 300 times as big as the 
Sun, and if our Sun were as big as this it would extend beyond the 
orbit of Mars. The star Rigel, on the other hand, although not so 
huge, is at least 20,000 times as luminous as our Sun. Now, if a 
star of this size is pouring out light and heat at this astonishing 
rate, it obviously cannot last very long. The Sun, which is believed 
to be at least 3,000 million years old, is still going strong, and 
promises to do so for many millions of years. But Rigel could not 
possibly maintain its present output of energy for more than a 
few million years. The conclusion is obvious - that Rigel is much 
younger than the Sun, and therefore that stars must have been 
formed at different times in the past - perhaps they are still being 

There is an increasing amount of evidence that this is indeed 
the case, and that stars are born in the vast clouds of dust and gas 
that occur in the spiral arms of our Galaxy, in regions such as the 
great nebula in Orion. Some years ago a photograph showed 
five small areas of glowing nebula in one part of this area. A 
more recent photograph of the same region showed seven glowing 
spots, so that something must be happening here, and it is tempt- 
ing to conclude that we are witnessing the formation of two new 
stars. At any rate, there is no doubt that the evolution of stars is 
a continuous process, not only in our own Galaxy, but in thou- 
sands of millions of other galaxies throughout the universe. 




New Moon: April 12 Full Moon: April 26 
Mercury is at greatest eastern elongation on April 7 (19 degrees; 
evening star), and will be favourably placed for observation at the 
beginning of the month in the western sky just after sunset. The 
diagram shows the changes in altitude and azimuth (true bearing 
from the north through east, south and west) of Mercury on 
successive evenings at a time when the Sun is 6 degrees below the 
horizon; this will be about 35 minutes after sunset at this season. 


5 5° 

Apr 5 


Apr 15 

Apr 20 * 






Mercury, April 

The sizes of the circles give an approximate indication of the 
expected brightness of the planet; it will be noticed that Mercury 
is much brighter before the date of greatest elongation. There is a 
possibility of confusion with the planet Jupiter, which is in the 
same part of the sky, but is very much brighter than Mercury, and 
several degrees nearer to the horizon. 

Venus is also at greatest eastern elongation this month (46 degrees 
from the Sun on April 10), and is in high northern declination, so 
that it presents a splendid appearance for several hours after 
sunset. At the end of the month it will be almost midnight before 
Venus sets, at a point well north of west. At the beginning of the 



month the planet passes just south of the Pleiades, and on April 14 
will be seen some degrees north of Aldebaran. 

Planetary Orbits in April 

Mars is a morning star, but rises only a few minutes before the 
Sun at the end of April. 

Jupiter is in conjunction with the Sun on April 22, but it may be 
possible to see the planet for a short while in the first few days of 
the month, in the west in the evening twilight. 

Saturn now begins to appear as a morning star, rising in the 
south-east among the stars of Aquarius. 

The motion of the planets. In general, the planets move to the left 
across our sky, but this motion is not a continuous one, like that 
of the Sun and Moon. These two bodies always move eastwards 
in this way (this is direct motion), but the planets behave differ- 
ently, for at certain definite intervals they pause and go backwards 
for some distance (this is retrograde motion), making a loop in the 


sky. The effect is very much the same as watching a race from the 
grandstand; the runners pass in front of you, moving to the right, 
but as they round the bend, they are moving away from you, and 
on the other side of the track they are moving to the left. If the 
Earth stood still in space, this is all that would happen. We should 
see Venus, for instance, going round the Sun, just shuttling to and 
fro, moving to the right in front of the Sun and to the left behind 
it. But because the Earth is moving, the Sun appears to travel 
eastwards round the sky, taking Venus with it. Thus the path of 
the planet is drawn out into a long line with loops in it, each loop 
representing one revolution of the planet about the Sun. 

Now, it is not difficult to realize that if you were standing on the 
surface of Venus you would see the Earth doing exactly the same 
things. Each planet sees the other making the same direct and 
retrograde motions at the same time, but in diametrically opposite 
parts of the sky. So the behaviour of Mars, Jupiter or Saturn, as 
we see them from the Earth, is just a copy of the movements of the 
Earth as they would see them. When planet and Earth are on the 
same side of the Sun, the apparent motion is retrograde, and the 
opposition of an outer planet, or the inferior conjunction of an 
inner planet will occur in the middle of this retrograde movement. 
When Earth and planet are on opposite sides of the Sun, the 
motion is direct, and this direct movement takes up much more 
time than the retrograde one because of the Earth's movement in 
the same direction as the planet. It can be seen that the nearer the 
planet comes to the Earth, the larger is the loop in its path, and the 
faster is its apparent motion. The large loop and the long period of 
rapid direct motion of Mars are quite characteristic of this planet. 
The retrograde motion of Mercury and Venus is seldom noticed, 
because it occurs at the time of inferior conjunction, when these 
planets are drawing close to the Sun and cannot be observed 
against the background of stars. 




New Moon: May 11 Full Moon: May 26 

Mercury was at inferior conjunction at the end of April, and comes 
to greatest western elongation on May 24 (25 degrees; morning 
star). At this time, however, it is well south of the Sun, and is 
unlikely to be seen in the bright dawn sky. 

Venus reaches its greatest brilliancy as an evening star on May 13 
(magnitude —4-2). It is now swinging round towards inferior con- 
junction, and its apparent motion eastwards becomes slower; at 
the end of May it reaches a stationary point, and then begins to 
move westwards, and its elongation from the Sun rapidly decreases. 
As a result, the time of setting becomes earlier each night, and at 
the end of May, Venus sets only 2 hours after the Sun. In a small 
telescope the planet shows the crescent phase of a young moon, the 
horns of the crescent pointing east, i.e. to the left. 

Mars is a morning star, but is still too close to the Sun to be readily 
visible. There is a conjunction with Jupiter on May 19, when the 

Planetary Orbits in May 


two planets will be less than a degree apart. Mercury is also in the 
same part of the sky, but unfortunately these planets all rise only a 
few minutes before the Sun, and this interesting configuration is 
not likely to be seen in northern latitudes. 

Jupiter now begins to appear as a morning star, but is unlikely to 
be seen until the end of the month. 

Saturn is a morning star, rising in the south-east about 2 hours 
before sunrise at the beginning of May. It will be seen among the 
stars of Aquarius, to the right of the Great Square of Pegasus. The 
planet is brighter than any other star in the neighbourhood (mag- 
nitude + 1-1) and this will make it easy to recognize. 








>^ Pleiades 

• • 







Aldebaran V Hyades ^**«s^l--. 



/ ** - 

^- Conjunction 
^J May 19 

r*"*-"i *-- May J 

4 """-^ 



^-. • > • 



/ * 

• • 

•— — / 






Jupiter and Mars 

Neptune is at opposition on May 7, and may be found about 2 
degrees east and a degree north of the third magnitude star Alpha 
Librae (Zuben el Genubi). Neptune is not visible to the naked eye, 
but with a small telescope it may be seen as a greenish disk of 
magnitude +7-7. At opposition, the distance of Neptune from the 
Earth is about 2,720 million miles. 


Cassiopeia. On a May night the constellation Cassiopeia will be 
seen low down near the northern horizon, its very obvious shape 
(like the letter W) and its bright stars, making it a conspicuous 
object in this part of the sky. Its position may also help the observer 
to find the Plough (reversing the usual procedure) for the Plough is 
on the opposite side of the Pole Star, and at this time is almost 
directly overhead in a most unfamiliar position. Cassiopeia is full 
of interesting objects, for the greater part of it is immersed in the 
Milky Way. It was in this constellation that Tycho Brahe observed 
the brilliant supernova of 1572 - one of the three supernovae which 
have been recorded in our Galaxy. The new star, which was as 
bright as the planet Venus, and was even visible in daylight, was 
the subject of much speculation. The scientists of the day adhered 
to the teachings of Aristotle, who had maintained that in the starry 
sphere everything was eternal and unchanging. This could not be a 
comet, for it did not move among the stars. Was it then some con- 
densation of fiery vapours in the upper air? To these questions 
Tycho, then a young man of 26, gave a scientific answer. He 
repeatedly measured the position of the star, with reference to the 
other stars of Cassiopeia and to the Pole Star, and showed that the 
nova did not change its position in the slightest, whether Cassiopeia 
was in the zenith or low down on the northern horizon. If the star 
had been as near as the Moon it would have shown a parallax of at 
least a degree, that is, it would have appeared one degree lower 
(with respect to the neighbouring stars) in the sky when it was low 
in the north. So the star must have been at a distance greater than 
the Moon, and, in spite of Aristotle, there were changes taking 
place in the Universe. The new star finally disappeared from view 
in 1574, and today there is no visible object in its place. Radio 
astronomers, however, have detected a faint radio source in this 
position. It is interesting to note that in another part of Cassiopeia 
ties the most powerful of all radio sources, called Cassiopeia A, 
and this, too, appears to be the remnants of a supernova, although 
it is at a much greater distance, and its appearance was not 




New Moon: June 10 Full Moon: June 25 
Solstice: June 21 

Mercury is moving towards superior conjunction on June 27, and 
will not be visible during the month. 

Venus is at inferior conjunction on June 19, and rapidly disappears 
from view as an evening star. It reappears just as rapidly in the 
dawn sky as a morning star at the end of June. At the conjunction 
on June 19, Venus is only 27 million miles from the Earth. 

Planetary Orbits in June 

Mars is a morning star, but emerges only slowly from the Sun's 
rays ; it rises about an hour before sunrise at the beginning of June, 
and about 2 hours before the Sun at the end of the month. Its 
magnitude is + 1 -6, and it moves from Aries into Taurus, being 
seen between the Pleiades and the Hyades about June 20. 

Jupiter is a morning star and may be seen in the east before dawn. 
The planet is in the constellation Aries and is moving eastwards 


towards the star-clusters Hyades and Pleiades. At the end of June, 
Jupiter rises about 3 hours before the Sun; its magnitude is then 


Saturn is a morning star, rising about midnight in the south-east. 
The planet reaches a stationary point on June 16 and then begins 
its retrograde movement (see diagram on page 58). Magnitude 
+ 1-0. 

A partial eclipse of the Sun on June 10 will be visible only in 


A total eclipse of the Moon on June 24-25 will be visible in the 

British Isles. It begins about an hour before midnight (see details 

on page 72) and becomes total about a quarter of an hour after 

midnight. Total eclipse lasts until l h 57 m on June 25, and the eclipse 

endsat3 h 03 m . 

Parallax. No two people ever see the Moon in exactly the same 
place in the sky, the change in position from one observer to the 
other causing a change in the apparent position of the Moon, 
which is near enough to the Earth to show a large parallax. The 
positions of the Moon which are given in the tables are calculated 
for an observer at the centre of the Earth, but at any other point on 
the Earth's surface, the apparent position of the Moon will be 
different. The maximum value of the parallax is nearly a degree 
when the Moon is on the horizon, but the parallax of more distant 
objects is much less ; it amounts to a few seconds of arc for the Sun 
and the planets, and is quite unmeasurable for the stars. We there- 
fore measure the parallax of the stars in a different way, using the 
radius of the Earth's orbit as a base-line. For members of the solar 
system, however, the parallax is quite measureable when the 
equatorial radius of the Earth is taken as the base-line. The angle 
subtended at the distant body by the Earth's equatorial radius is 
then called the equatorial horizontal parallax (because it is the 
maximum value of the parallax, observed when the body is on the 
observer's horizon). The horizontal parallax of the Sun (called the 
solar parallax) is 8"-79, and the parallaxes of the planets are found 
simply by dividing this figure by the distance of the planet; the 


values may therefore range from about 30" for Venus when at its 
nearest to us, to the quarter of a second for Pluto. By contrast the 
parallax of the Moon is quite large, and it cannot be calculated in 
any such simple manner. The average value is 57', and since the 
effect of parallax is always to displace the body vertically down- 
wards towards the horizon, this is the average amount of the 
depression of the Moon when it is on the horizon. As a result, this 
amount has to be included in calculations of the times of moonrise 
and moonset. Similarly this large correction must be included in 
calculations of eclipses or occultations, which can become very 
troublesome in border-line cases, as when the observer is near the 
edge of the shadow in a solar eclipse (i.e. near the edge of the 
eclipse track across the Earth) or is observing an occultation in 
which the star just grazes the limb of the Moon. 

In the case of a satellite which is nearer to us than the Moon, 
the parallax can be very large indeed. Some of the natural satellites 
show this very well, perhaps the best example being Phobos, the 
inner satellite of Mars. This little body revolves about the planet at 
a distance of 5,800 miles, so that it is only about 3,700 miles from 
the surface of Mars. Its parallax is as much as 21 degrees, and this 
means that Phobos is invisible from any place at latitudes greater 
than 69 degrees. Some of the artificial satellites of the Earth are 
even closer than this, and a satellite at a height of 1 ,000 miles above 
the Earth's surface will have a parallax of about 53 degrees. If it 
travelled in an equatorial orbit, it would only be visible in a broad 
belt stretching 37 degrees north and south of the equator. It is for 
this reason that the satellites are usually launched in an inclined 
orbit, so that they may be visible over the greater part of the Earth. 




New Moon: July 9 Full Moon: July 24 

Earth is at aphelion (farthest from the Sun) on July 5, its distance 
from the Sun being then about 94,500,000 miles. 
Mercury was at superior conjunction at the end of June, and will 
be too close to the Sun to be seen during the month of July. 
Venus moves rapidly out from the Sun to become a brilliant object 
in the morning sky. It is again at greatest brilliancy on July 26 
(magnitude —4-2), and at this time it may be seen in a small tele- 
scope as a small crescent moon, with the horns of the crescent 
pointing to the west. On the morning of July 18, Venus will be 
found to be about 5 degrees south of Mars, but it is more than 100 
times as bright as that planet (Venus, magnitude —4-1, Mars 
+ 1-7). 

Planetary Orbits in July 

Mars is a morning star moving direct in Taurus. On July 1 it passes 
about 6 degrees north of Aldebaran (magnitudes: Mars +1-6, 


Aldebaran +1-1), and on July 18 it will be 5 degrees north of 
Venus. On this occasion, the apparent motion of Mars is actually 
greater than that of Venus, but this state of affairs does not last 
very long, and Venus will soon catch up with Mars, and pass that 
planet in August. At the end of July, Mars rises about 3 hours 
before sunrise. 

Jupiter is a bright morning star (magnitude — 1 -7 to — 1 -9) moving 
direct in Aries. At the end of the month the planet rises at mid- 
night and passes into the constellation Taurus. 

Saturn now rises well before midnight, and will be seen in the 
south-east among the stars of Aquarius. It is growing appreciably 
brighter as it approaches opposition. 

A partial eclipse of the Sun on July 9 is visible only in Arctic 

Lyra. The bright star Vega is easy to find on a July night, for at 
midnight it is almost directly overhead. This is the brightest star of 
the constellation Lyra, which is supposed to represent the lyre 
which Orpheus played, and in which are to be found a variety of 
interesting objects. Just to the east of Vega is the star Epsilon 
Lyrae, which those with keen sight may recognize as a double star. 
In a telescope each of the two stars is seen to be double, the four 
almost identical stars forming a quadruple system (see page 209). 
To the south of this star and Vega lie four stars arranged in a small 
parallelogram, and this is all that the eye usually sees of this con- 
stellation. The two most southerly stars are Gamma (to the east) 
and (to the west) Beta Lyrae, and half-way between them lies the 
famous Ring Nebula (page 210). In an ordinary telescope this 
appears as an almost perfect luminous ring, a nebula, shining with 
the light of glowing gases. In a powerful instrument the dark 
interior of the ring is seen to be glowing faintly, and in the centre is 
a small star. The star is difficult to see, but easy to photograph - it 
it an intensely hot star, and its ultra-violet radiation makes the 
ring of gases glow with light. It is not really a ring, but a hollow 
shell, formed probably in the past by some great explosion, when 


the star threw off part of its surface as a gas cloud. The Ring 
Nebula is typical of the so-called planetary nebulae, which are 
badly named, although they may look a little like a planet out of 
focus. Nearly four hundred of these objects are known, most of 
them in or near the Milky Way. 

Another interesting object in Lyra is the star Beta Lyrae, a very 
remarkable variable star. The variations in its light were first 
reported in 1785 by John Goodricke, the remarkable deaf and 
dumb astronomer of York. He showed that the light of the star 
varied in a regular manner every 13 days, and although he did not 
attempt to give an explanation, it soon became clear that this was a 
case of an eclipsing binary star. There is actually a double variation 
of light, which sinks to 58 per cent of its value at the primary 
eclipse when the fainter star is in front, and to 91 per cent when 
the brighter star hides the other. The number of observations of 
this star must be a record, yet it still remains something of a 
mystery. Its spectrum is so complicated - there is no other bright 
star with a spectrum quite like it - that all of its problems have not 
yet been solved. We do know, however, that the system consists of 
two huge stars so close together that their tidal forces have drawn 
them out into an elliptical shape, and that they are almost touch- 
ing. The brighter star, which we know most about, is perhaps 60 
million miles across, and it is revolving in an orbit only 20 million 
miles in radius, so that the centre of the orbit must He inside the 
star. The two stars are surrounded by a shell of luminous gas which 
is continuously expanding outwards, and the stars are revolving 
inside this gaseous mantle. As they do so, they shed part of their 
surfaces, the bright star giving off a dense stream of hot gases 
which flows round the other star, and this, in its turn, emits a 
stream of cooler gas. We rather lose track of the gases at this point, 
but they must contribute to the content of the great expanding 
envelope which surrounds the whole system. This is obviously a 
very exceptional system, but it is the exception that proves the rule, 
and provides a great deal of the interest in modern astronomy. 




New Moon: August 7 Full Moon: August 23 

Mercury is at greatest eastern elongation (27 degrees; morning 

star) on August 5, but it is then well south of the Sun, and will not 

reach a sufficient altitude to be seen in the dawn sky. 

Venus is now at its best as a morning star, rising nearly 4 hours 

before the Sun, and reaching greatest western elongation (46 

degrees) on August 29. The planet will again be seen near Mars at 

the end of the month (4 degrees south of Mars on August 28). 

Planetary Orbits in August 

Mars is a morning star in Gemini, and now rises well before the 
Sun. It is not very bright as yet (magnitude + 1 -7), but by the end 
of August it will form a striking configuration with the Twins, 
Castor and Pollux, and on August 28 Venus will pass about 4 
degrees south of Mars. This will be the third successive conjunc- 
tion of Mars and Venus within a year, the two previous occasions 
being on 1963 November 20 and 1964 July 18. 



Jupiter now rises well before midnight, and will be seen on the 
borders of Aries and Taurus, to the west of the Pleiades. The planet 
is now somewhat brighter, reaching magnitude —2-1 at the end of 
August. The autumn months afford a suitable opportunity for 
watching the various phenomena of Jupiter's satellites; during the 
present apparition only the three inner satellites undergo the usual 
series of eclipses, transits and occultations. 






Saturn is at opposition on August 24, and is then visible all night. 
It should easily be recognized as the brightest object in the constel- 
lation Aquarius, its magnitude being +0-6. The distance at opposi- 
tion is 816 million miles, and although this is less than at the 1963 
opposition, the planet is not quite as bright because the rings are 
now closing; at opposition they are tilted to our line of sight at 
about 9 degrees. At a more favourable opposition, when the rings 
are fully open, the planet may be a whole magnitude brighter. The 
rings of Saturn, as well as its largest satellite Titan, may be seen in 
quite a small telescope (see note on page 64). 

Meteor streams. It is just a century since it was shown that there 


was a definite connexion between certain comets and some of the 
annual showers of shooting stars. One of the first orbits to be 
investigated in this way was that of the August meteors, the Per- 
seids, which were found to travel round the Sun in the same path as 
Turtle's comet of 1862. The assumption is made that meteors are 
caused by the debris of comets - the dust that they leave behind 
them as they travel round the Sun - but this trail of dust must 
come very close to the Earth's orbit, so that only a few comets can 
give rise to meteor showers in this way. The Perseids are always to 
be seen in a clear night in the first two weeks of August, rushing 
swiftly across any part of the sky, but always along straight 
lines which appear to radiate from a point high up in Perseus, on 
the border with Cassiopeia. The Perseids were once known as the 
'Tears of St. Lawrence', because they were seen at their best on 
August 10, the Feast of St. Lawrence. But like all such paths in 
space, the orbit of the Perseids twists slowly round, so that the 
place where it cuts the Earth's orbit has moved forward, and the 
Earth reaches this point on August 12. If the dust were concen- 
trated in one spot, there would be just one display of shooting stars 
on that night, but the Perseid stream is an ancient one - it has been 
recorded in the archives as far back as the year a.d. 830 -and so the 
dust has spread out into a broad belt round the orbit. As a result, 
Perseid meteors may be seen at any time between July 27 and August 
17, although they still reach a maximum number on August 12. 
The orbit of the Perseids is a large one, and the dust takes 33 
years to go round the Sun. As a contrast, the orbit of the December 
Geminids is an eccentric ellipse, in which the dust takes only about 
20 months to complete a revolution about the Sun. The Geminids 
rank with the Perseids in producing a good shower of meteors, and 
on the night of maximum, December 12, an observer may expect 
to see about one Geminid per minute, this figure referring to the 
whole sky, which, however, cannot all be watched at the same time. 
The Geminid meteors appear to radiate from a point in Gemini, 
near the star Castor; they have no long history, like the Perseids or 
Leonids, and are probably of more recent formation, although no 
known comet has an orbit so small. 




New Moon: September 6 Full Moon: September 21 
Equinox: September 23 

Mercury is at inferior conjunction on September 2, but it moves 
rapidly to greatest western elongation (18 degrees; morning star) 
on September 18, when it will be well placed for observation. The 
diagram shows the changes in altitude and azimuth of Mercury on 
successive mornings when the Sun is 6 degrees below the horizon; 
this is about 30 minutes before sunrise at this time of year. The 
changes in brightness are roughly indicated by the sizes of the 
circles; it will be seen that Mercury is brightest after the date of 
western elongation. 

Sep 17 ~.Sep 22 


Sep 12 

Sep 27 

Oct 2 






Mercury, September 

Venus is a morning star, and although a little less bright (mag- 
nitude — 3-9 to —3-7) it is still a fine object in the eastern sky at 
dawn. The planet remains well north of the Sun, and at the 
equinox, with the Sun on the equator, Venus still has a declination 
of 15 degrees north. 

Mars is also a morning star in Gemini, and at the beginning of the 
month is only a few degrees to the north-west of Venus. Its direct 
motion takes it some degrees south of Pollux on September 5 
(magnitudes Mars +1-6, Castor + 1 - 6, Pollux + 1 -2) and it moves 



into Cancer in the middle of May. It will be south of the star 
cluster Praesepe at the end of the month. 

Planetary Orbits in September 

Jupiter is a brilliant evening star (magnitude -2-2), rising in the 
late evening in Taurus. It is now moving slowly eastwards to the 
south and west of the Pleiades, but it does not reach this cluster, as 
it comes to a stationary point on September 14, and then begins its 
retrograde motion. Jupiter will be seen just north of the Moon (4 
days past the Full) on the night of September 25. 
Saturn is an evening star, and will be seen in the south in the late 
evening. It is still moving retrograde in Aquarius. 
Vesta may reach magnitude 6 at the time of opposition on Sep- 
tember 2. (See note on page 76). 

The four great moons of Jupiter. The four largest satellites of 
Jupiter are always a fascinating study, and may be seen with quite 
a small telescope, appearing as four bright pin-points of light that 
move round the belted planet. Their orbits are almost edge-on to 


us, so that they pass in front of Jupiter as they move from east to 
west, swing out into space, pause, and swing back again. This time 
they pass behind the planet, and may either be occulted by the 
planet or undergo eclipse in Jupiter's enormous shadow. The tran- 
sit of a satellite across the face of Jupiter is always preceded or 
followed by a transit of the satellite's shadow, but these are not 
easy to see in a small instrument, since both satellite and shadow 
tend to merge into the background formed by the bright surface of 
Jupiter. Eclipses, however, are easily seen, and are always interest- 

Jupiter has twelve moons, but the other eight are much too small 
and faint to be seen with ordinary telescopes. Even from the surface 
of Jupiter, the outer seven would be invisible without quite a large 
telescope. The four big satellites, which are about the same size as 
our own Moon, would not appear as bright as our Moon does to 
us, because the Sun is five times as far away. Its light would there- 
fore be only about 4 per cent of the amount that we receive on 
Earth. Satellite I, which is about the same distance from Jupiter as 
the Moon is from the Earth, would appear to be about the same 
size as our Moon, but a good deal less bright ; the other three would 
appear progressively smaller and fainter. All four moons would 
exhibit the usual phases, but satellites I, II and III would be seen in 
eclipse at every revolution. Only satellite IV is far enough away 
from Jupiter to escape the great shadow of the planet, on those 
occasions when it is tilted to its greatest extent towards or away 
from the Sun. This tilt is only about 3 degrees, but this is enough to 
allow satellite IV to pass above or below the shadow. Jupiter is 
tilted in this way at the present time and satellite IV does not 
undergo any of these phenomena. The fifth satellite, nearest to 
Jupiter, is very much smaller, but it is of interest because it travels 
round Jupiter at a distance of 112,500 miles (half the distance of 
the Moon from the Earth) in a period of 12 hours. This means that 
it is the fastest natural satellite in the solar system, moving at 1,000 
miles a minute, or twenty-five times as fast as our Moon. 



New Moon: October 5 Full Moon: October 21 

Mercury is at superior conjunction on October 15 and will not be 

visible during the month. 

Venus still rises some hours before the Sun, and is a brilliant object 

in the east before dawn. Two interesting conjunctions of Venus 

take place during this month, and should be observable with 

binoculars. On October 5 the planet passes less than half a degree 

south of Regulus, and on October 17 it will be very close to the 

Planetary Orbits in October 

planet Uranus. The closest approach occurs at about midnight, but 
even at 4 11 Venus will be less than a quarter of a degree north of 
Uranus, and with any sort of optical aid both planets should be 
visible in the same field of view. 

Mars is a morning star, rising just after midnight. It moves from 
Cancer into Leo at the middle of October, and begins to brighten a 
little (magnitude + 1 -5 to +1 -4) as its distance decreases. At the 



' LEO .^^\< 



Praesepe „ _ 



_ » <- — 


• -* 

HYDRA ./ ^| 

Marc a«rf Uranus 

end of the month Mars will be found near Regulus (magnitude +1 -3) . 

Jupiter now rises north of east in mid-evening. It is moving retro- 
grade on the borders of Taurus and Aries, and its brightness con- 
tinues to increase as it approaches opposition (magnitude —2-4). 
The planet will again be seen close to the Moon on the night of 
October 22. 

Saturn is an evening star in the south in the early evening hours, 
and is visible for most of the night. It is now moving slowly among 
the stars of Aquarius, and is a little less bright (magnitude +0-8). 

Saturn's satellite Titan. Although fainter than the four big satellites 
of Jupiter, Saturn's satellite Titan is quite a suitable object for a 
small telescope. Titan is the largest satellite in the solar system, and 
it appears to be fainter than those of Jupiter merely because it is 
about twice as far from us and from the Sun. It revolves about 
Saturn in a period of about 16 days, but under normal conditions 
it does not undergo the succession of transits and eclipses that 
make the four moons of Jupiter so fascinating to watch. Saturn is 
tilted at such an angle (28 degrees) that Titan appears to pass above 
or below the disk of the planet at each conjunction ; it is only when 
the planet is seen at such an angle that the rings and the orbits of 


the satellites appear almost edge-on that these phenomena can take 
place. This does not happen in 1964, but the rings are closing, and 
the eclipses and transits of Titan will be seen again in two or three 
years' time. Diagrams showing the position of Titan are given 
annually in the Handbook of the British Astronomical Association. 

Aquarius. The constellation Aquarius, in which Saturn is to be seen 
at the present time, is one of the many star groups in this part of 
the sky that have something to do with water. There is the dolphin 
(Delphinus) and the fishes (Pisces and Piscis Austrinus), the whale 
(Cetus) and the sea-serpent (Hydra) ; and even the goat (Capricor- 
nus) is a sea-goat, half animal, half fish. There, too, is the River 
Eridanus, winding down to the southern skies, whose waters have 
their magical source in the jar which Aquarius is holding. The 
constellation is an old one, and the water which flows from the jar 
was once the source of a proverb, as well as of a river. Manilius, 
the Latin poet, in his astronomical poem, ends his description of 
Aquarius with the words '. . . and so the urn flows on', and this 
became a common figure of speech in referring to people who will 
keep on talking. In some old English books Aquarius is referred to 
as 'The Skinker', and this old Anglo-Saxon word may still be 
found in some modern dictionaries. It means a tapster, one who 
serves drink, and it comes as something of a shock to have such a 
word applied to a star group. 

The International Astronomical Union. The International Astro- 
nomical Union, which co-ordinates the work of astronomers all 
over the world, is holding its twelfth General Assembly in Ham- 
burg this year. These conferences are held every three years, and 
the last meeting in Berkeley, California, in 1961, brought together 
nearly 800 astronomers from thirty-eight different countries. Their 
discussions covered every branch of astronomy, both practical and 
theoretical, from the history of astronomy to the most modern 
theories and equipment, from meteors to magneto-hydrodynamics, 
from the solar system to the most distant galaxies. Hamburg has 
much to offer the assembled scientists, and the ample facilities of 
the University should ensure the success of this meeting. 




New Moon: November 4 Full Moon: November 19 

Mercury is at greatest eastern elongation on November 30 (21 
degrees; evening star), but is then well south of the Sun, and will 
not reach a sufficient altitude to be visible in the twilight sky. 

Venus is still a fine object in the east at dawn (magnitude —3-5). 
The planet crosses the equator into southern declinations on 
November 3, but it is still well north of the Sun. 

Planetary Orbits in November 

Mars rises at midnight at the beginning of the month, and is in the 

south at dawn. It is now moving more slowly through Leo, and 

passes rather more than a degree north of Regulus on November 4 

(magnitudes Mars +1-4, Regulus +1-3). Mars is now growing 

noticeably brighter, and reaches magnitude +1-0 at the end of 


Jupiter is now at its brightest as an evening star (magnitude —2-4), 


and reaches opposition on November 13. The planet moves west- 
wards into Aries at the beginning of the month, and will remain in 
this constellation for the rest of the year. This opposition is a very 
favourable one, Jupiter being now 17 degrees north of the equator 
and high in the sky at midnight. The distance at opposition is 
almost exactly four astronomical units, or 372 million miles. 

Saturn is at a stationary point on November 2, and then begins its 
direct motion eastwards once more. It sets at midnight at the 
beginning of the month in the south-west. 

The Leonids. In November, particularly about the 16th of the 
month, it is possible to see a few fast-moving shooting stars, which 
appear to come from a point above the Sickle of Leo. These are 
called the Leonids, and although the display is likely to be rather 
disappointing, this shower is of considerable interest. The Leonids 
are among the fastest moving of all meteors, because in November 
the Earth is moving towards the star Regulus, and since the 
Leonids are coming from that direction, they meet the Earth 
almost head-on. Travelling through our atmosphere at more than 
40 miles a second, they burn themselves out to form swift straight 
streaks of light which may be seen in any part of the sky, but which 
all appear to radiate, like the spokes of a wheel, from this point in 
Leo. This is an effect of perspective, just as railway lines appear to 
vanish together at a point in the distance. Knowing the position of 
the Earth at the time, and the point in the sky from which the 
meteors have come, it is possible to calculate the orbit in which the 
meteoric dust is travelling. In the case of the Leonids, the orbit is 
the same as that of Tempel's Comet of 1 866. 

At one time the Leonids gave magnificent displays of shooting 
stars, and historical records of these have been found dating back 
to a.d. 902. In 1833 and again in 1866 the meteors of the Leonid 
shower fell like snowflakes, the whole sky being crossed with their 
streaks of light at the rate of hundreds a minute. Nowadays the 
shower is unlikely to produce more than a few meteors in an hour's 
watch, but this is still called a 'shower', because the number of 
meteors is above the average. In any case, the Leonids can be 


recognized by their swift streaks, and by tracing these backwards 
to the radiant above the Sickle of Leo. 

Orion. Prominent among the constellations in the south-east on a 
November night 

Begirt with many a blazing star 
Stands the great giant Algebar, 
Orion, hunter of the beast! 

This great star group is tilted to the left as it comes over the 
horizon. Orion seems to be very careful about the manner of his 
rising; he may be a giant, but there is one thing he fears - the 
Scorpion. It was a scorpion that put an end to his existence when 
he was down here on Earth, and even now, up there among the 
stars, Orion will never appear if the Scorpion is at all visible, and 
in the spring he disappears in the south-west before Scorpio rises in 
the east. 

Orion is always pictured as a giant who is warding off the attack 
of Taurus, the Bull. In the seventeenth and eighteenth centuries 
many star atlases were published which illustrated these constel- 
lation figures with a certain amount of artistic skill. Bayer, in 
1603, drew Orion with his back towards us, holding a club in his 
left hand, and with his head turned to the left - apparently ignoring 
Taurus completely. The atlas of Flamsteed, the first Astronomer 
Royal, produced some years later, has Orion looking at the Bull, 
and with his body turned towards us, his club in his right hand. 
These two atlases seem to have influenced all the others, and there 
are two rival lines of thought. You may have a left-handed Orion, 
looking the wrong way, with his sword strapped round the middle 
of his back; or, if you prefer, you can have a right-handed giant 
who is imminent danger of tripping over his sword or over the hare 
(Lepus) that sits at his feet. 




New Moon: December 4 Full Moon: December 19 

Solstice: December 21 

Mercury is at inferior conjunction on December 18, and will not be 

visible during the month. 

Venus is still a brilliant spectacle in the morning sky before sunrise, 

but it is now moving in to superior conjunction, and is much lower 

in the sky in the south-east, and visible for a shorter period before 


Planetary Orbits in December 

Mars now rises in the east before midnight, and will be seen below 
the figure of Leo. There is a rapid change in the brightness of the 
planet as its distance decreases (magnitude +1-0 to +0-3), and by 
the end of the year, when it is about 102 million miles from the 
Earth, it will be more than six times as bright as it was in August. 
Mars passes into Virgo at the end of December, and will be at 
opposition on 1965 March 9 on the borders of Leo and Virgo. 


Jupiter is a bright evening star, to be seen in the south in mid- 
evening. It is still moving retrograde, but reaches a stationary 
point in early January. Jupiter will be at opposition in 1965 Dec- 
ember, when it will be seen on the borders of Taurus and Gemini. 
Saturn is an evening star, setting before midnight in the south-west 
in Aquarius. The next opposition of Saturn occurs in 1965 Sep- 

A partial eclipse of the Sun on December 4 will be visible only in 
the north Pacific Ocean and bordering countries. 
A total eclipse of the Moon on December 19 will be visible in the 
British Isles, beginning about an hour before midnight. Totality 
lasts from 2 h 07 m to 3 h 07 m , and the eclipse ends at 4 h 15 m (seepage 

The length of the day. In astronomical circles it is generally unwise 
to refer to seasonal effects, such as the spring equinox or the 
winter solstice, without carefully defining these terms. There are 
many astronomers in the southern hemisphere, where the seasons 
are completely reversed, and to refer to the summer solstice when 
they are in the depths of winter is sometimes a little tactless. To the 
ordinary reader, the word solstice conveys very little, and perhaps 
this is why the word is avoided by the makers of diaries. Our 
pocket diaries may give the dates of the equinoxes, but the solstices 
are not mentioned; instead, the entry simply reads 'June 23, 
Longest Day' or 'December 21, Shortest Day'. This is, of course, 
equally objectionable to those who live south of the equator, and 
presumably these diaries are intended only for northern latitudes. 
The statement is then (at least in theory) perfectly correct, for it is 
necessarily true that the shortest day must occur when the Sun is at 
its lowest in the sky, that is, when it reaches its greatest southern 
declination at the solstice. In actual fact, however, the Sun is 
changing its declination so slowly at this time that the days are of 
equal length for about a week. What is much more noticeable is 
that at the end of December the evenings are already becoming 
lighter, while the Sun continues to rise later each morning. We may 
illustrate the fact with a table of times of sunrise and sunset for 
the present year (in latitude 52 degrees north), although the figures 


will not be more than a minute or so in error in any other year. 

Mean time 
Sunrise Appt.noon Sunset 

h m h m h m 



7 45 

11 49 

15 51 


7 52 

11 51 

15 50 


7 58 

11 53 

15 49 


8 03 

11 55 

15 49 


8 06 

11 57 

15 50 


8 07 

12 00 

15 53 


8 08 

12 02 

15 58 


8 08 

12 04 

16 04 


8 05 

12 07 

16 10 


8 01 

12 09 

16 18 

Apparent time 



h m 

h m 

7 56 

16 02 

8 01 

15 59 

8 05 

15 56 

8 08 

15 54 

8 09 

15 53 

8 07 

15 53 

8 06 

15 56 

8 04 

16 00 

7 58 

16 03 

7 52 

16 09 


The table shows that the time of sunrise continues to be later 
each day until the beginning of January, whereas the time of sunset 
has already reached its earliest in mid-December. Thus the familiar 
comment that 'the evenings are drawing out' is a simple statement 
of fact. The reason for this state of affairs is the rapid change in the 
equation of time at this season (see the note on 'The Sundial' on 
page 40). Sunrise and sunset are phenomena of the apparent Sun, 
but our clocks keep mean time, not apparent time, and we are 
accustomed to judge the time of noon by the clock, and not by the 
Sun. The third column in the table gives the mean time of apparent 
noon, and here we see the effect of the changing equation of time. 
The Sun is in the south, not at 12 o'clock, but at times which are 
growing later by about half a minute each day. The length of the 
morning (from sunrise to apparent noon) is equal to the length of 
the afternoon (from apparent noon to sunset), but the midpoint of 
the day, when the Sun is due south, is swinging over from bef ore- 
noon to after-noon. In the last two columns of the table the equa- 
tion of time has been added to the mean times of sunrise and sun- 
set, so as to give the apparent times of these phenomena. It will 
now be seen that the shortest day is indeed on December 21, the 
day of the solstice. 


Eclipses, 1964 

In 1964 there will be six eclipses, four of the Sun (all of which are 
partial eclipses), and two total eclipses of the Moon. Of these, only 
the two lunar eclipses are visible in the British Isles. 

1. A partial eclipse of the Sun on January 14, visible only in 
Antarctica, Tasmania and the southern point of South 
America. This eclipse belongs to a series which is moving 
north and increasing in magnitude. 

2. A partial eclipse of the Sun on June 10, visible only in 
Australia and New Zealand. This eclipse occurs at the end 
of a series which is moving south; the last total eclipse in the 
series was in 1910. 

3. A total eclipse of the Moon on the night of June 24, visible in 
the British Isles. The shadow of the Earth will first be seen at 
the extreme eastern limb of the Moon at 23 h 09 m , and it will 
appear to move to the right across the face of the Moon 
until total eclipse occurs shortly after midnight - June 25 at 
00 h 16 m . The Moon will then be due south, and the totality 
lasts for 100 minutes, ending at l h 57 m . The shadow con- 
tinues to move westwards, finally passing off the Moon at 
the west limb at 3 h 03 m . 

4. A partial eclipse of the Sun on July 9 is the third in a new 
series of eclipses which first appeared in 1928. The series is 
moving south, and this eclipse is visible only in Arctic 

5. A partial eclipse of the Sun on December 4 will be visible in 
eastern Asia, the north Pacific Ocean and Alaska. It occurs 
at the end of a series which is moving north and decreasing 
in magnitude. 

6. A total eclipse of the Moon on December 19 will also be 
visible in the British Isles. The umbra of the Earth's shadow 
makes its first contact with the eastern limb of the Moon at 
h 59 m , and will move to the right across the Moon's face. 
Totality commences at 2 h 07 m and lasts for an hour, ending 
at 3 h 07 m The shadow passes off the west limb at 4 h 15 m . 



In the course of its journey round the sky each month, the Moon 
passes in front of all the stars in its path, and the timing of these 
occultations is useful in fixing the position and motion of the 
Moon. The Moon's orbit is tilted at more than 5 degrees to the 
ecliptic, but it is not fixed in space. It twists steadily westwards at 
the rate of about 20 degrees a year, a complete revolution taking 
18-6 years, during which time all the stars that lie within about 
6 J degrees of the ecliptic will be occulted. The occultations of any 
one star continue month after month until the Moon's path has 
twisted away from the star, but only a few of these occultations 
will be visible at any one place in hours of darkness. 

There are only four first-magnitude stars that can be occulted 
by the Moon; these are Regulus, Aldebaran, Spica and Antares. In 
1964, however, the Moon's path is in such a position that it passes 
north of all four stars, and they cannot therefore be occulted. 

The planets Mercury, Venus and Mars are all occulted by the 
Moon in 1964, but these phenomena will not be visible in the 
British Isles. 

Details of occultations of the planets, and of all stars down to 
magnitude 7-5, as well as possible occultations of stars by planets, 
are published in the annual Handbook of the British Astronomical 

Comets in 1964 

The appearance of a bright comet is a rare event which can never 
be predicted in advance, because this class of object travels round 
the sun in an enormous orbit with a period which may well be 
many thousands of years. There are therefore no records of the 
previous appearances of these bodies, and we are unable to follow 
their wanderings through space. The comets of short period, on 
the other hand, return at regular intervals, and attract a good deal 
of attention. Unfortunately they are all faint objects, and are 
recovered and followed by photographic methods, using large 



telescopes. Most of these short-period comets travel in orbits 
which carry them out to the orbit of Jupiter, and it is this planet 
which is responsible for the severe perturbations which many of 
these comets undergo. In 1964 the following short-period comets 
are expected to return to perihelion: 

Comet Encke, which has the shortest period of any known 
comet (3-3 years), is named after the famous mathematician who 
first computed its orbit. Encke was able to show that the comet of 
1818, discovered by Pons, was the same as Mechain's comet 
of 1 786, with Caroline Herschel's of 1 795, and with Pons's comet of 
1805, and he predicted another return in 1822. This was the second 
instance of a predicted return, that of Halley's comet in 1759 being 
the first. Encke's comet has been seen at forty-six returns to the 
Sun and is expected in 1964 May. 

Comet Pons-Winnecke has been seen at fifteen previous peri- 
helion passages since its discovery in 1819. It has a period of about 
6-1 years and is greatly perturbed by Jupiter at alternate revolu- 
tions. It was not seen in 1957, but is expected at perihelion in 1964 
March. As a result of the perturbations the orbit is growing larger 
and less eccentric, while the inclination is increasing. 

Comet Kopff, last seen in 1958, was discovered in 1906 and has 
made eight appearances. It has a period of 6-3 years and is due to 
return in 1964 May. 

Comet Daniel was discovered in 1909, but has been seen since 
then only at the 1937, 1943 and 1950 returns. It has a period of 6-7 
years and is due at perihelion in 1964 April. 

Comet Arend-Rigaux was discovered by two Belgian astrono- 
mers in 1950, and was also seen at the 1957 return; it is predicted 
to return to perihelion in 1964 June. 

Comet Shajn-Schaldach is also due in 1964 June. It was dis- 
covered independently by Mrs. P. Shajn at the Simeis Observatory, 
Crimea, and by Robert D. Schaldach at the Lowell Observatory, 
Flagstaff, Arizona, in 1949, but it was missed in 1958. If the com- 
puted orbit is correct, this comet has a period of 7-3 years, and its 
next perihelion passage is in 1964 June. 

Comet Honda-Mrkos-Pajdusakova was discovered in 1948, and 


was seen in 1954 but not in 1958. It has a short period of 5-2 years. 

Comet Wolf-Harrington is an example of a comet that was 
thought to be a new one, but was found to have been seen pre- 
viously. Harrington discovered this comet in 1951 on the sky 
survey plates taken at Mount Palomar Observatory, but it appears 
to be identical with comet Wolf (1) seen only at one previous 
return in 1924. The comet was observed in 1958. 

Comets Schwassmann-Wachmann (1) and Oterma are visible 
every year because they travel round the Sun in orbits which are 
much more nearly circular than those of most other comets. 
Comet Schwassmann-Wachmann has an orbit with a period of 16 
years which lies entirely between the orbits of Jupiter and Saturn. 
It undergoes remarkable changes of brightness, which seem to have 
some connexion with solar activity. Comet Oterma has a smaller 
orbit, lying between those of Mars and Jupiter, and resembling the 
orbits of certain minor planets. The period at present is nearly 8 
years, but Miss L. Oterma has shown that the comet will make a 
close approach to Jupiter in 1962-64, and this will cause the orbit 
to become much larger and more eccentric, with a period of 19 
years. As a result the comet will only be visible in large telescopes 
in future years, because its perihelion distance will have increased 
from 3-4 to 5-3 astronomical units. 


Meteors ('shooting stars') may be seen on any clear moonless 
night, but on certain nights of the year their number increases 
noticeably. This occurs when the Earth chances to intersect the 
orbit of a meteor swarm, which is a concentration of meteoric dust 
moving in an orbit around the Sun. Such an intersection can occur 
only at one particular time of year, but if the dust is spread out 
along the orbit, the resulting shower of meteors may last for 
several days. The word 'shower' must not be misinterpreted - only 
on very rare occasions have the meteors fallen so fast as to resem- 
ble snowflakes falling. 

The naked-eye study of meteors is quite a laborious task, but 


even a casual observer, watching for, say, ten minutes on an 
August night, may observe a number of Perseids. If their tracks 
are marked on a star map, and traced backwards, a number of 
them will be found to intersect in a point (or a small area of the 
sky) which marks the radiant of the shower. This gives the direc- 
tion from which the meteors have come. 

The following table gives some of the more easily observed 
showers, with their radiants; the effect of moonlight in 1964 is 

Limiting dates Shower Maximum R.A. Dec. Note 

Jan. 3-4 Quadrantids Jan. 3 15 h 28 m +50° 

April 20-22 Lyrids April 22 18 h 04 m +33° 

July 27-Aug. 17 Perseids Aug. 12 3 h 04 m +58° 

Oct. 15-25 Orionids Oct. 20-21 6 h 24 m +15° M 

Oct. 26-Nov. 16 Taurids Nov. 1-7 3 h 36 m +14° 

Nov. 15-17 Leonids Nov. 16 10 h 08 m +22° M 

Dec. 9-14 Geminids Dec. 13 7 h 28 m +32° 

Dec. 20-22 Ursids Dec. 22 14 h 28 m +76° M 

M= moonlight interferes 

Minor Planets in 1964 

Of the 1,600 minor planets which are listed in the catalogues, only 
the 'big four', Ceres, Pallas, Juno and Vesta, can reach any con- 
siderable brightness, and only the last of these, Vesta, can occasion- 
ally be seen with the naked eye. This may happen in 1964 at the 
time of opposition on September 2, when Vesta is in Aquarius, 
some degrees south-east of Saturn, and about 12 degrees north of 
the first-magnitude star Fomalhaut. 

The planets Pallas and Juno both come to opposition on May 
18, but are widely separated in the sky, Pallas being well north in 
Hercules, while Juno is on the borders of Libra and Serpens. Ceres 
is in opposition on June 21 in Sagittarius, and at this time may 
reach the seventh magnitude. 


Some Events of 1965 


In 1965 there will be three eclipses, two of the Sun and one of the 
Moon ; in addition there will be a penumbral lunar eclipse. 

May 30 - a total eclipse of the Sun, visible in the south Pacific. 
June 14 - a partial eclipse of the Moon, visible in the British 

Nov. 23 - an annular eclipse of the Sun, visible in India, Borneo 

and New Guinea. 
Dec. 8 - a penumbral eclipse of the Moon. 


Mercury may best be seen as an evening star at eastern elonga- 
tion on March 21, and as a morning star at western elonga- 
tion on September 2. 

Venus will not be a very conspicuous object until the end of the 
year; it comes to greatest elongation as an evening star on 
November 1 5, and is at greatest brilliancy on December 21 . 

Mars will be in opposition on March 9, reaching magnitude 
— 1-0 among the stars of Leo. Conditions will be much the 
same as in 1963, with Mars at a distance of 62 million miles, 
but farther south in the sky. 

Jupiter is in conjunction on May 30, and at opposition on 
December 18 on the borders of Taurus and Gemini. 

Saturn will be in conjunction on February 26 and at opposition 
on September 6 in Aquarius. 

Uranus will be at opposition on March 3 and Pluto on March 5, 
both planets being in Leo ; Neptune is at opposition on May 
9 in Libra. 

The Distance of the Sun 


The advent of space research, and particularly the launching of 
interplanetary probes, has created a demand for a more precise 
knowledge of the actual distances between the planets. These 
distances are measured by the astronomer in terms of the astro- 
nomical unit, which may be regarded as the mean distance from 
the Earth to the Sun, but the actual length of this unit in miles or 
kilometres is of little interest to him ; he is more concerned with 
angles, or proportions, than with actual distances. It is only in 
those cases where the size of the Earth enters into his calculations 
that any use is made of the distances. For example, in dealing with 
eclipses, the lengths of the shadows of the Earth and Moon are 
required, and the Sun's distance must therefore be included in the 
calculations. Yet even here it is used in the form of an angle - in 
this case it is the solar parallax, which is the angle subtended by 
the equatorial radius of the Earth at the distance of the Sun. This 
is a very small quantity, amounting to only a few seconds of arc, 
and as it plays only a minor part in these calculations, it is 
sufficient to have its value known to three-figure accuracy. Thus 
in the Astronomical Ephemeris, the value of the solar parallax is 
taken as 8 "-80, and although it is known that this is not precisely 
correct, it suffices for this type of work. 

In most astronomical studies the actual scale of the solar system 
does not matter - it is the proportions that are important. Now, 
the proportions of the mean distances of the planets from the Sun 
are known with great accuracy, because the time of revolution of a 
planet about the Sun is related to its distance from that body 
through Kepler's third law (this states that the square of the period 


in years is equal to the cube of the distance in astronomical units). 
In this way we can prepare a very accurate map of the whole solar 
system, but the precise scale of that map is not known with 
sufficient precision to please the space scientists. 

Additional errors arise from the fact that the positions of the 
planet as given in the Ephemeris are based on theories which are 
already more than sixty years old, and although recent improve- 
ments have been made by Duncombe (for Venus) and Clemence 
(for Mars) these have not yet been generally adopted. Thus we 
have the situation that the distances of the planets, given in the 
Ephemeris to seven places of decimals (in astronomical units), are 
not really known to such accuracy; in fact, it is doubtful if we 
know the positions of any of them to better than five decimals, or, 
say, the nearest thousand miles. Clearly, for space research some- 
thing better is needed, but the determination of these distances by 
astronomical methods is no easy matter. 

The first attempt was made by Aristarchus more than 2,000 
years ago, by measuring the angles between the Sun and Moon at 
First Quarter. This is very difficult to do successfully, and his result 
was that the Sun was only twenty times as far away as the Moon. 
Ptolemy used a similar method with eclipses, and found a value for 
the Sun's distance of 1,200 times the radius of the Earth; this is 
equivalent to about 4£ million miles, but such was the authority of 
Ptolemy that this value was used without question for the next 
1 ,500 years. In the sixteenth century Kepler and his contemporaries 
knew that this value was too small. Huygens, for example, guessed 
that 12,000 Earth radii was a better answer, but it was Cassini who 
first obtained a reasonable result. He used observations of Mars, 
sending one of his assistants to the new colony of Cayenne, while 
he himself observed in Paris. The two stations would see Mars in 
slightly different directions, and the difference between them could 
be used to calculate the distance of Mars. Since the proportions of 
the planetary orbits are known very accurately, a measure of the 
distance between any two of them gives at once the scale of the 
whole system, and this method, first used by Cassini, is the basis 
of all subsequent astronomical measurements. Cassini's result for 


the Sun's distance was 86 million miles, which is about 7 per cent 
too small. 

In the next century, acting on a suggestion made by Halley, 
attempts were made to measure the distance of the planet Venus 
on the rare occasions when it passes across the face of the Sun. 
Although great preparations were made, the results were dis- 
appointing, because Venus has a dense atmosphere, and as it 
transits the face of the Sun, it has no sharp outline, while at the 
time of contact with the edge of the Sun, the planet seems to be 
surrounded with a bright aura, and it is impossible to time the 
exact moment of contact. However, the results were worked up, 
not only in 1761, but also again at the transit of Venus in 1769, 
and a value of the Sun's distance of 95,370,000 miles was obtained; 
this value was used for more than thirty years in the middle of the 
following century. Many astronomers were far from happy about 
this result. For example, Hansen, dealing with the motion of the 
Moon, pointed out that it was quite impossible to account for the 
position of the Moon near First and Last Quarter if this value were 
used, and he suggested that it should be about 3 per cent smaller. 

Towards the end of the nineteenth century the distance was 
measured by Cassini's method, but some of the minor planets were 
used instead of the planet Mars. These are so small that they look 
like stars, so that their positions are more easily measured; also 
they are not coloured, and they come closer to the Earth than any 
of the major planets. The results from these measurements, using 
the planets Victoria, Iris and Sappho, were in good accordance, 
and gave a value of 8"-80 for the solar parallax, corresponding to 
a distance of 92,890,000 miles for the Sun's distance; this value 
has been used in the Ephemeris since 1900. At the opposition of 
the small planet Eros in 1931, when it came within 16 million miles 
of the earth, a great campaign was organized to establish a better 
value for the astronomical unit. The improvements in instruments, 
the use of photography, and the large number of observations, all 
combined to make this a more reliable value. In all, forty-four 
observatories from all parts of the world took part, and the 
resulting calculations, which took ten years to complete, gave a 


value of 8"-790 for the solar parallax, corresponding to a distance 
of 93,005,000 miles. 

In recent years a re-discussion of the Eros campaign has been 
made by Rabe, of Cincinnati Observatory, who used all the 
additional knowledge acquired in the intervening twenty years to 
deduce an improved value of 8"-7984 (92,911,000 miles), and this 
may be accepted as the best value that astronomical methods can 
obtain. Even here, the last figure may be several units in error, so 
that this does not give a value for the Sun's distance to an accuracy 
better than about one part in 20,000. None of these astronomical 
methods is a direct measurement, but is actually a deduction from 
the laws of celestial mechanics. It is only in recent years that direct 
measurements of the distance of a planet have been made by 
radar, and all of these have been applied to Venus at the time of 
inferior conjunction. The latest and most detailed of these experi- 
ments was carried out at the April 1961 conjunction of Venus by 
the staff of the Jet Propulsion Laboratory of the California 
Institute of Technology, Pasadena. 

The transmitting and receiving antennas have similar parabolic 
reflectors 85 feet in diameter, and these are placed about seven 
miles apart at Goldstone, near Barstow, California. The trans- 
mitter, with a power of 10 kilowatts, used a frequency of 2,388 
megacycles (wave-length 12-5 centimetres), which was controlled 
to better than one part in 10 10 by a crystal oscillator locked to a 
caesium resonator. Two entirely different techniques were employed, 
in one of which the actual distance of Venus was measured by the 
time taken for the propagation of the radio signal to and from the 
planet ; the other method used the Doppler shift in wave-length due 
to the relative velocities of the Earth and Venus. Since measure- 
ments of the Doppler effect give a value for the velocity of the 
planet towards or away from the Earth, they are most effective 
before or after inferior conjunction, and the experiments were 
continued from March 10 to May 10. At the conjunction itself, 
when the planet is moving on a course almost parallel with that of 
the Earth, the Doppler method is less valuable, and it is here that 
the range method is used. Even at its closest (about 26 million 


miles) the time taken for the radio pulses to reach Venus and be 
reflected back to the receiver is nearly five minutes, and the signals 
were therefore coded in such a way that they could be identified. 
Five variations of the two methods were used in conjunction with 
the latest improved values for the positions and velocities of Venus 
and the Earth, derived from Duncombe's theory. 

The five sets of results were remarkably consistent, and gave a 
final mean value of 8"-7940976 for the solar parallax, correspond- 
ing to a distance from the Earth to the Sun of 92,956,530 miles, 
with an estimated probable error of about 150 miles. The results 
are strongly confirmed by independent measurements made at the 
same conjunction of Venus by the Millstone Radar Observatory 
of the Lincoln Laboratory, Massachusetts Institute of Technology. 
Using a very different wave-length of 68 centimetres, they obtained 
a value of 149,597,700 kilometres, or 92,955,820 miles, in remark- 
able agreement with the J.P.L. values. The consistency of these 
results is so good that astronomers interested in the subject have 
been greatly impressed. The discrepancy between Rabe's results 
and those of the radar measurements has yet to be explained, and 
it will certainly be necessary to repeat the measurements many 
times, using, if possible, oppositions of Mars as well as future con- 
junctions of Venus. If successive results under differing conditions 
continue to give a similar value for the astronomical unit, then 
this will undoubtedly have to be accepted as the standard figure. 

With Mariner 2 to Venus 


On 1962 December 14 another goal in the exploration of space was 
reached when the first successful planetary probe, Mariner 2, flew 
to within 21,600 miles of the planet Venus. It was hoped that the 
probe would clear up some of the mysteries which surround the 
planet, but unfortunately it seems to have created many more 
questions. Many astronomers thought that Venus was not too 
different from the Earth. Even if Mariner's findings are not 
absolutely correct, it has shown that the planet bears very little 
resemblance to its 'twin' and that it is not a very hospitable place 
for an interplanetary traveller ! 

The Mariner project was developed for the National Aero- 
nautics and Space Administration by the Jet Propulsion Labora- 
tory of the Californian Institute of Technology. Within nine 
months from concept, two 'Mariners' had been constructed, tested 
and delivered to Cape Canaveral for launching, a feat that could 
not have been achieved without the dedication of all the scientists 
and technicians associated with the project. The first launch ended 
in failure when a fault in the ground support equipment forced the 
range safety officer to destroy the rocket just after launching. Suc- 
cess, however, came on August 27, when the second probe was 
launched. Apart from a few minor incidents, everything went 
according to plan. Information was sent back continually during 
the three months' journey to the planet, and even after it had 
passed Venus it still continued to send back information for 
another three weeks. 

The Experiments 

Mariner weighed 447 lb, but the scientific experiments accounted 


for only 41 lb. Excluding the solar panels and the high gain aerial, 
it measured 5£ feet across and nearly 10 feet high. In the cruise 
position, with the solar panels extended, it was 16| feet across. 
The hexagonal base housed the batteries, computers, the rocket 
motor for the mid-course correction and the radio equipment. The 
omnidirectional aerial was fixed at the top of the superstructure, 
whereas the highly directional aerial was hinged mounted to the 
base of the hexagon. Mounted at various points on the tubular 
superstructure were the instruments required for the scientific 

The probe contained six experiments, two of which were 
designed to operate only when the spacecraft flew by the planet. 
One of these, the microwave experiment, was designed to give 
information on the atmosphere of Venus and also on the surface 
temperature of the planet. This was done by recording the inten- 
sity of the radiation at 13-5- and 19-millimetre wavelengths. These 
two wavelengths were chosen because the former is located in the 
water vapour absorption band, whereas the latter is unaffected by 
the presence of water vapour. The 19-millimetre radiation in 
addition to measuring the surface temperature of the planet, could 
also test the two theories regarding the atmosphere of Venus by 
detecting the presence of either 'limb darkening' or 'limb brighten- 
ing'. The latter would confirm the presence of a dense ionosphere, 
whereas the former would show that the source of the radiation 
was the surface of the planet. 

It was planned to turn on the experiment 10 hours before the 
encounter with the planet. The radiometer, which was nothing 
more than a 20-inch radio telescope, would scan up and down over 
an angle of 120 degrees at a rate of 1 degree per second. As soon as 
Venus had been located, the scan rate would drop to 1/10 degree 
per second. In addition, a special command system was built in so 
that as soon as the edge of the planet was reached the direction of 
the scan was reversed. Once located, the planet would be under 
continual observation. The lateral movement across the surface of 
the planet was achieved by the motion of Mariner as it flew by the 


The complementary experiment, using an infra-red radiometer, 
attached to the side of the microwave aerial, involved two wave- 
lengths in the 8-5 and 10-4 micron region. The latter is 
absorbed by carbon dioxide, whilst the former is unaffected by 
the presence of this gas. Neither of these will, however, pass 
through cloud. A difference in the signal strength would give 
information regarding the carbon dioxide content in the atmo- 
sphere and in addition a varying signal strength from different 
parts of the planet would indicate the presence of breaks in the 
cloud layer. 

The magnetometer experiment was designed to measure the 
strength and direction of the interplanetary magnetic field and also 
(if it existed) the magnetic field associated with Venus. The appara- 
tus was mounted just below the onmidirectional aerial so as to be 
as far away as possible from any possible interference from other 
equipment on board the spacecraft. 

The concentration and energy of interplanetary dust was deter- 
mined using a cosmic dust detector. This consisted of a sounding 
board 10 inches by 5 inches. The number of dust particles striking 
the plate was recorded via a microphone mounted in the centre 
of the plate. There were two counters, one for high-momentum and 
the other for low-momentum particles. 

The two other experiments involved the detection of high- and 
low-energy particles which are known to exist in large quantities in 
interplanetary space. The high-energy radiation experiment con- 
sisted of an ionization chamber and three Geiger-Miiller counters. 
A knowledge of the concentration of these cosmic rays in regions 
well away from the Earth, and a knowledge of the way this concen- 
tration varied with solar activity, is vital for the understanding of 
the rather complicated changes in the character of the radiation 
reaching the Earth's surface. The solar plasma detector was 
designed to give information about the charged particles that are 
continuously being emitted by the Sun, the so-called solar wind. It 
consisted of a curved tunnel containing two plates, one negatively 
and the other positively charged. A charged solar particle is 
attracted by one plate but repelled by the other, and so it will 


follow a curved path down the curved tunnel. Only those particles 
having the right speed will reach the end of the tunnel and enter a 
charged collecting cup. By varying the voltage on the plates, it was 
possible to collect details of the numbers of particles over a large 
energy range. 

The Journey to Venus 

The placing of Mariner on the course which took it to Venus 
consisted of three distinct operations. The Atlas booster rose 
vertically from Cape Canaveral and pitched over in the direction 
of South Africa. The Agena second stage fired for the first time and 
put the Agena-Mariner combination into a parking orbit with a 
speed of 18,000 mph at a height of 115 miles above the Earth's 
surface. Just before reaching the African coast, the Agena fired for 
the second time and boosted the speed to 25,503 mph, that is, about 
850 mph above the escape velocity for that altitude. The probe 
therefore moved away from the Earth in a hyperbolic orbit. At the 
same time as it moved away from the Earth, it was slowed down by 
the Earth's gravitational pull, and by the time it had reached a 
distance of about 600,000 miles, the velocity had fallen to 6,874 
mph. At this point it can be assumed that the probe had escaped 
from the Earth. The second-stage firing was timed so that the 
probe moved away in the opposite direction to that of the Earth's 
motion round the Sun. Mariner was therefore travelling round the 
Sun 6,784 mph slower than the Earth (approx. 66,000 mph) and 
could not therefore maintain a circular orbit against the Sun's 
gravitational pull. It consequently fell inwards towards the orbit of 
Venus. As it moved inwards it speeded up and by the time it 
passed between the Sun and Venus, it was travelling at 91,000 mph 
against Venus's orbital speed of 78,000 mph. Its path in the vicinity 
of Venus was designed so that the planet would not block the 
probe's view of the Earth. 

Two minutes after reaching the peak velocity of 25,503 mph, 
the Agena rocket separated from the probe, rotated through an 
angle of 140 degrees and fired again, thus performing a retro- 
manoeuvre to put it on an entirely different orbit. This was done to 


prevent the rocket from hitting Venus and also to prevent the 
spacecraft's optical system from confusing the Agena with the 
Earth or the Sun. Separation caused the spacecraft to tumble, but 
this was cancelled, using a gas stabilization system. Contact with 
the Earth was achieved via the omnidirectional aerial, and all 
communications with the probe were handled by the command 
subsystem. This decoded the incoming signals and sent them to the 
designated subsystem. It also coded the data obtained from the 
probe's instruments ready for transmission back to the Earth. The 
issuing of the commands to the spacecraft were handled by a digital 
Central Computer and Sequencer (CC and S). The CC and S was 
responsible for the launch sequences, the mid-course correction 
and the Venus encounter sequence. 

The first command issued by the CC and S took place 49 
minutes after launch when the solar panels were opened out and 
the radiometer unlocked. At launch +60, the CC and S instructed 
the probe to find the Sun. Sun sensors, linked to valves controlling 
gas jets, moved the probe until the solar panels were pointing 
directly at the Sun. To conserve gas, a tolerance of \ degree was 
allowed. After 7 days, the CC and S issued commands for the 
highly directional aerial to find the Earth. This was done by rotat- 
ing the probe about its longitudinal axis until the aerial pointed 
directly at the Earth. If the Earth sensors had mistaken the Moon 
for the Earth, an overriding command would have been sent from 
the Earth to reject this and continue searching. As soon as the 
Earth had been acquired, all transmissions via the omnidirectional 
aerial were stopped. 

It was soon apparent that the path taken by the probe was not 
exactly that required to give a fly-by of 10,000 miles. In fact, it 
would have missed Venus by well over a quarter of a million miles. 
Instructions were sent from the Deep Space Instrumentation 
Facility at Goldstone, California, giving the direction and amount 
of roll and pitch required and also the amount of velocity incre- 
ment needed. These were stored in the CC and S until Goldstone 
transmitted the 'go' signal. This order was given on September 4. 
The following sequences of events illustrate the complexity of the 


manoeuvre. Thirty minutes before the calculated time the stabiliz- 
ing gyros were switched on. The Earth sensors were then switched 
off and the aerial moved out of the way of the motor exhaust. After 
the roll and pitch manoeuvres had been carried out, the probe was 
given 2 minutes to settle down. The mid-course motor was then 
turned on. Because the attitude control gas jets were not sufficiently 
powerful to maintain stability, this was achieved by using movable 
jet vanes extending into the motor exhaust. The motor was so 
precise that it could burn for as little as 50 milliseconds and could 
increase the velocity by as little as 0-7 feet/second or as much as 
187 feet/second. Mariner then went through the Sun and Earth 
acquisition sequences for the second time. 

The result of this manoeuvre corrected the path to nearly the 
required value. The smallness of the error is illustrated by the fact 
that the probe flew by Venus at a distance of 21,594 miles, which is 
only a little greater than the planned figure. 

The 109-day journey to Venus brought one or two anxious 
moments. In the early stages the Earth sensors did not appear to 
be behaving normally, but this problem cleared itself when the 
sensitivity suddenly rose to the predicted level. On November 15 a 
short circuit developed in one of the solar panels, reducing the 
amount of power available. The scientific instruments were 
switched off to conserve power, but the short circuit healed itself 
and full power was restored. A week later the trouble returned, 
but fortunately there was still sufficient power available. 

Although increasing temperatures brought one or two anxious 
moments, the biggest headache occurred just prior to the planet 
encounter. The CC and S had been programmed to activate the 
scanners 10 hours before the nearest approach. At the appointed 
time nothing happened ! The scientists waited several hours to see 
if the switch-on would occur after the computer had gone through 
another cycle of operations, but still nothing happened. For- 
tunately, provision had been made for the probe to obey signals 
from the Earth, and when this signal was given Mariner responded 
and the radiometers started scanning. Contact with the planet 
lasted for 42 minutes and then Mariner went back to its 'cruise' 


mode and sent back information on conditions in space for 
another 20 days. 

The Results 

The first news conference giving details of the information 
gained by Mariner as it flew by Venus was held on 1963 February 
26. Although most of the 65 million pieces of information sent 
back by the probe was in the hands of the scientists responsible for 
the experiments within half an hour of reception back on Earth, it 
took two months to interpret this information. The main reason 
for this delay was an unexpected difficulty in interpretation due to 
circuit interaction between the various components. This was 
unfortunately most serious in the microwave and infra-red experi- 
ments. The data have still to be fully analysed, but it is not expected 
that the provisional results will be modified to any large degree. 

As Mariner passed between the Sun and Venus, the radiometers 
made three very useful scans of the planet. The first went upwards 
on the dark side, the second downwards approximately along the 
terminator, that is the boundary between the dark and sunlit sides 
of the planet. In fact, the terminator was crossed at one point. The 
third scan went upwards over the sunlit side, passing very close to 
the point directly under the Sun. 

The full analysis of the returns from the microwave experiment 
has still to be made, because the sensitivity of the 13-5 millimetre 
channel behaved in a rather unexpected manner and this has caused 
a delay in interpreting the information. The 19-millimetre channel, 
however, has indicated that the surface temperature on both the 
sunlit and dark sides is roughly the same. It also showed that there 
is very strong 'limb darkening'. This infers that the surface tem- 
perature is very hot ; in fact, a figure of 800° F. has been given. 

The strength of the radiation received on the two infra-red 
channels was more or less the same, indicating that the atmosphere 
above the cloud layer contains no (or at the most, very little) carbon 
dioxide. The temperature at the top of the cloud layer is apparently 
the same on both the dark and sunlit sides ; it also appears to be 
uniform except for one local area near the southern end of the 



terminator. At this point, the temperature seems to be 20° lower 
than the rest of the cloud. The cloud layer seems to be uniformly 
distributed with no breaks in it. As with the microwave experiment, 
there was strong 'limb darkening'. This has been explained by the 
fact that radiation from the centre of the disk comes from lower 
down in the cloud layer than that coming from the limb. The tem- 
perature of the top of the cloud is given as —60° F. but a little way 
in it rises to — 30° F. 

During the fly-by the magnetometer did not behave in any way 
different from that recorded during quiet periods on the journey to 
Venus. From this, it was concluded that the magnetic field associ- 
ated with the planet, if indeed it has one, is very much weaker 
than that of the Earth. This result was confirmed by the ion 
chamber particle detector, which it was hoped would detect the 
equivalent Van Allen radiation belts round Venus. No such belts 
were detected and it was therefore concluded that Venus has a 
negligible magnetic field. 

Mariner's picture of Venus does not fit in very well with the 
pictures painted from observations made back on Earth. Spectro- 
scopic evidence indicates the presence of carbon dioxide in the 
atmosphere, but it may well exist in the region below the cloud 
layer, a region not investigated by Mariner. The surface tempera- 
ture is much higher than the terrestrial observations seem to 
indicate. What is surprising is the lack of a magnetic field, although 
some astronomers had previously thought that this may be the 
case. Nevertheless, it had been noticed that when Venus lay be- 
tween the Earth and the Sun, there was a reduction in the number 
of disturbances caused by solar plasma. This seemed to indicate a 
shielding effect due to a magnetic field associated with Venus. 

The 'cold spot' detected by the infra-red radiometer has not yet 
been explained. It could be that the cloud is a little higher at this 
point and is therefore colder, or it could be due to some surface 
feature. Radar experiments, conducted whilst Mariner was on its 
way to Venus, have detected a small patch on the planet which 
seems to be different from the rest of the surface. It seems to be in 
the same general area, but because of the uncertainty of the 


position of the axis of rotation, it is not possible to say whether it 
is the same feature or not. 

A very big mystery surrounding Venus is its rate of rotation. 
Many values have been put forward, one of the latest being the 
value obtained from the radar experiments mentioned earlier. This 
suggests that Venus rotates in a retrograde manner relative to the 
Sun, but it is non-rotating relative to the stars. This would mean 
that the Sun would rise in the west and set in the east about 110 
days later. If this is correct, many problems are created to explain 
the similarity of the temperatures on the dark and sunlit sides. It 
seems to indicate a very strong 'greenhouse eifect' and also a 
violent circulation of the atmosphere below the cloud layer. 

A very big factor for the success of the project was the very 
accurate tracking of the probe. Its speed was known to within 0-01 
mph relative to the Earth. By noting the changes in its velocity as 
it passed Venus, a new figure for the mass of the planet was 
obtained, viz. 0-81485 times that of the Earth. No doubt, when the 
final figures have been declared, astronomers will have a much 
more accurate figure for the astronomical unit, i.e. the distance of 
the Earth from the Sun. 


On 1963 January 4 at 14 h , 130 days after launch, contact was 
lost and the experiment came to an end. At that time the probe 
was 54,000,000 miles from the Earth. Thus ended the first success- 
ful interplanetary space probe. Even if its findings were not what 
many people hoped and even if these findings are subsequently 
found to be in error, its place in the history of science and tech- 
nology is assured. 

Selenology -or Geology Applied to the 


The Moon, since it has no atmosphere and lies in such close 
proximity to the Earth, has attracted the attention of great num- 
bers of astronomers since the science received the benefit of the 
telescope. Indeed, it would not be an exaggeration to say that 
many lunar observers have a more detailed knowledge of the 
Moon's surface than they have of the Earth itself. With a 3-inch 
refracting telescope, craters but 3 miles in diameter can be resolved, 
and consequently a great amount and variety of features await the 
attention of lunar observers. 

The most obvious features of the lunar surface are the vast 
dark maria. These contrast strongly with the bright walls of the 
thousands of craters surrounding them and lying on their surfaces. 
Long chains of small craters, rifts and mountain blocks are also 
prominent among the structures present on the Moon. From the 
earliest times in the history of observational astronomy, astrono- 
mers have indulged in a controversy as to the possible origin of 
the major lunar forms. One school of thought favours meteorites 
as the cause of the craters, whilst the other opposing school finds it 
expedient to reconcile them to the terrestrial volcanoes. It is the 
opinion of the present author that the latter mode of origin is the 
most likely to be proved when man sets foot on the lunar surface. 

What, then, of the features to be seen on the Moon and how can 
their structure be explained by geological processes known on the 
Earth? First of all, the craters. These are the most numerous of all 
lunar forms and range in size from mere pits, a matter of yards 
across, to huge sunken formations exceeding 180 miles in diameter. 
A study of the larger formations reveals that structurally they are 


much like the largest of Earth's volcanic 'subsidence cauldrons'. 
Characteristically these exhibit faulting, or collapse along their 
margins, this having occurred sometime after the actual eruption 
had taken place. This is due to the fact that such an area is quite 
unstable after the eruption and planes of weakness about the struc- 
ture bring about the collapse of the whole by faulting, so that a 
vast cauldron-like area is formed. The lunar walled plains clearly 
show this phenomenon, the walls in most cases being quite com- 
plex in form and much faulted. Erosion by subsequent mobile 
lavas has in some cases also contributed to further destruction of 
the initial features. 

Within the ramparts of the larger walled plains are found a 
variety of features, the great majority of which are younger in age. 
Presumably when the Moon was young the energy available for 
producing eruption features was at a maximum, and this slowly 
decreased as time went on. Thus the progressively younger features 
exhibited a gradual decrease in size, corresponding to the weaker 
forces coming from the interior. On the floor of Bailly, the largest 
of all lunar formations directly visible from the Earth, are found a 
number of smaller craters, some being very deep, hills, depressions, 
valleys and numerous minor features. The occurrence of such 
forms within the walled plains is interesting in that it shows a close 
agreement with those structures found inside subsidence cauldrons 
on the Earth. Often after the collapse of an earlier composite 
structure, a new vent gives rise to another eruptive phase in which 
one or more smaller craters are built up by the spilling out of lava 
or the throwing out of fragmentary lava, country rock and so on. 
Some of the seemingly isolated hill masses found may be the last 
remains of earlier cauldrons which were destroyed on the forma- 
tion of the last caldera ; others might be plugs or spines of especially 
viscous lava rich in silica, although this last point is rather contro- 

So far it is apparent that there seems to be an analogy between 
lunar and terrestrial structures. However, it has been argued that 
the size of the lunar walled plains is far in excess of the calderas of 
the Earth and so a comparison cannot be strictly made. It is true 


that the larger lunar formations have diameters in excess of 120 
miles, while the majority have diameters within the limiting range 
25 to 60 miles. On the other hand, terrestrial calderas rarely exceed 
60 miles in diameter and generally lie between 10 and 15 miles. It 
must be borne in mind, however, that the Moon's gravitational 
potential is only one quarter that of the Earth, and consequently 
much larger eruption features could be produced. In fact, it seems 
quite likely that on the whole lunar eruptions were less violent 
than those experienced on the Earth. 

Another prominent feature of the lunar surface is the preferred 
distribution of craters and valleys in certain directions, and the 
occurrence of numerous small craters along the limiting walls of 
large walled plains. The latter phenomenon can be quite simply 
explained. Remembering that it is most probable that the walls of 
the larger formations represent lines of slippage and faulting, and 
knowing that eruptions occur preferentially along lines of weak- 
ness in the crust, then it is not surprising that a large number of 
later craters are located along boundaries of walled-plains. A case 
in point is the large ruined formation Horbiger 1 (see Fig. 1) along 
whose south-eastern rampart is located a row of smaller craters. 
This continues farther east towards the adjacent smaller plain 
Pitatus, along whose walls are also found smaller craters and 
valleys. On the floor of the large formation Clavius, which lies 
near the lunar South Pole, is a series of craters which are seen to 
lie on an arc-like line of weakness. Both this series and that of 
Horbiger are seen to diminish in size to the east. This decrease in 
diameter seems to represent a decrease in available energy-with- 
time as the eruptive phase passed. 

On a somewhat larger scale it is noticeable that most of the 
lunar features can be found to be aligned along a number of inter- 
secting imaginary lines. Around Mare Imbrium a radial alignment 
is evident, whilst the large groups of craters such as Arzachel- 
Alphonsus-Ptolemaeus and Cyrillus-Theophilus-Catharina, are 
seen to be aligned along great circles running north-south. 
Furthermore, on close examination many of the large craters are 

1 On some maps this formation is called 'Hellplain'. 



seen to possess a distinctly polygonal outline. This phenomenon 
and the others mentioned above can be almost certainly put down 
to stresses to which the lunar crust was subjected. (There is an 
analogy here with the famous columnal basalts of the Giant's 
Causeway in Antrim, where hexagonal columns of rock, due to the 
cooling of a formerly homogenous rock mass around centres, are 
exposed.) If, as some scientists believe, the Moon was at some time 
in its history 'captured' by the Earth, then there would be one 
explanation for the setting up of stresses in the lunar crust. Another 
cause of such forces could be the gradual cooling of the Moon and 



Fig. 1 . Crater series along south-east flank of Horbiger 


the release of stress in the form of volcanic activity. This in turn 
could lead to gradual devolatilization of the core and the diminish- 
ing intensity of eruption as is exhibited in the lunar features. How- 
ever, this point is one that is wide open for discussion at the present 

The great dark maria, so prominent as vast plains on the face of 
the full Moon, contrast vividly with the bright-walled craters that 
have been discussed. Some, such as the Mare Crisium, are fairly 
regular in outline, whilst others, such as the Oceanus Procellarum, 
are less clearly defined and are much larger. Indeed, the smaller 
maria seem to grade down into the largest of the walled plains. 
This may point to a similar origin, although a difference in scale is 
implied. On the surfaces of the various 'seas' are found craters, 
peaks, wrinkle ridges, valleys, crater rows, domelike swellings, 
faults and numerous other smaller structures. The sinuous winding 
ridges - 'wrinkle' ridges - are found to represent the former boun- 
daries of old walled plains which have subsequently been inun- 
dated by lavas or collapsed with the formation of younger calderas. 
Large craters such as Archimedes (on the Mare Imbrium) and 
Copernicus (on the Mare Nubium) are typical, and obviously of 
later date than the maria on which they stand. The borders of these 
vast areas are in some places defined by high mountainous ridges, 
such as the Apennines, the Percy Mountains and the Alps, and in 
others only by a change from dark 'lunabase' material to the 
brighter 'lunarite' material which is so typical of the crater-strewn 

Less prominent yet exceedingly interesting are the low, roughly 
circular swellings or 'domes' which after careful search can be seen 
to lie scattered about the mare floors. From their distribution it 
would seem that the mare borders are the most favoured places 
for them. A fine group is found between Hortensius and Tobias 
Mayer, east of the large terraced crater Copernicus ; another lies in 
the vicinity of Diophantus and De LTsle. Most of the swellings 
have at their summit small pits which would seem to have been 
formed by the feeble rising of magmatic gases characteristic of the 
final stages of an eruptive phase. The domes probably find an 


analogy in the endogenous lava domes seen in the volcanic regions 
of the Earth. The apophyses sometimes found growing from the 
lunar features are also in accord with this view. 

Numerous chain-like systems of craters exist. Generally they 
can be explained as having followed migrating magmatic activity 
along crustal weaknesses. Fissure eruptions of this calibre can be 
seen in Iceland (Threngslaborgir, for example). In many cases the 
walls of the separate components of the chain have been destroyed 
by later eruption in the form of the adjacent crater and partly 
washed down by the action of hot lava streams. As was noticed to 
be the case with valleys and craters, so a rough alignment of crater 
chains is traceable along a system of grid-like directions. The dia- 
gram (Fig. 2) shows a number of such crater rows (also known as 
crater valleys) near the Moon's western limb. Clearly in this case 
one series of craters has found a line of weakness corresponding to 
the rim of the plain Hagecius and another to the east side of 
Pontecoulant South. (To gain some idea of the scale, the well- 
formed crater 'K' adjacent to Pontecoulant is 20 miles across.) 

Other linear valley features are not quite so easy to explain. 
Structurally they are long linear depressed areas and very narrow 
in comparison with their length. Crateriform bulges are not 
present and so it would seem that they do not represent the 
ultimate form of washed-down crater chains as described above. 
It rather appears, then, that they are rifts in the lunar crust which 
have been brought about by the stretching of the crustal layers as 
the Moon cooled. This does not mean to say that they are bottom- 
less cracks; far from this; they have definite floors which are 
generally convex. Possibly they represent the lunar equivalents of 
the Earth-type 'graben'. They are undoubtedly guided by fault 
planes, but to what extent hot magmas rose along these planes, 
melting the crust underlying the rifts and incorporating blocks of 
country rock, it cannot be said with any certainty. 

Having described most of the features found on and about the 
maria, it remains to provide a possible explanation for the occur- 
rence of the maria themselves. From their very nature it appears 
that lava has washed their floors and faulting has played a large 



Fig. 2. Crater rows and valleys near the Moon's western limb 

part in determining their boundaries. The present writer, there- 
fore, believes them to be the ultimate form of subsidence feature 
on the Moon. The fact that few maria exist on the other side of the 
disk (viz: Russian Lunik photos) seems to indicate that the exces- 
sive stresses set up on the side facing the Earth (the Moon has a 
captured rotation), allowed imprisoned forces built up beneath the 
lunar crust to escape at a late stage in the form of tectonic activity. 


Yet again this is a highly controversial point, and the reader should 
study other views before reaching his own opinion. 

One last major problem remains to be discussed - that of the 
lunar 'rays'. Anyone who has seen the full Moon through a tele- 
scope will have noticed the long bright streaks radiating from such 
craters as Tycho, Copernicus and Kepler. When closely studied 
under high magnification, fine structure is revealed, and the rays 
are seen to consist of thousands of separate streaky patches all 
lying in the general direction of the whole system. Some of these 
stop against crater walls and mountain blocks, and this indicates 
that they are explosion features. The fact that a ray-free halo lies 
around each crater forming the centre of a ray system adds weight 
to this idea. Rays are recent lunar features, since they cross the 
smaller craters, and thus it is likely that they are the youngest 
features. Whether they are masses of volcanic dust sent out from 
their parent craters, or finely comminuted lava droplets, remains 
for the first space-men to find out. The Moon will hold many 
problems for lunar 'geologists'. 

The Great Red Spot on Jupiter 

W. E. FOX 

The year 1964 will find Jupiter in a more northerly declination 
than for some years past, rendering it a favourable object for 
observation by observers living in the northern hemisphere. 

When first seen in an astronomical telescope the planet is indeed 
an impressive object, its belts and zones never failing to impart a 
sense of wonder and delight to the thinking person with a desire to 
learn more about the universe in which we find ourselves. A 3-inch 
diameter telescope will, in good seeing conditions, reveal much on 
the surface of the planet, but a larger aperture is preferable if one 
wishes to study it in greater detail. It will be found that many 
spots, both dark and light, are in existence on the surface, and it 
has been the policy of the B.A.A. Jupiter Section, for many years 
now, to examine and study the motions of these features. By doing 
so, various drifts in longitude and changes in the appearance of the 
belts and zones have been detected giving rise to the differential 
rotation periods existing in the visible upper layers of the planet's 

While many of these markings have their own particular 
interest, none has attracted so much attention as the Great Red 
Spot. It lies in the latitude occupied by the South Tropical zone 
and the south component of the South Equatorial belt, but over 
the years its longitude has been subjected to considerable change. 
In appearance it takes the form of a large ellipse, upwards of 
26,000 miles along its major axis and some 12,000 miles across its 
minor axis, often with a strong red colour varying in intensity to 
pink and neutral grey, sometimes disappearing completely, though 
at such times its position is revealed by a large bay in the south 


edge of the South Equatorial belt now known as the Great Red 
Spot Hollow. 

The long-enduring character of the feature has been established 
beyond all possible doubt, but it was in the year 1878 that the 
attention of observers was especially directed to the Red Spot, for 
it was then that it assumed a prominence hitherto not recorded. 
From 1879 to 1882 it dominated the surface of the planet not only 
by reason of its great size but also because of its striking red colour 
- hence its name. It became so prominent that it could easily be 
seen in telescopes of less than 3 inches of aperture. There is no 
doubt, however, that it had been a well-observed feature long 
before 1878, for that keen-eyed observer the Rev. W. R. Dawes 
figured it on his drawings in November 1857, while a few years 
later it was independently recognized by other observers including 
Jacob, Baxendell, Huggins and Long. 

W. F. Denning, from records of longitude determinations, 
computed rotation periods for the Red Spot over a number of 
consecutive intervals between the years 1831 and 1878 which show 
a close relationship to those found in more recent times. It is on 
record that Hooke, Cassini and others with their inferior instru- 
ments, observed a spot in 1664 and later years, which appeared in 
the same latitudes and had nearly the same rotation period, and to 
these men, in particular Hooke, must go the credit for the dis- 
covery of what has proved to be one of the most remarkable 
planetary markings ever seen. 

If this identification is correct, then the Great Red Spot is at 
least 300 years old, which is, as B. M. Peek remarks, 'a truly 
venerable age for a feature that is manifested only in the planet's 
atmosphere'. According to the records of the rotation periods 
computed by Denning, we find a mean value of 9 hrs 55 min 32 sec 
in 1831-2, which gradually lengthened until the years 1856-60, 
when it had reached 9 hrs 55 min 38 sec, after which the period 
shortened to 9 hrs 55 min 33 sec in 1876-78, but by 1885-86 this 
had lengthened to 9 hrs 55 min 41 sec, at which the Red Spot, with 
small variations, remained reasonably steady until the year 1909. 

Some of the early observers put forward the suggestion that 


they were observing a volcano erupting on the solid surface of the 
planet causing a red glow in the clouds above the seat of the erup- 
tion, but a study of the rotation periods reveals that, far from being 
related to some landmark on the solid nucleus, the Red Spot had a 
motion of its own, moving backwards and forwards in longitude, 
and, in fact, between the years 1831 and 1885, when its rate of 
rotation had been less than 9 hrs 55 min 40 sec, it was actually 
drifting round the planet in the direction of rotation. In 1872-73, 
when the period of the Red Spot reached the time of 9 hrs 56 min 
31 sec, the rate of drift was actually —7° per month. From 1885 
onwards to 1909 the rate of drift varied from 0° to +l°-5 in the 
direction opposite to the planet's rotation. An object with such a 
wandering tendency must surely be floating in the upper layers of 
the planet's atmosphere. One writer has referred to the Red Spot 
as a floating island moving more slowly as it breaks through the 
clouds to higher levels, lagging behind, as it were, as the planet 
rotates on its axis, a fact fully confirmed by observations over 
many years. 

During the apparitions of 1900 and 1901 a remarkable feature 
developed, destined, as it proved in later years, to have a profound 
influence on the motion of the Red Spot. A series of dark humps 
could be seen projecting from the south edge of the South 
Equatorial belt, one of which became very prominent early in 1901 . 
On February 28 of that year P. B. Molesworth recorded that this 
spot had become connected by a greyish filament stretching across 
the South Tropical zone with a dark streak on the South Tem- 
perate belt. This filament became rapidly distended in longitude, 
and brilliant white spots developed at its preceding and following 
ends, the portion between the white spots becoming somewhat 
darkly shaded. It was to this shaded portion that the name 'South 
Tropical Disturbance' was given, and it was found that the whole 
of this disturbance had developed a rotation period of 9 hrs 55 min 
20 sec. It was at least 90° from the longitude of the Red Spot, 
which had at that time a rotation period of 9 hrs 55 min 41 sec. It 
was clear to the observers of that day, that the new feature if 
sufficiently long lived, by reason of its more rapid motion, would 


certainly overtake the Red Spot in due course. This indeed hap- 
pened in June 1902, when the preceding end reached the following 
end of the Red Spot. 

Interest was centred upon the manner in which the two objects, 
existing in the same latitudes, would react upon each other. What 
actually occurred was quite unexpected. Instead of obliterating the 
Red Spot and the Hollow in the south edge of the South Equatorial 
belt, the whole of the latter became surrounded by the dusky 
shading of the Disturbance, the preceding end of which could be 
seen re-forming at the preceding end of the Red Spot. Within 
three months the South Tropical Disturbance, the whole of which 
totalled a length of 90° of longitude, had passed round the Red 
Spot. This was the first observed conjunction of the two features. 

The second and third conjunctions occurred in 1904 and 1906, 
by which time the South Tropical Disturbance had shrunk in 
length somewhat, and its passage from end to end of the Red Spot 
and Hollow was accomplished in about 14 and 12 days respec- 
tively, though it must be admitted that some of the observations 
are somewhat uncertain. The fourth, fifth and sixth conjunctions 
took place in 1908, 1910 and 1913-14, and the observations estab- 
lish the fact that the material composing the South Tropical Dis- 
turbance was again transferred rather rapidly from the following 
to the preceding ends of the Red Spot, but this phenomena was 
much protracted at the seventh conjunction which continued from 
1917 to early 1920. At this time the Disturbance had increased its 
length considerably, reaching a maximum of more than 190° of 
longitude. The conjunctions described had the effect of shortening 
the rotation period of the Red Spot until 1924, when it reached the 
shortest recorded in the twentieth century of 9 hrs 55 min 32 sec. 

Describing the eighth conjunction, which became only partial, 
the Rev. T. E. R. Phillips (then Director of the B.A.A. Jupiter 
Section) wrote 'The motion of the Red Spot had become so 
accelerated that it was actually receding from the preceding end of 
the Disturbance and its rotation period was definitely less than 
that feature', a state of affairs which continued during the appari- 
tion of 1925. From 1926 to 1928 the Disturbance became invisible 


and when seen again in 1929 was found to have extended to some 
220° of longitude, while the rotation period of the Red Spot had 
resumed its more usual rate; at the same time the motion of the 
preceding end of the Disturbance became accelerated. 

The ninth conjunction began in 1928, by which time the Dis- 
turbance had reached a length of 240°, but its effect on the motion 
of the Red Spot was now considerably reduced, the two features 
remaining in conjunction until 1935, when the Disturbance again 
became invisible, all trace of it being finally lost in 1939-40. From 
1909 to 1939 the Red Spot had actually drifted two and a half 
times round the planet in the direction of rotation, but after the 
disappearance of the South Tropical Disturbance it began to drift 
against the rotation, having now, in 1962, reached a point in 
longitude some 300° from where the backward drift began - more 
than three-quarters the distance round the planet. 

We naturally ask ourselves 'Was the rapid motion of the Red 
Spot in the middle of the nineteenth century due to a similar South 
Tropical Disturbance having a similar influence to that so well 
recorded during the first part of the twentieth century, and is it 
part of a periodic phenomenon not yet fully understood ?' If so, 
surely future generations of observers will again witness these 
events. Long-period schemes of observation over many decades 
may be necessary to supply the solution to the problem. 

That the South Tropical Disturbance is likely to be renewed 
was suggested by the events which began in 1955. B. M. Peek, a 
former Director of the Jupiter Section, observing in the early 
morning of 1955 September 19 with a 3-inch telescope, observed a 
filament across the South Tropical zone which reminded him 
strongly of Molesworth's observation of 1901. The feature grew in 
length and at maximum extended over 42° of longitude, and after 
some variations exhibited a rotation period not unlike that of the 
old Disturbance. The new feature was observed with much interest 
and it was conjectured that the earlier events might be repeated; in 
fact, it appeared that the stage was set in readiness for this to 
happen, but the new Disturbance was short-lived and it dis- 
appeared in 1957, having never reached conjunction with 


the Red Spot, which, of course, showed no sign of being 

Other phenomena which have a profound effect on the Red 
Spot are the outbreaks of activity on the South Equatorial belt 
which occur from time to time. These are too numerous and com- 
plicated to describe in detail, but a brief summary of the events 
will suffice to record the appearance of these eruptions. The south 
component of the belt is often so faint as to be almost invisible, a 
state of affairs which may continue for an indefinite period. A 
revival begins by the outbreak of a small spot between the com- 
ponents from which other spots begin to move in opposite direc- 
tions, those on the south edge moving in increasing longitude, 
while those on the north edge move in decreasing longitude. After 
a period of some weeks the two streams begin to pass each other 
on the opposite side of the planet on which the eruption began. On 
reaching the vicinity of the Red Spot, the spots on the south are 
usually deflected northwards round it, eventually forming the well- 
known Hollow in this portion of the belt. A scene of great turb- 
ulence develops and eventually the Red Spot begins to fade, losing 
its characteristic appearance. It is then that it appears to sink 
below the upper cloud layer and often entirely disappears, being 
replaced by a pale oval bounded on its north side by the Hollow. It 
is only when the great activity on the South Equatorial belt is sub- 
siding that the Red Spot makes its reappearance. 

Photography has been brought into use for recording the 
various Jovian features. As far back as 1927, W. H. Wright of the 
Lick observatory made a real contribution to our knowledge of the 
planet by a series of images obtained in light of different wave- 
lengths from ultra-violet through the spectrum down to infra-red. 
There is a distinct reduction in the size of the disk of the planet as 
the prints reach the longer wavelengths with their deeper penetra- 
tion of the atmosphere, while on the shorter wavelengths from 
ultra-violet to blue the Red Spot shows strongly in the upper layers. 
The method has been followed in more recent years by others, 
particularly J. H. Botham of Johannesburg, whose ultra-violet 
photographs in 1960 show the Red Spot very strongly, while 


exposures in infra-red light taken within a few minutes of the ultra- 
violet ones show absolutely nothing of the Red Spot, surely a 
reliable method of recording the atmospheric levels of various 

During the early months of 1955 Dr. B. F. Burke and Dr. F. L. 
Franklin of the Carnegie Institute of Washington were engaged 
upon making a radio survey of certain portions of the sky known 
to contain radio sources. One of these was the well-known Crab 
Nebula and some other feebler sources. In addition to these 
'noises', they obtained some signals from a hitherto unknown 
source whose strength at times greatly exceeded anything they had 
received previously. They eventually traced the signals to the 
position occupied by Jupiter, which was in that part of the sky at 
the time. Having located the source of this new radio emission, 
astronomers were curious to find out whether any special localities 
on the planet were responsible. This proved a difficult problem, 
but Dr. C. A. Shain of the Commonwealth Scientific and Indus- 
trial Research Organization at Sydney, N.S.W., who carried out 
much research in the matter, suggested that the larger number of 
'noise' bursts followed a rotation period close to that of some 
white ovals on Jupiter's South Temperate zone, with some evidence 
that at times the reception of signals is very strong when one of the 
white areas is in conjunction with the Red Spot. It is not known 
whether the Red Spot itself is an independent emitter of radio 
waves, but later investigations still show a strong tendency for 
emissions to occur when it is crossing the disk of the planet. 

There is much research to be done, and observers, each in their 
own particular field of work, be it visual, photographic or radio 
research, may eventually throw some light on what is probably one 
of the most remarkable and interesting planetary objects - the 
Great Red Spot on Jupiter. 

Telescope Mountings 


Telescope mountings fall into two classes : altazimuth and equa- 
torial. The altazimuth is the type of mounting that one usually 
finds with telescopes set up on seaside promenades or piers, where 
they serve admirably, as the telescope is required to swing up and 
down or from side to side as the viewer switches from the passing 
battleship to the girl on the beach. 

Celestial objects, however, show slow rotation round a point in 
the northern hemisphere of the sky close to the Pole Star, so that 
they traverse great arcs at the celestial equator. To follow a star or 
planet therefore means that one has to keep moving the telescope 
from east to west, and at the same time raise its altitude if the star 
is rising in the east or lower the altitude if the star is on the western 
side of its southing point. As these two movements have to be 
made simultaneously, they are not easily carried out with smooth- 
ness ; there is the added difficulty that an astronomical telescope 
gives an inverted image, and the beginner may be somewhat con- 
fused by finding that the instrument has to be moved in the direc- 
tion opposite to that which is expected. When an object is low in 
the field, for instance, it has to be brought to the centre by raising 
the angle of the telescope instead of dropping it. 

With even slight experience, it is surprising how quickly one 
becomes used to these motions, and the altazimuth mounting 
should not be discarded out of hand, even though it has obvious 

For cheap refractors, the usual and worst type of altazimuth 
mounting is the compass joint. This tends to be jerky in operation, 
and is very often coupled with the pillar and clawtable stand, which 
is a highly undesirable feature. Such telescopes are presumably 


intended to be used on a table at a window. No serious observer 
would even consider doing anything of the sort - and tables small 
enough to be carried outdoors are never rigid enough to be satis- 
factory, as well as being inconveniently low. 

Better refractors usually adopt the tripod stand, together with 
what is termed a trunnion mount - in which the telescope is sup- 
ported between two extended arms which rotate upon the tripod. 
In the more elaborate models, this rotation is controlled by a 
worm and wheel hand-control, while a steadying rod leads off 
from the tripod to the eye-end of the telescope, thereby adding 
stability and also providing another form of hand-control slow 
motion. Slow motions are essential when using high powers, since 
it must be remembered that the slightest tremor will be magnified 
several hundred times when the instrument is being used. 

The trunnion mounting can be quite well adapted to reflectors ; 
my own 12J-inch was thus mounted. A good point, too, is that the 
eyepiece always remains in a comfortable and accessible position. 
I found that I could make variable star observations much more 
speedily than when using an equatorially-mounted telescope, and 
it was not at all difficult to follow the planets when making draw- 
ings of them. 

For a small Newtonian reflector - a 6-inch, say - the mounting 
can be almost identical with that of the refractor, but the tripod 
need only be short, since the eyepiece is at the top end of the tube. 
This is, indeed, one of the most convenient features of a Newton- 
ian reflector, since it makes for comfortable viewing; it is easy to 
turn the telescope to the zenith or overhead position, whereas with 
a refractor the observer may well have to lie almost flat (unless, of 
course, the tripod is extremely high). Some owners of refractors 
make use of star diagonals, but these cause loss of light as well as 
producing confusing reversals in the orientation of the image. 

My 12£-inch reflector had a permanent mount. The column 
consisted of a tube of sheet iron, riveted up, though an old oil- 
drum would have served just as well if I had had one available. I 
hunted round a car-breaker's yard, and found an old lorry flywheel 
with a toothed edge and a small-diameter starter cog to engage 


with the teeth; I also managed to find three ordinary ball-races of 
about 2 inches diameter. (The total expenditure was only a few 
shillings.) A hole was dug, and filled with concrete, with a few 
short pieces of iron rod pushed in to the centre. The roll of sheet- 
iron to form the column was put over these rods, and was then 
filled to the top with a mixture of three parts sand to one of cement, 
with rather more water than one would generally use. The flywheel 
with its short length of shafting was then pushed down into this 
soft mixture, and, after careful levelling, was allowed to set for 
several days ; eventually it became as firm as a rock. A short piece 
of straight shafting on the upper side of the flywheel was used as 
the central pivot, and the weight of the two oak beams supporting 
the telescope was taken up by the three ball-races, which were 
bolted on to an iron ring attached to the stout cross-member under 
the beams. The beams were left rather long on the side opposite to 
the telescope, in order to reduce the amount of counterweight 
required. It should always be remembered that it is important to 
make the mounting, as well as the telescope, so that it is in a state 
of balance without having to rely upon undue friction. 

The second basic type of mounting, the equatorial, makes use 
of an axis of rotation inclined toward the celestial pole (the point 
around which the sky appears to revolve ; the inclination is of course 
equal to the observer's latitude). It is easy to see that with an 
equatorial, the telescope will keep any selected object in view with 
one movement only. A clock drive may be attached to the polar 
axis, so that the telescope moves at a rate just sufficient to compen- 
sate for the diurnal motion of the sky and keeps the object in view. 
A refinement is to fit a circle on to the axis, divided into 24 hour- 
divisions - the right ascension circle - while the other movement, 
the altitude, can be checked by a similar circle, marked in degrees 
and known as the declination circle. 

Circles are very useful if the telescope is permanently set up; 
they may be helpful in finding Venus in the daytime, for instance, 
and are invaluable for locating faint objects which are not readily 
visible. Yet they are of little use for portable telescopes, and my 
personal view is that they are sometimes used more than is strictly 


necessary. It is far better to find a faint object by using a good star 
atlas rather than to rely wholly upon setting circles. 

There are various types of equatorial mountings, though all are, 
of course, based upon the same principle. The most common, 
probably, is the German. This has the usual inclined axis ; from a 
T-shaped bearing another shaft extends at a right angle, one side of 
which takes the telescope, while the other side is fitted with a 
counterweight to maintain balance. Nearly all refractors are 
mounted in this way, and most amateur telescope-makers auto- 
matically adopt it when setting out to make an equatorial mount. 
Yet while the German works well with refractors, it is by no means 
so satisfactory with reflectors, as it requires precision engineering, 
coupled with a very large declination axle. Many amateurs make 
this bearing far too thin, with a considerable degree of overhang. 
It is claimed that in such a case, the shaft is still quite strong 
enough to take many times the weight that it actually has to carry. 
This may be true; but strength should never be confused with 
stability - and it is stability which matters most. Nothing is more 
frustrating than to try to observe details on, say, Mars or Jupiter, 
when the telescope is quivering in the breeze. Stability may be 
obtained by giving large bearing surfaces and a high degree of 
inertia, together with plenty of weight. In fact, the heavier a 
mounting, the better it is likely to be. 

Next let us consider some mountings which are not suitable for 
refractors, but which may be recommended for reflectors of all 
sizes. First there is the English type - familiar to all astronomers, 
since it is used for the 100-inch reflector at Mount Wilson. Here, 
the telescope is pivoted inside a large yoke, inclined at the correct 
angle of latitude, and supported by a pier. This mounting is 
extremely suitable for amateur telescopes, as it requires no preci- 
sion engineering whatsoever. The tall pier should have a base 
going well down into the ground; it must extend below the frost 
line, and must have sufficient 'roots', as otherwise it will tend to 
shift when leaned against by a well-meaning friend. (This is no 
exaggeration; I have known it happen). A small concrete stump is 
needed to support the yoke at the other end, and this, along with 


the tall pier, should have a halved Plummer block bolted on to the 
top, so forming the bearings for the short axle stubs which extend 
from each end of the yoke. 

The yoke itself may be made of wood, provided that it is sub- 
stantial enough. For a 12-inch reflector I have known wooden 
railway sleepers to serve excellently. Slotted angle-iron is another 
suitable material. However, in my view the best material is a cast- 
ing made of three parts sand to one of cement mixture; reinforcing 
iron does not really add much to the strength, and may well have 
the effect of breaking up the material in which it is embedded. 
Always provided that the mounting made in this way is massive 
enough, it will have plenty of strength. Concrete does not vibrate 
so readily as metal, and for this reason is to be preferred. To form 
the yoke, a rough wood and fibre-board mould can be constructed ; 
a piece of wood or a metal mandrel which has been wrapped round 
with several turns of wax paper is inserted at each end, and when 
the mandrels are removed from the hardened concrete they will 
form the holes for the axles of the yoke. Two similar holes are 
made in the centre of each side, to take the bearings of the telescope 

If one selects the right time of year to carry out the operation, 
there is no reason why the casting should not be carried out in the 
ground instead of in a specially-prepared mould. This involves 
levelling off a patch, and carefully digging out the required shape 
with a spade and trowel, setting in the mandrels and then filling in 
to ground-level with the concrete mixture. After a sufficient period 
of time (probably at least a week) the surrounding earth may be 
dug away, but the casting should be left for a few days before being 
finally taken up from the ground, as it may easily crack if it is still 
in the so-called 'green' condition. If it should break, there is, 
unfortunately, nothing to be done except smash it up and use it to 
make a rockery. The materials themselves are extremely inexpen- 
sive, but a failure means an annoying waste of time, and it is 
obviously unwise to try to hurry the operation. 

If it becomes necessary to drill small holes in any of the concrete 
components, the best instrument is a twist drill with a tungsten 


carbide tip, easily obtainable from any good tool-shop or builder's 
merchant. The hole is then plugged with any of the patented 
materials sold for this purpose, and the screw inserted in the usual 
way. Any holes can naturally be 'touched up' with a trowel and a 
little cement mixture. 

After a much longer time, perhaps as much as a year, the cast- 
ing may be given several coats of paint to improve its appearance. 
The reason for delay is that cement is alkaline, and unless it is 
weathered out completely it will cause rapid deterioration of any 
paint applied to it. 

Next let us consider the fork mounting, which is not unlike the 
yoke, but has the yoke cut in half so that there is now no upper 
portion or tall pier. This means that the bottom axle must be 
lengthened and made considerably stouter, since it is now sup- 
ported only at the base. The telescope tube is pivoted between the 
prongs of the fork. The mount should be made so that the mirror 
end is able to pass right through the arms. If so, the telescope can 
reach the area of the celestial pole, which is an unavoidable 'blind 
spot' with an English equatorial. 

With a fork mounting, the difficulty is to make the lower bear- 
ing to the right length and proportion. This is avoided with the 
last type of mounting to be considered here: the Foucault. With 
the Foucault, the polar axis is supported at its end by a single ball 
or thrust race, and broadens out into a large disk with a machined 
edge which is supported by two ball-races. Two stout arms are 
bolted on to the face of the flat disk, forming the arms between 
which the telescope is mounted. In my personal view, the Foucault 
is the best possible type of mounting for a reflector. It is low and 
compact; the points of balance do not overhang; and if the arms 
are stout, there should be no troublesome vibrations. 

To construct a Foucault, the first essential is to obtain a large 
flywheel, complete if possible with a short length of shaft. The 
flywheel should have at least twice the diameter of the telescope 
mirror. Flywheels of such a type are used for driving machinery by 
means of belts, and the edge will be quite smooth unless the wheel 
has been badly exposed to the weather. The arms can probably be 


bought complete as a couple of extended plumber brackets, and 
may be either bolted or screwed on to the flywheel; alternatively, 
they can be prefabricated. The base of the mounting is a triangle, 
made up from ordinary angle-iron, and welded; it may, of course, 
be constructed from slotted metal fixed together by nuts and bolts, 
with projections extending from it to take the ball-races which 
support the main weight. 

To make a clock drive for a Foucault-mounted telescope 
involves using a large toothed bronze wheel, which should be 
fitted on to the shaft a short way down from the flywheel, the teeth 
engaging with a single start worm in stainless steel if possible. Do 
not make the mistake of having the teeth too fine in the hope of 
getting a better drive. It is much better to have deep-set, rather 
coarse teeth, so long as the worm is a really good match. There is 
no need to allow for throwing the worm in and out of engagement, 
provided that teeth of this type are used. If everything is well- 
balanced, the toothed disk need be only in slight frictional connex- 
ion with the shaft to impart the drive to the telescope, and at the 
same time allow the instrument to be swung around to different 
objects without any noticeable drag or strain. This is not so when 
fine teeth are used, since any attempt to move the instrument will 
tear the teeth hopelessly unless they are completely disengaged. 
This, again, is no exaggeration; I have seen teeth so fine that they 
could be compared with those of a nail-file ! 

A small electric motor, such as that used in a gramophone, 
serves quite well for the actual drive, since the required power is 
extremely small owing to the tremendous gearing-down. Gear- 
boxes are obtainable to effect the major part of this reduction, but 
I have seen efficient drives which have been made entirely from 
Meccano gears and worms mounted on short spindles between 
metal plates. 

Finally, it is important to remember that no matter what type 
the mounting may be, or how well it is constructed, it is always 
difficult to prevent a long tube from being shaken in gusty weather, 
and so it is wise to consider the tube at the same time as the 
mounting. By making a skeleton instead of a solid tube, the effects 


of wind-resistance may be largely overcome. It is also prudent to 
make the telescope of fairly short focal length, say/5 to/6; if 
higher magnifications are needed, they may be obtained by using a 
Barlow lens, which in any case gives better results than very short- 
focus eyepieces. 

All in all, the making of a telescope mount is just as important 
as the making of the telescope itself. If the mounting is unsteady, 
or defective in any other way, the instrument will never be able to 
be used to its full capacity - and this vital point is all too often 

Astronomy and Navigation 


To many of those who have not been caught by its fascination, 
astronomy appears to be a highly theoretical science, which pur- 
ports to tell us a great deal about the outer reaches of space, but 
can tell us next to nothing about the Earth a few miles under our 
feet. This attitude is hardly softened when astronomers, on 
theoretical grounds, double the already unimaginable distances 
overnight. And yet, from the very earliest times, the study of 
heavenly bodies has led to severely practical results. 

We do not know when man first took to the water and fashioned 
boats which, from mere floating logs, developed into craft capable 
of voyaging long distances out of sight of land. It is, however, 
certain that it was very long ago indeed that the discovery was 
made that Sun and stars could be used to point the navigator's 
way over the trackless waters. It is believed that bees certainly, and 
migrating birds almost certainly, use the Sun for navigational 
purposes. Primitive man, we may be sure, had the same ability to 
some degree. 

It was in about 200 B.C. that Eratosthenes used the basic prin- 
ciple of astro-navigation to measure the size of the Earth. He knew 
that at the summer solstice the Sun was vertical at midday at the 
town of Syene, and that Alexandria was nearly due north of Syene. 
He also knew the distance between the two towns. By measuring, 
with the aid of a shadow cast by a pillar, the distance of the Sun 
from the zenith at noon on the day of the summer solstice at 
Alexandria, he was able to estimate the circumference of the 
Earth. What is more, his estimate is believed to have been a very 
good one - much better than the approximation which made 
Columbus mistake the West for the East Indies. 


Eratosthenes' method was about as simple as anything could 
be. Since the rays of the Sun can be taken as parallel, it is obvious 
that the angle by which the Sun was lower than the zenith at 
Alexandria must be the same as the angle at the centre of the Earth 
subtended by the two towns. He made this angle 7J° and the dis- 
tance between Alexandria and Syene 5,000 stadia. It follows that 
5,000 stadia is to the circumference of the Earth as 7£° is to 360°, 
the Earth, therefore, would be 240,000 stadia in circumference. 

Astro-navigation is founded upon this simple principle. Yachts- 
men and others who have attempted to master the subject have 
sometimes been given the impression that navigation is a highly 
abstruse and difficult art. In principle, nothing could be further 
from the truth. The complexity and the difficulty of working an 
actual sight only arise because of the many allowances which have 
to be made for variable factors and the need for exact calculation 
by spherical trigonometry. 

Anyone possessed of a good-sized globe and a pair of dividers 
could work out a position in a few moments, to a degree of 
accuracy which would not be good enough for bringing a ship into 
port, but which would have seemed a miracle to Columbus. During 
the war, I fixed the position of a convoy to within about fifteen or 
twenty miles with nothing to aid me but observations of the times 
of sunrise and sunset. The tools employed were the naked eye, a 
child's school atlas, Whitaker's Almanack and a wrist-watch 
checked by the B.B.C. pips on the radio. The last was the one 
advantage I possessed over the early navigators. Latitude is child's 
play ; but for longitude accurate time is needed. 

If we look back at Eratosthenes' experiment, we shall see that 
there were three measurements involved and that, if we know any 
two, we can at once deduce the third. Given the circumference of 
the Earth and the zenith distance of the Sun, one can at once 
calculate the distance between Alexandria and Syene. 

For us, the matter is even simpler than this. We measure dis- 
tances due north and south not only in miles but sometimes in 
degrees of latitude. It is apparent from the drawing that 1\° is the 
difference in latitude between Alexandria and Syene. But, since 



""» v Sun s zenith /£ 
o \ distance i 

Sun's elevation 
at Alexandria 





^5000 StaaV^~ 

we know that at the summer solstice the Sun is 23 J° north of the 
equator, the latitude of Alexandria, using Eratosthenes' figures, 
must be 23 \° + 1\°, or 31°N. - which is almost exactly right. 

There is, however, nothing unique about the position of the Sun 
at the summer solstice. We can, by looking at the Nautical 
Almanac, find the declination of the Sun north or south at any 
time on any day of the year. If we want to find out latitude, all we 
have to do is to measure the elevation, and hence the zenith dis- 
tance, of the Sun when it is at its maximum, and this tells us how 
many degrees we are north or south of the place where the Sun is 
at the zenith at that instant. By adding or subtracting the declina- 
tion of the Sun, as the case may require, we can at once find our 

The only qualification to this is a comparatively trivial one. If 


we are very far east or west of Greenwich, and do not know the 
correct time, we may be slightly out in our reading of the Sun's 
declination. Using a rough approximation, however, the error will 
be slight. 

The Sun is not the only star which we can use in this way. 
Indeed, other stars are more convenient, because their declinations 
do not alter from day to day. If the Pole Star were exactly at the 
celestial pole, all we should have to do would be to measure its 
elevation, and that would be our latitude. In exactly the same way 
as we used the Sun, we can take any star, measure its zenith dis- 
tance when it is in transit, add or subtract its declination, as is 
appropriate, and that is our latitude. 

This was the method used by the early explorers. By the use of 
the astrolabe, a primitive form of sextant, they could determine 
latitude from the Sun or a convenient star. The latitude of the 
destination would be known, and all that was required was to 
steer well to the west or east of the destination until its latitude was 
reached, and then turn and sail along that latitude. One was bound 
to arrive at the right place in due course. 

Given access to the correct time, longitude is nearly as easy to 
find as latitude. A moment's reflection will make the point clear. 
In order to find the moment of transit of a star, including the Sun, 
it is not necessary to know the time. All that one has to do is to 
take a series of elevation measurements until the reading is a 
maximum, which occurs at the moment of transit. 

In obtaining a fix in both latitude and longitude, the Sun, or any 
convenient star, is observed when it is not at its maximum eleva- 
tion. In these circumstances, nothing can be known about the 
exact point on the globe where the star in question is at the zenith 
point without also knowing the exact time. We can calculate our 
distance from the zenith point just as easily; but this is singularly 
little use unless we know where the zenith point is. The case of a 
latitude reading is merely a special case, because we know that the 
Sun, or other star, is due south of us, as well as knowing its 
declination, and therefore know its exact zenith point without 
knowing the time. 


Let us turn back to the drawing of Eratosthenes' experiment 
and generalize it. We can leave out all directions and still deduce 
much the same facts. For every degree we are removed from the 
Sun's zenith point, in any direction, the Sun will appear one degree 
from the zenith. This is really all that the drawing is showing us. 
If we substitute for the word 'Syene' 'Zenith point of the Sun' and 
for 'Alexandria' 'position from which zenith distance of the Sun is 
measured' and leave out the '5,000 stadia', the drawing is equally 
valid, though more general. 

As I have said, the Sun is not the only star which can be used in 
this way. It-is convenient because its height above the horizon can 
easily be measured, whereas other stars are apt to be visible at a 
time when the horizon itself is invisible. At dusk and dawn, how- 
ever, bright stars can be used. 

A star other than the Sun circles over the latitude which is given 
by its declination. A knowledge of the time will tell one over what 
point of longitude it is at zenith at any given moment, and this 
point can be marked on a map, chart or globe. The same is true of 
the Sun, except that the latitude must be corrected for its changes 
in declination. These positions are given in nautical almanacs and 
can easily be looked up. 

Having measured the elevation, and deduced the zenith distance 
by subtracting from 90°, and marked the position at which, at that 
instant, the star being used is at zenith, the next step is obvious. 
The zenith distance tells us how many degrees we are away from 
the zenith point. If we are using a globe for rough navigation, we 
can then set a pair of dividers to that number of degrees, as 
measured between latitude circles. If we then trace with the dividers 
a circle, with the centre at the zenith point, we know that we are 
somewhere on the circle, which is called a circle of equal altitude. 

By measuring the zenith distances of two stars at very close 
intervals if we are on a moving ship, or at our leisure if we are 
stationary, we get two intersecting circles and must be at one of the 
points of intersection. For most purposes, this will be sufficient. In 
practice we are not likely to be so ignorant of our position as not 
to know which of the two points of intersection is the right one. If, 


however, we are totally lost we can always measure a third star, 
and the three circles will only meet at one point. 

Practical navigation is, of course, not done in this simple way 
with a globe. A chart is used, and various allowances are made, as 
well as using calculation in place of simple measurement. 

A sextant needs to be corrected for the dip of the horizon, that 
is to say, the height of the eye above the horizon ; but, for practice, 
a home-made astrolabe can be used, and this makes its own 
artificial horizon. Alternatively, for those who are not handymen, 
a bubble sextant can be used, though it requires a good deal of 
practice to become proficient in the use of this instrument. A 
further correction has to be made for refraction; but, if a star not 
too far from the zenith is used, the effect can be ignored. If the Sun 
is the chosen body, it is easier to measure from the lower limb than 
to try to find the centre point. In this case a correction of about a 
quarter of a degree has to be made for the semi-diameter. 

These adjustments are relatively simple. The main toil of prac- 
tical navigation is working out a solution instead of measuring it 
on a globe. The method is simple enough in theory, but requires 
elementary spherical trigonometry; four-figure log tables, more- 
over, are not accurate enough, so the scope for error is sufficiently 

The method used in principle can be seen from the drawing. Let 
C be the position of the ship, A the pole, and B the zenith position 
of the star used. Then c is clearly the polar distance of the zenith 
point; that is 90° minus the latitude, and a is the zenith distance of 
the star, as measured. 

From dead-reckoning since the last fix, the approximate longi- 
tude of the ship will be known. To begin with, one takes the angle 
A as being this longitude less the longitude of the zenith position. 
It is required to find b, which is the polar distance of the ship, i.e. 
its latitude subtracted from 90°. This is given by the equation : 

cos a = cos b cos c + sin b sin c cos A 

Having worked this out, one can mark the position deduced on 
the chart. This is the position of the ship if the assumed longitude 


A (North Pole) 

is correct. The process is then repeated, assuming a slightly 
different longitude, and deriving a slightly different latitude. This 
point is also marked on the chart and a line is drawn passing 
through the two points and extended a little in both directions. 
Though, for practical purposes, one draws a straight line, the 
points fall theoretically on the arc of a circle of equal altitude ; but, 
on the scale of charts used in practice, the error is extremely small 
and is ignored. 

As with the circle of equal altitude which we traced out on the 
globe, this line on the chart will not tell us our exact position, only 
that we are somewhere on it. Generally, however, it is sufficient to 
correct a dead reckoning position. If it is not, a second reading can 



be taken with a second star, and a second line drawn, the position 
of the ship being at the point of intersection. Alternatively a second 
reading can be taken with the same body later on, and the first line 
adjusted for the movement of the ship during the interval. When 
the Sun is being used, this is necessarily the method employed. 

Recently, extensive tables have been worked out, for a selected 
number of celestial bodies, which are so comprehensive in their 
information that very little calculating is necessary - it is not even 
an advantage to be able to identify particular stars. Beyond this, 
and especially for planes, a great deal of navigating is done by 
electronic aids which have no connexion with astronomy. Even 
using stars, telescopes can now be made to lock automatically on 
to quite faint stars in daylight, and do most of one's navigation for 

In spite of all these modern developments, however, there will 
always be times and places at which these aids are not available, 
and a knowledge of the principles of astro-navigation will be 
required for a long time to come. 

Whatever the future may bring, it is a fact that a study of the 
heavens has guided man in his travels for thousands of years. 
When we take to space travel as part of the ordinary course of our 
daily lives, the one thing which is certain is that a wide and precise 
knowledge of the motions of celestial bodies will be an absolute 
requirement for the safety and convenience of the cosmonauts. 

The Surface of Saturn 


Since the advent of telescopic astronomy with Galileo in the early 
seventeenth century the planet Saturn has been an object of par- 
ticular interest in that it provides us with a fascinating spectacle 
which so far as we can observe is unique among celestial bodies. 
To Galileo, with his pioneering but very imperfect telescopes, 
Saturn presented a considerable problem when it came to explain- 
ing the cause of this strange new phenomenon to the satisfaction of 
his sometimes very critical students. He may have made an inspired 
guess in his later life as to the reason, but the riddle was finally 
solved by Christian Huygens, using improved optical equipment 
of his own design. About the mid-seventeenth century he was able 
to demonstrate that the slow-changing, peculiar appearance of 
Saturn was due to the presence of a vast, flat ring which encircled 
the planet, inclined to the plane of its path around the Sun. The 
attention of these early observers was therefore concentrated upon 
deducing the nature of this fantastic appendage concerning what 
was then the most distant known planet. Indeed, even if they had 
so wished, it is doubtful if their telescopes would have been equal 
to the task of investigating the surface appearance of the globe of 
Saturn. Cassini, a contemporary of Huygens, is thought to have 
been the first to record some surface markings. From the work of 
the few observers who possessed instruments of a sufficiently high 
standard, it became evident that the surface of Saturn was charac- 
terized by dark belts parallel with the equator and the plane of the 
rings. These were similar to the belts visible on Jupiter, a much 
easier observed object, but less dark and conspicuous. 

Very little was contributed in observations of the global features 
from this period until that great and celebrated observer, Herschel, 


examined the ringed planet with his powerful reflecting telescopes 
in the latter half of the eighteenth century. He it was who really 
roused interest at this time in probing the nature of the planet and 
rings, with the aid of these very fine telescopes which he was 
producing. Firstly he was able to say that the belt markings were 
of a variable nature, indicating that we were probably looking at 
cloud formations in some kind of atmosphere. Observational 
proof was then supplied that the outer part of the globe was indeed 
gaseous, by his careful study of what was seen on occasions when 
one or other of the moons of Saturn was due to pass behind the 
body of the planet as viewed from Earth. Direct evidence of the 
airless nature of our Moon is provided by the behaviour of stars 
when occulted. As they pass from our view, the effect is instan- 
taneous, as though someone had snapped off a switch. The effect 
of occultation of a bright object by Saturn is quite different, as 
Herschel observed. Not only did the brightness of the occulted 
moon fade away slowly, with marked fluctuations at times, but it 
was seen to 'hesitate', as it were, on the limb of the globe for some 
minutes after it should theoretically have disappeared. This was 
due to the light being refracted or 'bent' in passing through the 
outer layers of the Saturn atmosphere. Recognition of discrete 
markings on the globe, in the form of patches and spots, revealed 
that the planet rotated fairly rapidly, and by further shrewd 
observation Herschel made an estimate of the rotation period 
which is remarkably close to the value adopted at the present time. 
Also the considerable flattening or compression of the globe 
through the polar diameter was established and very carefully 
measured by him. All this aside from his valuable discoveries and 
observations concerning the ring system and satellites! Those who 
make a study of the magnificent Saturn today owe a great deal to 
the patient work of the great Sir William Herschel, for the very 
considerable store of knowledge which he established. 

Direct observation since then has largely consisted of confirma- 
tion and refinements in measuring these various characteristics of 
the body of the planet. During the present century, however, it has 
been possible to employ another very valuable technique to permit 


an analysis of the atmosphere of Saturn - the use of the spectro- 
scope in conjunction with very large telescopes. Space does not 
allow a detailed description here, but briefly a spectroscope is an 
instrument which enables us to sort out the components making 
up the total visible light from a given source, in terms of standard 
wavelengths. Many substances can be identified readily from the 
characteristic pattern or, to use the correct term, spectrum of light 
which they produce, on comparison with spectra produced under 
laboratory conditions. The Moon and planets shine by means of 
the 'borrowed' light of the Sun, and what we normally see in the 
spectroscope is merely a fainter replica of the Sun's spectrum. The 
dark lines against the band of continuous colour denoting the 
absorption of certain radiations by gases in the outer layers of the 
Sun is faithfully reproduced, along with those introduced in pass- 
ing through the atmosphere of Earth. It was noticed in the early 
part of this century that when the light reflected from Saturn is 
examined in this way, dark bands are seen obscuring certain 
regions of the spectrum, which can have been introduced only 
during the passage of the light through the outer atmosphere of 
Saturn. Many years ensued before laboratory researchers were 
able to show that the effect was due to the light having encountered 
a considerable quantity of methane gas on its journey. This is a 
compound of hydrogen and carbon, which we know on Earth as 
marsh-gas, and is familiar to the miner as the deadly 'fire-damp', 
which, owing to its combustible nature, has been the cause of many 
pit disasters. 

The presence of this gas on Earth is a consequence of decom- 
posing vegetation, but on the Giant Planets such as Saturn is the 
result of the combined effect of very low temperature and great 
mass enabling these objects to retain virtually the whole of their 
original gaseous surroundings. There is no reason to doubt that all 
the major planets in the Sun's family had a common origin, and 
that therefore Earth also once possessed such a dense, unpleasant 
atmosphere. As a consequence of the much smaller mass of Earth, 
the lighter gases in this original atmosphere have leaked away 
steadily into space, leaving us with our present gaseous shroud 


consisting almost entirely of nitrogen and oxygen, the latter con- 
stituent being enriched in supply by the large amount of vegetable 
growth. It came as no great surprise when these hydrogen com- 
pounds were discerned in the atmosphere of Saturn. The total 
amount of material involved, or in other words the mass of the 
planet, could be estimated quite accurately by careful observation 
of the motion of the satellites, all the nine now known having been 
discovered before the end of the nineteenth century. This mass 
proved to be 95-2 times that of the Earth. Yet the volume of 
Saturn is no less than 763 times that of our planet! Obviously 
Saturn is made in the main of much lighter material than the 
terrestrial globe, and hydrogen, the lightest of the elements, fills 
the bill very nicely. Unfortunately, free hydrogen does not reveal 
itself in the spectrum of the light reflected from Saturn, but only 
when it has combined with carbon to form methane (CHJ, and to 
a lesser extent, with nitrogen to form ammonia (NHg). 

One of the most popular and widely accepted theories for the 
probable constitution of Saturn is the model proposed by Dr 
W. H. Ramsey of Manchester University, in the early 1950s. He 
believes that possibly as much as 70 per cent of the mass of Saturn 
consists of hydrogen in some form or other. A fairly shallow 
atmosphere in proportion to the size of the planet is anticipated, 
consisting largely of hydrogen and helium, with the addition of a 
good percentage of methane and a trace of ammonia. At a depth 
of only a few hundreds of miles in this atmosphere the hydrogen 
would be compressed into a solid state, after reaching a consistency 
more like that of a liquid, viscous ocean than an atmosphere. At a 
distance of about 12,000 miles from the periphery of the globe 
toward the centre, the pressure is sufficient to cause a transition 
from the solid to the metallic state of hydrogen. The central core of 
the globe probably contains some of the heavy elements such as 
form the body of our planet Earth. This, with the great proportion 
of metallic hydrogen, gives a probable density at the centre of 
Saturn of about 1 -9 times that of water. The mean density of 
Saturn, which is calculated from our direct knowledge of the 
size and mass of the globe, is only 0-69 times that of water. 


Saturn is therefore by far the lightest of the planets per unit 

So much, then, for the reasons, both theoretical and observa- 
tional, for believing that in the case of Saturn we are looking at a 
very different kind of world as compared with planets such as 
Earth and Mars. Nevertheless, we do observe this familiar charac- 
teristic of a cloaking atmosphere, though sufficiently deep and 
dense to prevent observation of whatever kind of solid surface 
might exist. 

It was suggested in the early days of telescopic observation in 
astronomy that the giant planets, particularly Jupiter and Saturn, 
might have some radiation output of their own, to account for the 
brightness of these objects, and the atmospheric turbulence and 
upheaval which is observed. However, modern measurements of 
temperature and radiation levels of these planets, together with 
theoretical considerations, makes it almost certain that the belt 
markings, spots, and other detail seen are due to the action of the 
Sun, in just the same way that the depressions, anti-cyclones, 
hurricanes, and great weather movements in Earth's atmosphere 
are generated in the first place by the solar 'heat-engine'. So there 
is a surprising, and in some ways unexpected, similarity in the 
behaviour of the clouds of Earth and Saturn. Though the clouds of 
Saturn may be of quite different composition to those we are 
accustomed to, yet they serve to trace out the movements in the 
atmospheric envelope under the influence of temperature differ- 
ences and the rotation of the planet. The rotational velocity of 
Saturn is high, the 'day' being only 10 h 14 m at cloud level at the 
equator. This swift rotation and strong central concentration of 
mass combine to produce the pronounced flattening of the globe 
through the poles of rotation. 

Anyone who has studied Saturn at all will have heard of the 
Great White Spot of 1933. This was discovered by Will Hay, 
otherwise famous in the entertainment world, in August of that 
year, on the Equatorial zone of Saturn. This marking was followed 
for over five weeks by the leading planetary observers of the time, 
and its behaviour was typical of other spots or discrete markings 


which have been seen on the planet on rare occasions. After dis- 
covery, the spot lengthened steadily in the direction of the planet's 
rotation, and the preceding end became blurred and indistinct after 
only a few days. This carried on until the 'spot' extended almost 
half-way round the equator of Saturn. At the same time the 
rotation period of this particular feature shortened. This and 
similar instances seem to indicate that the outer parts of the atmo- 
sphere rotate faster than the lower levels, or in other words, there 
is the semblance of a wind in the direction of rotation. As the 
material forming the spot moves upward in the atmosphere, so it is 
carried forward round the planet parallel to the equator. Some 
spots in the temperate regions of Saturn have been seen to accel- 
erate to a period as short as 9 h 55 m , or about equal to System II on 
Jupiter. Doubtless they also have risen in the atmosphere, and 
have steadily advanced with respect to the normal cloud-level. The 
belts are also formed and maintained most probably in this 

One cannot escape an intriguing comparison here with the so- 
called 'jet streams' in the atmosphere of Earth. These powerful 
east-moving winds have become known since the inception of 
high-altitude flight, and have been used by east-bound aircraft to 
establish record times in transit from one continent to another. 
Hence they are accelerated in the direction of Earth's rotation! 
Situated in median latitudes north and south of the equator, the 
jet streams are found by their particular temperature characteristics 
and if they were delineated by clouds, as they sometimes are over 
part of their path, they would appear from space rather like the 
N. and S. Equatorial Belts of Saturn do to us. There is even a 
lesser sub-tropical jet stream, which could appear as a fainter belt 
marking closer to the equator. Further careful observation and 
measurement of the latitudes of the belts on Saturn will establish 
in time whether they move toward or away from the equator in 
rhythm with the seasons, as these fast-flowing streams in Earth's 
upper atmosphere do. 

Lastly, what is the prospect for future space-travellers who may 
choose to visit the planet Saturn? Certainly they would be advised 


not to try to find the solid surface of the globe, beneath the deep 
and dense atmosphere, for the pressure at the real surface of solid 
material is estimated to be many times that at the deepest points in 
Earth's oceans. A much more interesting and healthy way of 'taking 
in the view' would be to float in the atmosphere at about cloud- 
level by using containers of de-compressed hydrogen or helium. 
Protection would be needed from the very low temperature at this 
level of around - 120°C, but weight would present no problem, 
things being much the same in this respect as they are at Earth's 
surface. The force of gravity on Saturn at upper atmosphere level 
is only a little greater than that on the Earth's surface. Our 'Saturn 
balloonist' will now be carried around by the rotation of the 
planet, and we must assume that he has been wise enough to avoid 
being placed in the region beyond latitude 63 degrees N. and S., 
roughly corresponding to the Arctic and Antarctic Circles of 
Earth. Here the Sun would not be seen for long periods, up to 
almost 15 of our years in extreme cases, and the glorious spectacle 
of the ring system would be below the horizon, permanently 
hidden from view. These conditions follow naturally from the fact 
that the axis of rotation of Saturn is inclined to its orbital plane a 
little more than that of Earth, around 27 degrees, the planet takes 
29| years to orbit the Sun, and the ring system is in the plane of the 

Imagining the choice of latitude to be his, a far better idea for 
our explorer would be to position himself somewhere in temperate 
latitudes, say about 40-45 degrees N. or S. This would place the 
ring system at a pleasing angle of view for detailed study, forming 
a great arch spanning the heavens, and undergoing fascinating 
transformations of light and shade during the Saturnian year. He 
would experience a 'day' of about 10i hours, and for many Earth- 
years the Sun would be placed behind the rings, its light being 
delicately veiled to a varying degree, brightening as it traversed the 
so-called ring divisions. The Sun in the Saturn sky would be a tiny, 
brilliant object, having only one-ninth of the diameter which it 
presents to us, or between 3 and 4 minutes of arc. Also it could 
never be entirely eclipsed by the rings as seen from these latitudes, 


but would continue to show quite well through even the thickest 
portions. For a region just a few degrees N. and S. of the Saturn 
equator only would the rings be able to completely obscure any 
celestial body, including the Sun. During the summer in a par- 
ticular hemisphere, with the Sun well above the plane of the rings, 
they would form a broad silvery band, against a rather bright sky 
background due to scattered light in Saturn's considerable outer 

At night the portion of ring visible when the Sun is above the 
ring plane to the observer would bear a dark wide gap as though a 
section were missing. This is the effect of the intensely black cast 
shadow of the globe obscuring the Sun's light from the opposing 
part of the ring system. This would reach a maximum in extent 
when the Sun lies in the plane of the rings, on two occasions in the 
Saturn year. At midnight there would be a brilliant arc of ring 
reaching up from east and west horizons, with an apparently clear 
gap in the S. or N., according to the hemisphere in which the 
observer was placed. On closer inspection, it would be realized 
that only the brighter stars are visible to the unaided eye in this 
region of sky, due to the filtering effect of the ring particles. Closer 
to the equator, of course, the rings seen at a shallow angle would 
cause a strip of sky to be quite blank of stars. The appearance of 
the rings at night during the winter in either hemisphere would be 
fascinating indeed, with the Sun shining through the ring from 
below. Thicker portions of the rings would be outlined as bright 
and slender concentric arcs, and the effect would be one of very 
subtle tones as the angle of the sunlight to the ring plane varied, 
imagining each ring particle to behave like a tiny replica of our 
Moon, passing through a slow succession of phases. Then there 
would be the spectacle of several of the moons of Saturn moving at 
varying speeds across the night sky, against a background of con- 
stellation patterns which would appear just the same as we see 
them from Earth. 

Our seemingly great leap through space from the orbit of Earth 
to that of Saturn is infinitesimal when compared to the distance of 
even the nearest stars comprising these familiar groups. Merely to 


have this privilege of a wonderful new outlook on the solar system 
from the surface of the most magnificent planet in that system 
should be ample reward for a journey from Earth which would 
take at least about 4 or 5 of our years. However, we must leave our 
hardy adventurer with a problem to consider - how to build up a 
velocity of 22 miles per second to escape from the gravitational 
hold of the planet and return home ! 

Planetary Nebulae 


'Planetary nebulae' was the name given by William Herschel in 
1785 to objects which appeared in his telescope as tiny disks of 
light with a hazy or nebulous edge. They looked greenish in colour 
and not so very different in appearance from the distant planet 
Uranus, which Herschel had discovered four years earlier. Yet, 
whatever magnification he used, the objects always showed an ill- 
defined edge, just as if they were nebulous disks of a 'much- 
condensed, luminous fluid'. In brief, Herschel found it impossible 
to decide exactly what these objects were, and he adopted the term 
planetary nebulae simply because it described what he saw. We 
still use the same name, even though we know, as did Herschel, 
that the objects are certainly not planetary. 

Yet if planetary nebulae are not planets, and not straight- 
forward gaseous clouds - what Herschel would have described as 
'luminous fluid' and called 'nebulae' pure and simple - what are 
they? Why do they present primarily a greenish appearance, and 
why do they appear round or oval, instead of being spread 
irregularly over a patch of the sky ? The answer is that all planetary 
nebulae are associated with a bright central star, and the hazy disk 
is composed of gas surrounding the star. Indeed, we shall not be 
very far from the truth if we think of a planetary nebula as a star 
with an immense gaseous shell of atmosphere extending around 
and spreading outwards in space for millions of miles. 

Some hundreds of planetary nebulae are known, but all are so 
far off that none are bright objects in a telescope. Every single one 
is only a dim hazy patch at first glance. It was, of course, this fact 
that caused Charles Messier to include some of the brighter ones in 
his great catalogue of nebulae ; a catalogue which he drew up for 


the sole purpose of helping comet observers, so that they should 
not become confused between nebulae and the dim hazy patch of 
light which a comet shows when it is still some distance from the 
Sun. So if we try to observe planetary nebulae, we shall be examin- 
ing very faint objects indeed. The most spectacular of them is 
probably the 'Ring' nebula, M57 (number 57 in Messier's cata- 
logue), which is to be found between Beta and Gamma Lyrae. It has 
a central star which is not visible at all in a small telescope, and a 
bright ring of gas, rather like a bright round doughnut. The central 
star of the 'Owl' nebula (M97) is also quite invisible in all but a 
large telescope, although its faint hazy disk which appears about 
the size of Jupiter can be seen. It was Lord Rosse who coined the 
name 'Owl' for the nebula, because in his giant 72-inch telescope 
the disk seemed to have two slightly darkish patches, one each side 
of the centre, and just like the dark patches made in its white face 
by the eyes of a barn owl. 

The very dimness of planetary nebulae means that every 
observer will record an object differently, depending upon his own 
eyesight. In consequence, the only really satisfactory way of study- 
ing these objects is to use photographs made with very large 
reflectors. And, of course, astronomers want to know the nature of 
the gaseous envelope surrounding the central star. Is it moving, 
and if so how? Of what gases is it composed? How hot is the cen- 
tral star, and why does the surrounding envelope glow? To answer 
these and many other related questions requires the use of the 
spectroscope, but this is not easy, because of the dimness of the 
nebulae. However, using newly designed spectographs attached to 
the 100-inch and 200-inch telescopes has recently provided a great 
amount of new information. 

The central star of every planetary nebula so far observed is 
certainly extremely hot. In fact, recent studies have definitely 
established that their temperatures are never less than 25,000°C. 
Some are a type of star known as class W or Wolf-Rayet type, after 
the two French astronomers who first examined stars like this in 
detail. They are bright, very hot stars which radiate their energy 
away at terrific rates, and may well be surrounded by expanding 


shells of gas. However, the Wolf-Rayet stars at the centre of 
planetary nebulae seem to be different from normal stars of this 
type; they are dimmer and although bluish stars, show every 
evidence of being old. The second type of star to be found at the 
centre of planetary nebulae is also believed to be old, containing, 
like the other type, more helium than hydrogen. These are the O 
type, bluish-white stars, which are again intense energy radiators. 
Both the W and the O stars which are found in all planetary 
nebulae are small, and it seems likely that they are blue or white 
dwarf stars. In consequence they will be very massive - with their 
material so intensely packed together that a matchbox full of it 
would weigh something like a ton! Surrounding these stars is some 
gaseous material which is at an amazingly high temperature, due to 
the intense radiation from the central star. Thus some recent 
measurements have indicated that 100,000 C C. is not unusual for 
the nucleus of a planetary nebula, and one nebula, NGC 7662 
(number 7662 in the New General Catalogue of nebulae) may, it is 
believed, have a nucleus temperature of 200,000°C. 

The gases which surround the star and form the nebular part of 
the object, are very widely spread out indeed. In fact, their general 
density is much lower than what we would call a vacuum on Earth, 
with only something like 16 atoms per cubic inch. Perhaps we can 
best see what this means if we imagine taking the air from an 
ordinary toy balloon and spreading it out so that it filled a balloon 
which is 45,000 miles in diameter - that is a balloon 8| times as 
large as the Earth. Only then would the air be dispersed in a way 
equivalent to the gas in a planetary nebula. 

Tenuous the gas may be, but it is spread over a considerable 
volume of space. Most planetaries have diameters of about half a 
light-year, although some of the larger may possess diameters of 
two light-years or more. However, we must treat these figures with 
reserve. They refer to the observed diameters of the nebulae, but 
there are reasons to suppose that the gases may well extend farther 
out than this. Whether or not they do depends really upon the way 
in which the planetaries shine, and this we must now consider. 

The gas of a planetary nebula shines because of the star at its 


centre. As we have seen, such a star is very hot and has an absolute 
magnitude of between and — 1, that is about 100 times as bright 
as the Sun. Even so it has become clear that most of its radiation is 
not in the visible region of the spectrum at all. In fact, it has been 
found that these W and O type stars are more efficient radiators of 
ultra-violet than of any other radiation, and so the gaseous 
envelope of a planetary nebula is constantly receiving an intense 
stream of ultra-violet light. This radiation is of high energy, and 
consequently it has a marked effect on the gas atoms. It causes 
them to become ionized, that is to say it causes them to lose one or 
more electrons, and much of the radiation we observe is due to the 
re-combination of these free electrons with the ionized atoms or 
ions. The really remarkable thing about all this is the degree of 
ionization which takes place. As we might expect, the most intense 
amount occurs close to the central star, and is so great that atoms 
of the gas neon, for instance, which is hard to ionize, are ionized 
four times - in other words, lose four of their electrons. Farther 
out the ionization is a little less, but even so oxygen atoms have 
been stripped of two electrons, and neon is in a similar state. In the 
most distant regions, singly ionized oxygen is still to be found. 
These ionized atoms all emit radiation in the visible part of the 
spectrum. The Danish astronomer, Bengt Stromgren, believes that 
all we can photograph is the ionized gas of a planetary nebula. 
Should there be neutral (unionized) gas lying farther out from the 
central star and well beyond the ionized envelope, then he believes 
that this will not be observed. If he is correct, our estimates of the 
diameters of planetary nebulae must all be too small and require 

Ionized gas atoms are not the only source of visible radiation 
from the nebulous material. Because the gas is so thinly spread out 
over so large a volume of space, many of the electrons which are 
torn away from their parent atoms by the ultra-violet radiation 
will move freely about before re-combining with the ionized atoms. 
These electrons may lose energy when passing close to an atom, 
even though they do not re-combine with it. Such a loss is observed 
as visible radiation, and so adds to the light we received from the 


nebula. What is more, the very tenuous conditions of the gas result 
in some atoms remaining in a kind of temporary state as far as 
their energy is concerned. Only after an appreciable fraction of a 
second will such atoms return to normal, emitting radiation as 
they do so. In brief, then, the atoms of the gas of a planetary 
nebulae undergo much disturbance due to the ultra-violet radia- 
tion from the central star : as a result they emit visible radiation. 

The shape of planetary nebulae varies widely. Besides the more 
normal kind of ring and disk types, there are those in which the 
surrounding nebula is egg-shaped or even more elongated. The 
'Dumb-bell' nebula in the constellation of Vulpecula (the Fox) is 
an excellent example. Some investigators believe that an irregular 
shape is more frequent and more likely, and it has even been 
suggested that some of the regular ring and disk nebulae are really 
elongated clouds viewed from one end. Certainly it now seems 
clear that the gases are not evenly distributed about the central 
star. In some areas they are more closely packed than in others, 
while under high magnification in a very large telescope the sur- 
rounding material often seems to be composed of many strands or 

None of the planetary nebulae are close, and their distances are 
in general thousands of light-years from us. Moreover, they are far 
from being evenly spread over the sky. Instead, they show a very 
definite concentration towards the central area of our own Galaxy, 
spreading all round it in the shape of a flattened disk. If we think of 
our own Galaxy as shaped rather like two soup-plates placed 
mouth to mouth, then we must picture the planetary nebulae 
spread out over a small plate placed at right-angles, and so stretch- 
ing above and below the soup-plates. The closer to the centre of 
the Galaxy we get, the more planetary nebulae there are, and by 
far the greatest number are to be found concentrated within a 
distance of 5,000 light-years from the centre. Beyond this distance 
they rapidly thin out. 

How the planetary nebulae were formed, no one knows. Most 
investigators seem agreed that the gaseous material has been 
ejected from the central star, for it is always observed to be moving 


outwards. Even the fact that so many planetary nebulae are 
irregular in shape does not alter the case. The pressure of the 
radiation from the central star and unevennesses in the gas itself 
would soon lead to distortions of the gas envelope, even if it were 
originally shaped like a perfect sphere. 

One is tempted to suppose that every planetary nebula is, 
perhaps, the result of a nova-explosion of a dwarf star late on in 
its life. Yet more evidence about the way in which stars evolve and 
about planetary nebulae themselves is really needed before we can 
achieve more than a guess. 


Harrison, Maskelyne and the 
Longitude Problem 


It is just two centuries since a solution was found to the problem of 
finding a ship's longitude at sea by practical methods. 

As early as 1714 'An Act for Providing a Publick Reward for 
such Person or Persons as shall discover the Longitude at Sea' was 
passed. This Act appointed Commissioners, who constituted the 
Board of Longitude, and laid down that if a method was con- 
sidered by these Commissioners to be of general use and prac- 
ticability, then the inventor would be 'Entitled to a Reward, or 
Sum of Ten Thousand Pounds, if it Determined the said Longitude 
to One Degree of a great Circle, or Sixty Geographical Miles; to 
Fifteen Thousand Pounds, if it Determined the same to Two 
Thirds of that Distance; and to Twenty Thousand Pounds if it 
Determined the same to One half of the same Distance'. It was 
stipulated that half of any reward was to be paid when a majority 
of the Commissioners agreed that it would be useful to navigation, 
the other half to be paid when the method was proved by a voyage 
between Great Britain and the West Indies. 

The two methods most likely to succeed in finding the longitude 
were, first, the construction of an accurate timekeeper, which 
could be carried by a ship, giving the time of a standard meridian 
of longitude, for example, Greenwich. Local time could be 
obtained by fairly simple observations. As the longitude of the 
ship would be the difference between the meridian on which she 
lay and that of Greenwich, this method would lead to a simple 
solution. At this period, however, there was no timekeeper capable 
of keeping anything remotely like accurate time at sea. 

The second possibility depended on the navigator having 


accurate positions of the Moon and stars. If these were known, 
tables could be calculated, giving the Moon's angular distance, as 
observed on a standard meridian (again, say Greenwich) from 
selected fixed stars. If, by means of a suitable instrument, these 
distances could be observed from shipboard, then the correspond- 
ing Greenwich time could be obtained from the tables. Even 
though the sextant, or, more strictly, quadrant at first, was inven- 
ted independently by Hadley in this country and Godfrey of 
Philadelphia in about 1730, no accurate tables of the positions of 
the Moon and stars were available in suitable form. 

For more than two decades after the formation of the Board of 
Longitude no reasonable method was suggested, but in 1737 John 
Harrison (1693-1776), son of a Yorkshire carpenter, proposed a 
promising plan for a marine chronometer. Financially assisted by 
the Board, he constructed over the years three large timekeepers, 
the third being completed in 1757. At this stage Harrison notified 
the Board that he intended to enter it for the £20,000 reward and 
also intended to construct a fourth and much smaller watch. 

Harrison's genius produced his fourth chronometer, often 
referred to as H4, in 1759; it is probably no exaggeration to say 
that this was (and remains) the most significant watch in the world. 
As far as Harrison was concerned, the time was fast approaching 
when the solution of the longitude problem was in sight. 

A supporter of the lunar distances method had already entered 
the field in 1756, when, at a meeting of the Board on March 6, 
tables of the Moon's places were submitted by James Bradley, the 
Astronomer Royal. A professor at Gottingen University, Tobias 
Mayer, had based these tables on his improved theory of lunar 
motion and had sent them to Bradley for his consideration. The 
Astronomer Royal laid them before the Board with strong recom- 
mendations as to their probable use in determining longitude, as a 
result of which it was resolved to have three of Hadley's quadrants 
made for shipboard observations and that three naval commanders 
should try out the practicability of the lunar distance method. 

Harrison finally decided to stake his reputation and the prize on 
chronometer No. 4 alone ; elaborate precautions were consequently 


taken both by Harrison and the Board to ensure a fair test. On 
1761 March 12 it was decided that Harrison's son, William, should 
accompany the watch (with, of course, an official observer 
appointed by the Board) on H.M.S. Deptford from Portsmouth to 
Jamaica. Sailing on November 18, the ship touched at Madeira 
and arrived at Jamaica on 1762 January 21. Time had been deter- 
mined by the equal altitudes method at Portsmouth and the same 
method was used on arrival in the West Indies. Allowing for H4's 
known rate, it was found that the error only amounted to 5 
seconds slow, or If minutes of longitude (less than one geograph- 
ical mile at the latitude of Jamaica). 

On the face of it, the longitude problem was solved, and 
Harrison was entitled to the full £20,000, but when the results of 
the trial were presented to the Board on June 3 the Commissioners 
had their doubts as to whether the watch's wonderful performance 
was mere chance, and only awarded Harrison an advance of 
£2,500, £1,500 to be paid immediately; the other £1,000 would not 
be paid until a second trial. At the same meeting a petition was laid 
before the Board by Nathaniel Bliss, Bradley's successor as 
Astronomer Royal, on behalf of Mayer's widow (the professor 
having died). 

The beginning of 1763 saw Harrison little nearer his goal, 
although further evidence had been presented to the Board by at 
least one naval commander who had tried out lunar distances in 

It was at this stage that Nevil Maskelyne (1732-1811), whose 
name will always be associated with navigational aids, entered the 
lists. After being ordained in 1755, he had collaborated with 
Bradley on the problem of refraction and soon gained a reputation 
as an able astronomer and a practical observer. Soon deciding that 
the Church was not his real bent, he devoted much time to 
astronomical matters, was elected F.R.S. and selected by the 
Royal Society to observe the Transit of Venus on 1761 June 6 at 
St Helena, the primary object of this expedition being to determine 
the solar parallax. Sailing in the East Indiaman Prince Henry 
under the command of Charles Haggis (not H.M.S. Sea Horse as 


usually stated), Maskelyne stayed ten months on the island and 
made many observations of longitude there as well as on the 

Now, in 1763, he came out fully on the side of lunar distances, 
which he introduced in his privately printed publication 'British 
Mariner's Guide' and in which he strongly advocated the pub- 
lication of an astronomical ephemeris. 

At a meeting of the Board held on 1763 August 4 Harrison 
again requested that No. 4 only should be used on the second trial. 
Arrangements were then made, as on the previous occasion, for 
time determinations at Portsmouth and Jamaica. Reflecting tele- 
scopes (probably Hadley's) and equal altitude instruments were 
again agreed upon as the most suitable means of accurate observa- 
tions. As a result of a further petition on behalf of Mayer's widow 
(this time by the University of Gottingen and the Royal Academy 
of Sciences there) the Board decided that whoever went out to 
Jamaica to make the necessary observations of longitude should 
also make observations of the Moon's motion to test the accuracy 
of Mayer's tables. On being asked whether he would undertake 
this, Maskelyne refused to go to Jamaica on health grounds, but 
said that he would go to Barbados or any other place. To this both 
Harrison and the Board agreed ; Maskelyne was to have £300 for 
his trouble and was eventually accompanied by Green, assistant to 
Bliss at the Royal Observatory, who was made up to Purser of a 
fifth-rate warship (for purpose of payment) and granted his 
expenses. William Harrison and his H4 were to sail in H.M.S. 
Tartar. Maskelyne and Green made the voyage in H.M.S. Princess 
Louisa, the former as chaplain of the vessel, sailing earlier than 
H.M.S. Tartar in order to set up the field observatory at Bridge 
Town, Barbados, for the purpose of redetermining the longitude 
and checking H4 on arrival. This, and making observations on the 
voyage for testing Mayer's tables, was Maskelyne's first duty; it is 
sometimes said that he sailed with H4 to record its performance. 
As can be seen, this was impossible. 

Maskelyne noted in his journal: '. . . (Monday) May 14 
(1764). Early this morning Mr Harrison brought his Timekeeper 


on shore and I took equal altitudes of the sun's limbs, noting the 
time by it as follows. . . . Timekeeper 4 h l'15"-53 faster than 
Mean Time by the meridian of the observatory.' 

On the return voyage from Barbados, the observations were 
laid before the Board on 1764 September 18. 

Maskelyne was paid his £300 and £242. Ss. lOd. expenses; in 
addition he was allowed to sell the materials from the observatory 
building in Bridge Town to pay for his passage and for the freight 
charges on the instruments. Later, owing to the materials only 
realizing £18. 10s. Ad., the Board paid him a further £87. 12y. 1\d. 
to make up his expenses. 

By January 19 the observations had been reduced by four inde- 
pendent persons and H4 was found to have an error of 38 seconds 
fast in seven weeks, corresponding to less than 10 geographical 
miles. Maskelyne, to be officially appointed Astronomer Royal in 
about a fortnight's time, was entrusted with Mayer's tables. 

Harrison, on his watch's second success, now asked the Board 
for a certificate to enable him to receive the full reward. On 1765 
February 9 the Commissioners declared themselves 'unanimously 
of the opinion that the said Timekeeper has kept its time with 
sufficient correctness and without losing its longitude in the voyage 
from Portsmouth to Barbados beyond the nearest limit by the Act 
of 12 of Queen Anne, but even considerably within the same'. 
They stipulated, however, that the principles of the watch should 
be disclosed, although they did request Parliament to make up the 
money already advanced to £10,000 (excluding the advances for 
improvements) and pay the balance 'on proof being made to the 
satisfaction of the Board that his method will be of common and 
general utility in finding the longitude', in other words, that 
similar watches could be readily made. 

At this moment of half triumph and half frustration for 
Harrison, Maskelyne presented a carefully prepared and far- 
reaching memorial to the Board (of which he was now a Commis- 
sioner by virtue of being Astronomer Royal). In it he stated his 
case for lunar distances, supported by evidence of considerable 


On his voyage to St Helena and back he had observed the dis- 
tances of the Moon from the Sun and fixed stars and, by using 
Mayer's tables, made his longitude determinations with errors of 
'not more than a degree'. He had (on the Board's instructions) 
repeated these observations on the recent voyage, had made 
Barbados within half a degree and the Isle of Wight on his return 
within 16 minutes of arc. Strongly urging the general publication 
of Mayer's tables, he stressed the need for an ephemeris, support- 
ing his claim by the evidence of four East India Company Com- 
manders. These officers, who were examined by the Board, had 
used the principles laid down in 'The British Mariner's Guide', and 
stated that their longitude determinations agreed 'within a degree, 
seldom a greater error, each observation taking up not more than 
four hours' time to find'. When questioned, they were unanimously 
of the opinion that 'if a Nautical Ephemeris was published, this 
Method might be easily and generally practised by Seamen'. The 
Board, impressed by this combined onslaught, resolved that 
Mayer's tables should be printed, that his widow should be 
awarded a sum not exceeding £5,000 and that Parliament should 
be asked to 'give a reward to persons to compile a Nautical 
Ephemeris and for authority to print the same, when compiled, in 
order to make the said lunar tables of General Utility'. 

Before the Board met on 1765 May 28 an Act had been passed 
authorizing the payment of £3,000 to Mayer's widow and the 
construction of an ephemeris. At this meeting it was reiterated that 
Harrison must disclose the principles of H4 before being paid any 
part of the second half of the reward, while Maskelyne and the 
professors of astronomy on the Board were asked to consider a 
plan for the production of the ephemeris. 

This all occurred on a Tuesday and by Thursday, May 30, the 
plan was laid before the Board; it was immediately approved and 
Maskelyne instructed to find 'proper persons to perform the cal- 
culations'. These were engaged within a fortnight and it had also 
been decided to print 2,000 copies of Mayer's tables, reduced to 
the meridian of Greenwich. One pair of calculators (Israel Lyons 
and George Witchell, the latter Headmaster at the Royal Naval 


Academy, Portsmouth) were to calculate the almanac for 1767, 
while that for 1768 was to be prepared by John Mapson and 
William Wales. These four were to receive £70 each for their 
services, Maskelyne supplying the necessary books and tables. 

By the spring of 1766, Witchell's own 'General Tables of 
Refraction and Parallax' had been printed, as had Mayer's tables, 
and the ephemeris for 1767, under its title 'The Nautical Almanack', 
was on sale. The time which had elapsed between the presentation 
of Maskelyne's memorial to the Board and the Nautical Almanac 
becoming a reality was thus little more than a year. Its popularity 
was immediate; within a further year the almanac was officially 
distributed to 'all the chief ports in Great Britain and Ireland, New 
York and principal places in America' ; within three years masters 
of all Royal Navy ships were to take courses at the Royal Acad- 
emy, Portsmouth, in the use of the Nautical Almanac and Hadley's 
quadrant and expected to obtain a certificate. 

Harrison, meanwhile, had not been able to persuade the Board 
that he had proved his case entitling him to the other half of the 
£20,000. The wrangle dragged on and the elderly conqueror of the 
longitude problem was to see H4 tested at the Royal Observatory 
for ten months and a copy made by Larcum Kendal before he was 
able to obtain some support from George III in petitioning Parlia- 
ment. At this the Board's opposition collapsed and the remainder 
of the reward (less £1,250 in advances) was paid in 1772. 

Maskelyne received no lump sum for his part in the practical 
solution of the problem, but he did receive an additional salary as 
superintendent of the Nautical Almanac until his death in 1811, 
and lunar distances continued to be published until 1906. 

In spite of Harrison's charges that Maskelyne was seeking 
monetary reward, this seems highly improbable, as does the 
accusation that during the trial of No. 4 at the Royal Observatory 
the chronometer was deliberately subjected to high temperatures 
in the midday sun. To do this Maskelyne would have had to treat 
his Transit instrument in the same way (both were in the same 
room) and he was too able an observer to do that. 

On the other hand, Maskelyne was in a strong position to 


influence the Board of Longitude. From 1765 he was a Commis- 
sioner as a consequence of being appointed Astronomer Royal and 
rapidly became scientific adviser to the Government. He had con- 
siderable private means, and his brother Edmund held high office 
in the East India Company (this no doubt explains bis witnesses, 
whom he called in to support lunars from time to time); his 
brother-in-law Robert, Lord Clive, had been created a peer in 
1762 and a Knight of the Bath in 1764. Clive, then a popular hero, 
was on leave in England before being reappointed Governor of 

The Seven Years War had ended in 1763, Britain having gained 
almost more from the Treaty of Paris than from any other treaty 
in her history. Canada was secured, additional territories gained in 
the West Indies, and France had recognized British dominion in 
Bengal and the Carnatic. With an expanding overseas trade and 
shipbuilding greatly on the increase, this did indeed seem the 
appropriate moment for Maskelyne to launch what was to become 
the greatest single aid to navigation of all time. 

Acknowledgement is made to the Astronomer Royal for his permission to 
use the records of the Royal Greenwich Observatory. 

Editorial Note: Harrison's four chronometers have always been treasured at 
the Royal Observatory (now the National Maritime Museum), but recently 
H4 has made its third voyage across the Atlantic. On 1963 March 8 an impres- 
sive little ceremony was held at the British Embassy in Washington, D.C., 
when the British Ambassador handed over Harrison's fourth chronometer to 
the U.S. Naval Observatoiy on loan for one year. This beautiful instrument is 
shaped like a watch, but is rather more than 5 inches in diameter. The copy 
made by Larcum Kendal, which is referred to in Mr Lauiie's article, was used 
by Captain Cook in his voyages of 1772-5 and 1776-9, and is also preserved at 

The Short-period Comets 


It is usually a surprise to the ordinary reader to learn how many 
comets are seen each year. In the five years 1958 to 1962 no less 
than 42 comets were under observation; of these, 17 were new 
discoveries, while the remaining 25 were all short-period comets 
whose returns had been predicted with sufficient accuracy for them 
to be recovered. The greater number of these recoveries - 18 out of 
the 25 - were made by one astronomer, Dr Elizabeth Roemer, who 
uses the 40-inch reflector of the Flagstaff Station of the U.S. Naval 
Observatory. Miss Roemer endeavours to keep track of all comets 
- especially those fainter than magnitude 17 - and it is largely due 
to her efforts that we have been able to maintain our records of 
these insignificant objects in recent years. There are few observers 
with such skill and experience, and there are few other telescopes 
with time to spare for this class of work. 

A short-period comet, usually represented by the symbol P/, is 
to be regarded as one whose period is comparable with those of 
the planets ; a period of 200 years is considered a suitable upper 
limit. The periods actually range from the 3-3 years of P/Encke 
(with a doubtful 2-3 years for P/Wilson-Harrington of 1949) up to 
the 164 years of P/Grigg-Mellish, which was seen in 1742 and 1907. 
We have on our lists 94 such comets, of which 55 have made more 
than one return to perihelion. They are mostly very faint objects, 
of very little interest in ordinary telescopes, but they offer a 
constant challenge to the computer. 

As a class, they differ from the majority of comets in having a 
more restricted range of inclination to the ecliptic. Whereas the 
majority of cometary orbits may be inclined at any angle, so that 
almost a half of them have retrograde orbits, those of the short- 



period comets are mainly of small inclination, and only seven (one 
of which is a very doubtful case) travel in the retrograde direction. 
The elliptical orbits in which they revolve are quite eccentric, so 
that the perihelion distance is small, but the aphelion distance may 



After Richter, 'Nature of Comets' 


be quite large. There are, however, two comets which are excep- 
tions to this rule, and which have orbits so nearly circular that they 
are like minor planets, and are seen every year at opposition. 
Comet Schwassmann-Wachmann (1), discovered in 1925, has an 
orbit which lies entirely between those of Jupiter and Saturn, and 
it has the smallest eccentricity (0-131) of any comet, and the largest 
value (5-54) of perihelion distance. Comet Oterma travels in a 
smaller orbit between Mars and Jupiter, the eccentricity being only 

The most famous of all these comets is, of course, that of 
Halley. Halley, who was a friend of Newton, and had been largely 
responsible for the publication of the famous Principia, was one of 
the first to realize the full value of the new laws of gravitation. He 
investigated the history of the appearance of comets, and com- 
puted their orbits, and was struck with the fact that the orbit of the 
comet of 1682 (which he had himself seen) was similar to those of 
Apian's comet of 1531, and the comet seen by Kepler and 
Longomontanus in 1607. He also linked these with the comets of 
1456 and 1305, and was thus led to the idea of periodic comets, 
this particular example having a period of about 75 years. He made 
the first rough estimates of planetary perturbations, and the first 
prediction of the return of a comet : 

Hence I think I may venture to foretel, that it will return 
again in the Year 1758. And, if it should then so return, we shall 
have no reason to doubt but the rest may return also : Therefore, 
Astronomers have a large field wherein to exercise themselves 
for many ages, before they will be able to know the number of 
these many and great Bodies revolving about the common 
Centre of the Sun, and to reduce their Motions to certain Rules. 

Halley died in 1742 at the age of 85. Sixteen years later, the 
comet returned as he had foretold, and it is to honour his name 
that we attach it to this fine comet. More accurate predictions were 
made before the actual return by Clairaut and his collaborators 
(the work taking more than two years); predictions for the 1835 
return were made by Rosenberger and others, and that for 1910 by 


Cowell and Crommelin. The comet is next due at perihelion 
towards the end of 1986. 

For more than half a century after its first return in 1758, 
Halley's comet remained unique, but by 1 8 1 8 three periodic comets 
were known, and although we should regard them as having long 
periods they were, in those days, considered exceptionally small ; 
these comets were P/Halley, Pons' comet of 1812 (now known as 
P/Pons-Brooks), and Olbers' comet of 1815. The orbits of these 
had been computed by Gauss or by his pupil Encke. Then in 1818 
Pons, at Marseilles, discovered a faint comet, and Encke calculated 
its orbit. He found a period of 3| years, and showed that this 
comet was identical with those of Mechain (1786), Caroline 
Herschel (1795), and Pons (1805), and, after six weeks of intensive 
work, he predicted the return of the comet in 1822. 

It is difficult for us to realize the intense interest aroused by this 
work of Encke's; not only had he demonstrated the value of 
Gauss's methods, but he had shown the presence of an entirely 
new class of object within the solar system. This was only the 
second prediction of the return of a comet to be made after the 
lapse of nearly a century. The comet was duly recovered in 1822, 
and has made regular returns since then - 46 appearances at peri- 
helion in all - and is due again in 1964. 

Comets are usually named after the observers who discover 
them, but in exceptional cases the rule is not followed, and the 
comets named after Halley and Encke are examples of giving 
honour where honour is due. Another example is to be found in 
P/Crommelin, which was originally known by the cumbersome 
title of P/Pons-Coggia-Winnecke-Forbes. Crommelin showed that 
the comets of Pons (1818), Coggia and Winnecke (1873) and 
Forbes (1 928), were identical, and that the period of 27 years tallied 
with the appearances of comets in 1457 and 1625. The comet was 
renamed in his honour in 1948. 

In his younger days, Crommelin had assisted Cowell in cal- 
culating the behaviour of Halley's comet. Their prediction for 1910 
was only a few days in error - a fine piece of work in a comet with 
so long a period. (It may be as well to point out that this comet was 


a very disappointing object as seen from our latitudes. There was a 
very bright comet that appeared about the same time, and this is 
often remembered by those old enough, who like to delude them- 
selves that they saw Halley's comet in 1910 in the western sky at 
sunset. The comet was seen at its best in the southern hemisphere.) 
In addition to making a prediction for 1910, Cowell and Crom- 
melin also traced the past history of the comet; every appearance 
back to a.d. 989 was confirmed (including the famous one of 1066, 
which is depicted on the Bayeux Tapestry) and all but one or two 
of the returns as far back as 240 b.c. 

The lengthy period of Halley's comet is somewhat unusual, 
most of the short-period comets revolving about the Sun in 6 to7 
years. Of the total of 94 comets, there are 52 which have orbits 
with periods in the range 5 -4 to 8 -0 years, and this corresponds to a 
mean distance from the Sun of 3 to 4 astronomical units, with 
aphelion distances of the order 4 to 6 a.u. Since the mean distance 
of Jupiter from the Sun is 5-2 a.u., these comets may undergo 
severe perturbations by this planet, and this is merely one of the 
many lines of evidence which show the influence of Jupiter on 
cometary orbits. These comets are commonly known as the 
'Jupiter family' of comets, but there is less justification for pushing 
the idea further and speaking of the 'Saturn family' or the 'Nep- 
tune family' of comets. The comets with periods of the order of 75 
years (such as Halley) are supposed to belong to this 'Neptune 
family', but such comets can actually come closer to Jupiter than 
they do to Neptune, because of the inclinations of their orbits. It is 
always the attraction of Jupiter that dominates the behaviour of 
the periodic comets, and this at least must be allowed for in pre- 
dicting the next return to perihelion. 

The effect of perturbations is often misunderstood. If a comet is 
attracted by Jupiter, it does not move towards that planet; it 
remains always under the control of the Sun, and its motion is 
merely deflected to some extent. Now the entire nature of the orbit 
is controlled solely by the velocity (which includes the direction of 
motion, as well as the speed), and if the velocity is altered, then the 
whole orbit is changed. To illustrate this, let us consider just one 


simple case - a direct attraction on the comet in the forward direc- 
tion. Now, it is well known that in an elliptical orbit the speed is 
greatest at perihelion, and least at aphelion - thus Halley's comet 
is near aphelion at present, and its speed is about half a mile per 
second; when it comes to perihelion in 1986 it will be moving at 
almost 34 miles per second. It is also true that a planet in a large 
orbit moves more slowly than one in a smaller orbit - this follows 
at once from Kepler's Laws. But when we come to study- 
ing the numerous intersecting orbits of the comets we meet a 
curious paradox. Suppose we have two bodies - say, a comet and a 
planet - at the same distance from the Sun, then they cannot both 
have the same speeds, since they travel in different orbits, and, in 
fact, it is the body in the larger orbit that has the greater speed at 
any given distance. Thus a comet with a period of 6 years may go 
out at aphelion to the neighbourhood of Jupiter, but Jupiter's 
orbit is the larger, and the planet will travel faster than the comet. 
Nevertheless, they both travel in the same direction, and will be 
neighbours in space over long intervals, since the speeds are com- 
paratively slow (about 5 miles per second for the comet, 8 miles 
per second for Jupiter). It is the prolonged influence of Jupiter 
under such conditions that causes such marked changes in 
cometary orbits. The attraction of the planet causes an accelera- 
tion, and this increases the velocity continuously; the increase in 
the speed forces the comet into a larger orbit. It may also be shown 
that the eccentricity is also changed by such an attraction in the 
forward direction (tangential to the orbit) ; and in the same way, 
forces in other directions will change the whole character of the 
orbit, altering its inclination or the direction of its major axis. Such 
effects are always present, however far away the comet may be, and 
they are particularly noticeable in those comets whose periods are 
about half that of Jupiter, because in such cases the comet may 
come within a short distance of Jupiter at each alternate revolu- 
tion. As an example, consider P/Pons-Winnecke, which has been 
seen at 15 returns and whose orbit is becoming noticeably larger 
and less eccentric. The original orbit of 1819 had a period of 5-6 
years, an inclination of 1 1 degrees, and a perihelion distance of 


0-77 a.u. Today the orbit has a period of 6-3 years, is inclined at 
22 degrees, and the perihelion distance is 1 -23 a.u. 

Effects of this kind can alter the orbit completely if the comet 
makes a really close approach to Jupiter. The word 'close' must be 
understood in the astronomical sense ; anything less than half a 
unit, (46 million miles) is really close. Thus Lexell's comet of 1770 
had a period of 5J years, but calculations showed that it had been 
very close to Jupiter to 1767 (actually within the orbits of the four 
big satellites). It made two revolutions about the Sun, (although 
only one was seen), and then again suffered severe perturbations, 
so that it was never seen again. The case of P/Brooks (2) is often 
quoted. This comet, first seen in 1889, had a period of about 7 
years, but this is the result of a close approach to Jupiter in 1886, 
before which the period was 29 years. 

We need not delve into the past to find further examples, for a 
very noticeable one is occurring at the present time with comet 
Oterma. Since 1942, when it was discovered by Miss L. Oterma, 
this comet has revolved about the Sun in its almost circular orbit 
within a period of 8 years, but it has been shown that before 1936 
the period was about 18 years. At the present time it is undergoing 
another of these protracted disturbances by Jupiter, lasting nearly 
two years, and approaching Jupiter to less than a tenth of a unit; 
as a result its period will be lengthened to about 19 years, while its 
distance from the Sun will be so greatly increased that it is doubtful 
if it will ever be seen again. 

It will be appreciated that the wide range of movement of a 
comet may entail a great deal of laborious calculation in making a 
prediction for the next return. The eccentric nature of a cometary 
orbit does not allow us to make many approximations, as is pos- 
sible with the planets. Planetary orbits are so nearly circular that 
the departure from the true circle introduces only minor complica- 
tions, and it is possible to express the position of the planet at any 
future time (allowing for all perturbations) by means of a series of 
equations, the numerical values of which can be arranged in a set 
of tables. The sums of the quantities taken from the tables will 
then give the position at the required date. But comets cannot be 






After Richter, 'Nature of Comets' 

dealt with in this way, and it is necessary to work out the effect of 
the disturbing planets in a step-by-step process. In this, the effect 
of each planet is worked out for a whole series of dates at equal 
intervals - perhaps 20 days. At each step the elements of the orbit 
will be slightly changed, and the new elements are then used for 
the next step. Thus if the period of the comet is 2,000 days (nearly 
6 years) there will be a hundred steps at this interval, for each of 
which the effect of all the planets is (or should be) calculated. It is 
not possible to state the details of the next return until all the steps 
have been completed - a long and arduous task. If the perturba- 
tions are not too heavy (which would entail reducing the interval, 
and using more steps), it is possible to do this work on an elec- 
tronic computer, but a really close approach to a major planet still 
remains a great difficulty. Methods of this kind are used regularly 


by members of the Computing Section of the British Astronomical 
Association, whose predictions every year have always been of the 
greatest value. These predictions do not aim at the highest 
accuracy (for example, perturbations by Jupiter and Saturn only 
may be considered, the other planets being ignored), but more 
detailed investigations are often published, particularly by com- 
puters in the U.S.S.R., Poland and Japan. The return of Halley's 
comet in 1986 is the subject of a long investigation by Dr Zadun- 
aisky, who is hoping to make use of electronic computers at the 
Massachusetts Institute of Technology. 

However careful this kind of work may be, it does not follow 
that the periodic comets are seen at each return. This is often due 
to the fact that the comet is unfavourably placed - too near the 
Sun, perhaps, or too far south to be above the horizon. But it must 
also be admitted that predictions are sometimes not as good as 
they might be, for unless the prediction, and its accompanying 
ephemeris, are quite close to the mark, it is impossible to find the 
comet in a large telescope, in which the field of view is always 
quite small. We find ourselves in a vicious circle - no observations 
(or poor ones) mean that the orbit cannot be adequately corrected ; 
a poor orbit means a poor prediction for the next return, and a 
poor prediction means no recovery. And so the comet becomes 
'lost' - but it is the astronomer who has lost the comet, and not the 
comet which has vanished. Several 'lost' comets have, in fact, been 
recovered, some as the results of more careful calculations, others 
by sheer chance. 

Nevertheless, comets must continuously shed their material, 
and this has been realized since the connexion of meteor showers 
with comets was established in the mid-nineteenth century. The 
great meteor showers of 1833 and 1866, in which the Leonids fell 
like snowflakes in the November sky, had already suggested the 
presence of an orbit for the meteoric dust, and at the end of 1866 
Schiaparelli showed that the August Perseid meteors move in the 
same orbit as the comet of 1862. Further examples followed in 
rapid succession: Leverrier and Peters proved the connexion 
between the November Leonids and Tempel's comet of 1866, 


while Weiss identified the Lyrids with the comet of 1861, and the 
Andromedids with Biela's comet. 

The behaviour of Biela's comet did much to convince astro- 
nomers that meteors could arise from the debris of comets. This 
faint comet was first seen by an Austrian officer, Wilhelm von 
Biela, at Josephstadt in Bohemia in 1826, and almost simultane- 
ously by Gambart at Marseilles. Both observers computed orbits, 
and showed that the comet was identical with the comets of 1772 
and 1805. The comet was seen again at its return in 1845, but at the 
end of that year it was seen to split into two parts. The two comets, 
travelling side by side about 160,000 miles apart, had no effect on 
each other at all, thus proving that their masses were quite small; 
each part displayed a short faint tail, and the brightness of the 
two seemed to vary, each alternately outshining the other. In 1852, 
under very unfavourable conditions, the double comet was again 
observed, but now the two nuclei were more than a million miles 
apart. Both vanished, and have never been seen again. The con- 
nexion between the Andromedids and Biela's comet having been 
demonstrated, each successive return of the comet to perihelion 
was awaited with interest, but it was not until 1 872 that any unusual 
display of meteors was noticed. On the night of November 27 in 
that year a really spectacular shower of meteors was seen, the 
shooting stars falling like a rain of fire, at the rate of several 
hundreds every minute. This was not, perhaps, so great a shower 
as those of the Leonids in 1833 and 1866, but it was impressive 
enough, and, to quote a writer of that period, 'it became evident 
that Biela's comet was shedding over us the pulverized products of 
its disintegration'. 

It is often stated, or implied, that Biela's comet gave rise to the 
Andromedid shower, yet these meteors from a point near the star 
Gamma Andromeda had fallen in considerable numbers in the 
years 1741, 1798 (before the comet was discovered), as well as in 
1830, 1838 and 1847. The same remark applies, with even more 
force, to the Leonids and Perseids, both showers having been 
recorded far back in history, and long before the associated comets 
were discovered. In more recent times, showers have been seen in 


association with comets Pons-Winnecke, and Giacobini-Zinner. 
The latter gave notable showers in 1933 and 1946, and its meteors, 
which come from a radiant in Draco, have been recorded by radar 
methods. This shower has recently been studied from the mathe- 
matical point of view, in an attempt to decide its possible origin. 
Calculations on the Mercury computer at Manchester University 
by J. G. Davies and W. Turski have shown that the most probable 
source of these Draconid meteors was an eruption of material from 
the head of the comet in 1894, the gas and dust leaving the head 
with quite small velocities - certainly less than 10 metres per 

We are still not clear as to the reason for such ejections of 
material from the head of a comet - they cannot possibly arise 
through perturbations - but if comets wear themselves out in this 
way, it is clear that they cannot be very ancient members of the 
solar system. Their origin can be guessed, for the attraction of 
Jupiter alone is sufficient to explain how these small orbits have 
been derived from larger ones by continuous perturbations by the 
giant planet. The question then arises as to how often the comet 
can return to the perihelion, constantly shedding its material, 
before it is finally worn out. We might make a guess that some 
hundreds of revolutions - some thousands of years - are needed to 
deplete a comet of all its gases and fine dust. Yet that is an insig- 
nificant amount of time in the astronomical sense. We need to 
know a great deal more about these interesting objects before we 
can begin to solve all the problems they present. There are already 
plans afoot to send a space probe out to a convenient comet to 
make closer measurements, or even to pass through the luminous 
coma which surrounds the nucleus. In a public lecture in 1958, the 
late Otto Struve said : 

As an astrophysicist I would like to make a satellite provided 
with an explosive charge blow up the solid icy nucleus of a 
comet. ... It would be quite interesting to see what would 
happen if the entire one-mile nucleus of the comet were sud- 
denly converted into vapour. Since the solar system contains 


approximately one hundred billion comets we need not be 
afraid that we shall run out of comets if we sacrifice one or 
several for such an experiment. 

It is comforting to think that the present plans are much less 
drastic! The enormous difficulties are fully realized, and perhaps 
the greatest of these is to select a suitable comet, one which is 
bright enough to be observed, big enough to be worth investigat- 
ing, and adequately observed over many revolutions, so that its 
orbit and its position in space are known with high accuracy. And 
there are very few comets which can be said to come up to these 
high standards ! 

Recent Advances in Astronomy 


Each year brings its new quota of 'space research successes', and 
1963 has been no exception. There was, for instance, the flight 
of Gordon Cooper, the U.S. astronaut, which was carried through 
without the slightest hitch, and which showed that the Americans 
have made remarkable progress since the days when they were 
hard pressed to launch even a small unmanned satellite. From 
Russia came two more spectacular Vostoks, one piloted by 
Valery Bykovsky and the other by the first woman in space, 
Valentina Tereshkova. The Russians were in orbit at the same 
time, and Bykovsky stayed aloft for longer than any astronaut 
before him. 

There has been much discussion as to why the Russians selected 
a woman pilot. In some quarters, the choice was even described 
as a 'publicity stunt'. To me, at least, this seems ungenerous, and 
it surely is more likely that Valentina Tereshkova was chosen 
simply because she happened to be the most suitable person for 
that particular mission. In any case, she more than justified her 

But though the Russians have achieved so much, they have 
also had their failures, and two of their latest unmanned probes 
have certainly not done all that had been hoped of them. 

After the successful photography of the reverse side of the 
Moon, in 1959, it was generally thought that further Soviet 
lunar probes would follow. Yet for some years, they did not; it 
was not until 1963 April 2 that Lunik IV followed in the wake of 
its predecessors. According to Russian statements, it had a 
weight of lj tons, and was crammed with complex instrumen- 


As usual, prior information was scanty, and even when Lunik 
IV was on its way there was no certain indication of what it was 
meant to do. The most reasonable answer was that the probe 
was intended to make a 'soft landing' on the Moon's surface - 
or, alternatively, to drop a package on to the Moon, so providing 
an automatic lunar laboratory. It also seemed that the Russians 
might try to transmit television pictures of the Moon from close 
range, as the Americans had attempted to do with the so far 
unsuccessful Ranger rockets. 

World attention was focused on Lunik IV as it sped toward the 
Moon, but the outcome was in the nature of an anti-climax. There 
was no landing, and presumably no television pictures. The 
rocket simply passed by the Moon at a distance of several thou- 
sands of miles, and went off into space, just as Lunik I had done 
more than four years earlier. The obvious suggestion is that the 
Russians were unable to guide it down on to the Moon, or to effect 
a separation between the hypothetical 'landing package' and the 
probe itself. This is as much as can be said at the moment, and at 
the time of writing (July 1963) no further word has come from 

The case of the Soviet probe Mars /was different, since here the 
launching was carried through faultlessly - on 1962 November 1 
- and the vehicle sent back information which was of great value. 
Measures of cosmic radiation, for instance, were received, 
together with information about the so-called 'solar wind' and 
the magnetic fields in space. The ultimate aim of the experiment, 
to send the probe close to Mars and obtain new data about the 
Martian surface and atmosphere, was not, however, achieved. 
Troubles developed, and when the probe had receded to a dis- 
tance of rather more than sixty million miles from Earth all 
contact with it was lost. 

This relative failure merely serves to stress the magnitude of 
the American triumph with their Venus probe, Mariner 2. 
Launched in August 1962, the Mariner passed within 22,000 
miles of Venus on December 14 of the same year. Its instrumen- 
tation functioned excellently, but when the results were analyzed 


they proved to be extremely unexpected. When the Mariner 
findings were announced, early in 1963, it became clear that many 
of our previous ideas about Venus as a world would have to be 
drastically revised. 

In an article entitled 'The Surface of Venus', published in the 
1963 Yearbook, I described various theories about the planet. 
Since we can never see the surface, which is permanently hidden 
by the opaque atmosphere, direct information was lacking, but 
there were two possible pictures of Venus as a world. Either it 
was a fiercely hot dust-desert, with a surface temperature high 
enough to rule out advanced life-forms of the type we know, or 
else the planet was largely covered with water, in which case it 
might well support primitive marine organisms of the sort which 
flourished on Earth during the Cambrian Period. My own incli- 
nation was to prefer the marine theory, but in the article I did add 
that 'further research may show that the desert picture is right, 
after all . . . if we are to find out what the planet is really like, 
we must pin our faith in space research methods'. 

One of the primary objectives of the Mariner flight was to 
obtain measures of the surface temperature of Venus. These and 
other details of the Mariner programme are described in the 
article by Howard Miles; suffice to say here that if the announced 
value (+800 degrees F.) is of the right order, we must assume that 
Venus is a world quite unsuited to live as we know it. Yet at any 
rate, Mariner 2 has represented one of the major triumphs of the 
early days of practical space research. 

Meanwhile, it seems that our first space-target following 
successful landings on the Moon is likely to be not Venus, but 
Mars; and the Red Planet itself came under study by the Ameri- 
cans - not by means of a rocket probe, but with instruments 
carried to 80,000 feet in a large balloon, Stratoscope II. (Strato- 
scope I, designed for solar research, had made a successful ascent 
some years before.) It may seem rather curious to leave rocketry 
and come back to that age-old flying machine, the balloon, but in 
fact balloons are in many ways more suitable than rockets for 
carrying out spectrographic work on the planets; they cannot 


reach cosmic heights, but they can at least pass beyond most of 
the Earth's atmosphere, which for this purpose is quite good 
enough. The instruments are recoverable, which is a vitally 
important factor. In this new experiment, the main attention was 
focused upon the Martian atmosphere, and although the full 
results have not yet (July 1963) been published, it has been stated 
that five complete scans of the planet were made in infra-red, 
revealing definite traces of water-vapour. Mars, too, was badly 
placed through the rest of 1963, and will not return to opposition 
until March 1965, but at least an encouraging start has been made. 

Before leaving the planets, mention should be made of an 
interesting if unspectacular visitor - the pygmy asteroid Betulia, 
which passed by the Earth on 1963 May 21 at a distance of only 
14,600,000 miles. It never exceeded the ninth magnitude, so that a 
telescope was needed to show it, but it nevertheless attracted a 
certain amount of attention in astronomical circles. 

Most of the asteroids move round the Sun in orbits between 
those of Mars and Jupiter. A few have eccentric paths which may 
bring them relatively close to the Earth; of this group the most 
celebrated is Eros, discovered by Witt in 1898, and which made 
an approach in 1931 which was used to make a new determination 
of the astronomical unit. Because an asteroid looks exactly like a 
star, its position may be determined very accurately by photo- 
graphic methods, and its orbit may be calculated with great 
precision; this, in turn, leads to a measure for the astronomical 
unit. The work on Eros was analyzed by H. (afterwards Sir 
Harold) Spencer Jones, who finally announced a value for the 
astronomical unit of slightly over 93,000,000 miles. 

This figure has now been superseded, since new methods, based 
upon radar, have been developed. Consequently, there was no 
international programme to make use of Betulia in the same way, 
though a great many photographs were taken and will later be 
analyzed. Studies of different type were carried out at the Flag- 
staff Observatory, in Arizona, by Elizabeth Roemer and E.J. Opik, 
who wanted to see whether Betulia was a genuine asteroid or 
whether it was in fact a comet. There are a few asteroids, notably 


Hidalgo (No. 944) whose orbits are highly eccentric, and decidedly 
cometary; Hidalgo itself travels almost from the path of Venus 
out to a distance comparable with that of remote Saturn. It had 
been suggested that Betulia, Hidalgo and others might, if carefully 
studied, show traces of comet-like tails. However, Roemer and 
Opik failed to detect anything of the sort; under all conditions 
Betulia still appeared star-like, and it seems that we must regard 
these curious bodies as bona-fide members of the asteroid swarm. 

So far as comets were concerned, 1963 was not expected to be 
an eventful year, though the usual faint periodical comets arrived 
upon schedule. A brighter, non-periodical comet was discovered 
in the spring by the Japanese astronomer Ikeya, and became 
clearly visible to the naked eye; but when at its best it lay well 
south of the celestial equator, and European and United States 
observers never saw it to advantage. By the law of averages, a 
'great' comet is now surely overdue; the last appeared as long 
ago as 1910, whereas during the last century spectacular visitors 
appeared quite frequently. We may hope for at least one more 
brilliant comet before Halley's Comet comes back again in 1986. 

In the field of stellar astronomy, perhaps the most interesting 
discovery of 1963 was announced by Dr van de Kamp and his 
colleagues in the United States. This concerned the faint object 
known as Barnard's Star, which van de Kamp and bis team have 
found to be attended by an invisible body with a mass only 1| 
times that of Jupiter - in which case it must be a planet, and not 
simply a very dim star. 

Barnard's Star is only six light-years away, so that it is our 
nearest stellar neighbour with the exception of the three com- 
ponents of the Alpha Centauri system. Its position (epoch 1950) 
is R.A. 17h 55m, dec. + 4° 33', which places it in the constellation 
of Ophiuchus; it is of magnitude 9-6, so that it is a comparatively 
bright telescopic object. It is, of course, a feeble Red Dwarf. It 
has been nicknamed the 'Runaway Star' because its annual 
proper motion amounts to 10"«30, which is easily a record; the 
annual proper motion of Sirius, for instance, amounts to less 
than li". 


Van de Kamp and his colleagues have spent many years in 
studying the motion of Barnard's Star, and have now found that 
this motion is not quite regular; there is evidence of perturbation 
by a much less massive body. Investigations of this sort are by no 
means new, and it is worth remembering that the faint companion 
of Sirius was predicted theoretically, by F. W. Bessel, long before 
Clark first saw it in 1862. Much more recently, 61 Cygni B has 
been found to be attended by an invisible lightweight companion, 
as was announced by K. Strand in 1944, and there are a few other 

The real importance of Van de Kamp's discovery is that the 
companion of Barnard's Star is of such remarkably low mass. A 
body equal to only 1| times the mass of Jupiter cannot possibly be 
a star, and it seems that for the first time we have positive evidence 
of an 'extra-solar' planet. The companion of 61 Cygni B is said 
to be at least 15 times as massive as Jupiter, so that we cannot be 
certain of its nature. 

The results with Barnard's Star seem to be conclusive, but 
they will not easily be repeated elsewhere, since there are few 
stars of comparable distance and none with as rapid a proper 
motion. Meanwhile, our ideas as to the origin of our own Solar 
System are bound to be affected. The Sun's family cannot be in 
the nature of a cosmical freak - it would be too much of a coin- 
cidence to expect two such freaks, and probably more, in the very 
limited part of the Galaxy available for detailed study. Systems 
of planets are probably very common, and this in turn increases 
the probability of the widespread occurrence of life in our own 
and in external galaxies. 

Another interesting event of 1963 was the discovery of a naked- 
eye nova near the brilliant Vega. It was detected by the Swedish 
amateur Dahlgren, using a pair of binoculars, and found inde- 
pendently at about the same time by L. Peltier in the United 
States. It lay so near the border between Lyra and Hercules that 
there was some discussion as to which constellation should claim 
it; eventually the International Astronomical Union pronounced 
in favour of Hercules. It reached the third magnitude, so that it 


was the brightest nova for some time. Excluding Nova Argus 
1942, which was extremely difficult to see in Britain and the 
northern United States because of its southerly declination, only 
two more brilliant novae have appeared during the past thirty 
years, one in Hercules (1934) and the other in Lacerta (1936). 

Nova Herculis 1963 proved to be of the slow type, and its 
fading was relatively gradual, so that it did not remain a naked- 
eye object for very long. It was, of course, carefully studied from 
observatories all over the northern hemisphere, and useful results 
were obtained. At the end of the summer of 1963 it was still easy 
to see with a moderate telescope. 

One of the most unhappy events of 1963 was the sudden and 
quite unexpected death of a great astronomer - Otto Struve, one 
of the famous family whose first famous representative was 
F. G. W. Struve, of double star fame. Though of Russian descent, 
Otto Struve lived and worked in the United States. He made out- 
standing contributions to astronomical research, particularly in 
the field of astrophysics, and was also a very skilful writer of 
'popular' books, one of which appeared not long before his 
death. He will be greatly missed by his friends and colleagues all 
over the world. 

When we look back at 1963, we may claim that in many ways 
it was an important year astronomically. No doubt there will be 
further developments in 1964, though it may be too much to hope 
that we shall be treated to the spectacle of a brilliant nova, or 
even a great comet stretching its tail across the heavens. 

Some Recommended Books 


Larousse Encyclopedia of Astronomy, by L. Rudaux and G. de 
Vaucouleurs. (Batchworth, 1959; 63s.) 
Not an encyclopedia, but a detailed account of astronomy 
for beginners ; 500 pages, and more than 800 diagrams and 
plates. Value for money. 

Astronomy, by Robert H. Baker, (van Nostrand, 1959; $6.95.) 
A standard textbook, which has now reached its 7th 

Atlas of the Universe, by B. Ernst and T. E. de Vries. (Nelson, 
1961; 42s.) A detailed and profusely illustrated encyclo- 
paedia of astronomy. 

The Young Astronomer, by E. A. Beet. (Nelson, 1962; 7s. 6d.) 
An outstandingly good, clear introduction to astronomy, 
written for school-age readers by the President of the British 
Astronomical Association. 

Astronomy, by Fred Hoyle. (Macdonald, 1962; 635.) A fine 
book, lavishly illustrated; concerned mainly with the 
development of modern astronomy through the application 
of the laws of physics. 

Astronomy, by Patrick Moore. (Oldbourne, 1961 ; 355.) A book 
telling the story of the development of astronomy; it has 
many coloured photographs and drawings. 

The Fascinating World of Astronomy, by R. S. Richardson. 
(Faber & Faber, 1962; 25s.) A popular book in 'question 
and answer' form, written by an American astronomer who 
is as famous for his general books as for his own very 
considerable contributions to the science. 


Measuring the Universe, by Henry Brinton. (Methuen : Outline 
series, 1962; 9s. 6d.) A logical, concise account. 

Lectures and Essays: 

The Exploration of Outer Space, by Sir Bernard Lovell. (Oxford 
University Press, 1962 ; 16s.) A book based on the Gregynog 
Lectures of October 1961 ; it deals with subjects ranging 
from radio astronomy to the possibility of life elsewhere in 
the universe. Non-mathematical, and so may be followed 
by the beginner in astronomy, though it will be of equal 
value to the serious worker. 

Radio Astronomy: 

Radio Astronomy, by F. Graham Smith. (Penguin, 1960; 

Is. 6d.) An excellent account by one of the Cambridge 

Radio Studies of the Universe, by R. D. Davies and H. P. 

Palmer. (Routledge & Kegan Paul, 1959; 25s.) Two 

members of the Jodrell Bank team explain their work. 

Radio Astronomy for Amateurs, by F. W. Hyde. (Lutterworth, 
1962; 25s.) F. H. Hyde uses the only full-scale amateur 
radio astronomy observatory in Britain, and collaborates 
extensively with American professional research workers. 
In this book he gives details of his equipment and methods. 
Invaluable for any amateur seriously interested in the 

The Solar System: 

The Planet Jupiter, by B. M. Peek. (Faber & Faber, 1958; 
42s.) The only detailed account - and an excellent one - of 
this great planet. 

The Sun and the Amateur Astronomer, by W. M. Baxter. (Lutter- 
worth, 1963; 25s. A book by a well-known amateur 
observer of the Sun, describing the methods used in this 
work and the results obtainable by the skilful amateur. 
Illustrated with many excellent photographs. 


The Planet Mercury, by Werner Sandner. (Faber & Faber, 
1963, 2\s.) A non-technical account of what is known about 
Mercury, translated from the German by A. L. Helm. 

Mars, by Earl C. Slipher. (Sky Publishing Corporation, Cam- 
bridge, Mass.) An elaborate book, containing a description 
of Mars and numbers of magnificent photographs, taken 
mainly at Flagstaff. The author has had many years' ex- 
perience, and has probably paid more attention to Mars than 
any other astronomer of modern times. 

The Measure of the Moon, by R. B. Baldwin. (University of 
Chicago Press, 1963; 97s.) A large, well-produced book. 
Much of it deals with the author's interpretation of the 
lunar craters as being due to meteoric impact, but there is 
also much general information, and extensive references. 
Very strongly recommended to all those who are in any way 
interested in the Moon. 

Survey of the Moon, by Patrick Moore. (Eyre & Spottiswoode, 
1963; 25s.) An account of modern selenography, including 
a map of the Moon in sixteen sections. 

The Moon - a Russian View. Edited by A. V. Markov. (Uni- 
versity of Chicago Press, 60s.) A valuable collection of 
lunar papers by distinguished Soviet astronomers. 

The Sun's Family, by James Muirden. (Weidenfeld & Nicolson, 
1962; 9s. 6d.) An account of the Solar System, written 
specifically for readers of school age, but also suitable for 
adult beginners in astronomy. 

The Planet Saturn, by A. F. O'D. Alexander. (Faber & Faber, 
1962; 63j.) A comprehensive account of Saturn - the first 
book dealing with this planet to be published for nearly a 
century. It is indispensable to any student of Saturn, and 
must remain the standard work. 


The System of Minor Planets, by Giinter D. Roth. (Faber & 
Faber, 1962; 25j.) Translated from the German by A. L. 
Helm. The only recent book to deal exclusively with the 

Space Research: 

Satellites and Scientific Research, by D. King-Hele. (Routledge 
& Kegan Paul, 1962; 25s.) One of the best accounts so far 
of the behaviour and uses of artificial satellites. 

Space Laboratories, by G. Zhdanov and I. Tindo. (Foreign 
Languages Publishing House, Moscow; in English, distri- 
buted by Central Books; 1962, 6s.) A useful account of the 
research carried out by satellites and space probes. 

Artificial Satellites, by G. V. E. Thompson. (Weidenfeld & 
Nicolson, 1962; 9s. 6d.) A popular description of the present 
satellite programme. 

Express to the Stars, by Homer E. Newell. (Hutchinson, 1962; 
25s.) A detailed and authoritative account of the American 
space programme, and of the application of rocketry in 
general. The author is the Director of the Office of Space 


Changing Views of the Universe, by Colin A. Ronan. (Eyre & 
Spottiswoode, 1960; \5s.) A study of the historical back- 
Astronomical Photography, by G. de Vaucouleurs. (Faber & 
Faber, 1961 ; 25s.) An historical account of the development 
of astronomical photography, from its earliest days up to the 
present time. 
Physics of Interstellar Space, by S. Pikelner. (Foreign Languages 
Publishing House, Moscow, 1962; in English, 6s.) Semi- 
technical and highly informative. 

Life in the Universe, by Francis L. Jackson and Patrick Moore. 
(Routledge & Kegan Paul, 1962; ISs.) A discussion of the 


problem written jointly by a research bacteriologist and an 
Celestial Objects for Common Telescopes, by the Rev. E. W. 
Webb. (Dover Books.) A re-issue of Webb's classic book. 
Some of the plates have been replaced, but, unfortunately, no 
attempt has been made to bring the text up to date. Never- 
theless, the book remains the best of its kind. 

Astronomical Societies 

The advantages of joining an astronomical society are obvious, 
and this is a step which should be taken by any amateur who is 
even moderately interested in the subject. The leading society in 
Britain is of course the Royal Astronomical Society (Burlington 
House, Piccadilly, London, W.l) which is a professional organiza- 
tion, though there are many Fellows who are amateurs. The leading 
amateur society is the British Astronomical Association: secre- 
tarial address 303 Bath Road, Hounslow West, Middlesex. 
Meetings are held on the last Wednesday of each month (except 
July, August and September) at Burlington House, at 5 p.m. The 
annual subscription is 45s. ; for a member 25 years of age or less 
on his last birthday preceding 1 August, the subscription is 30s. 
Special sections are devoted to the Sun, Moon, Mercury and 
Venus, Mars, Jupiter, Saturn, comets, meteors, variable stars, and 
aurorae and the Zodiacal Light ; there is also an Historical Section, 
and a section dealing with instruments and observing methods. 
The B.A.A., founded in 1890, has a distinguished observing record. 
Publications include a regular Journal and annual Handbook. 

For young enthusiasts there is the Junior Astronomical Society 
(secretarial address, 44 Cedar Way, Basingstoke, Hampshire) 
which caters mainly, though not exclusively, for those of school 
age. Meetings in London are held quarterly at Caxton Hall, near 
Victoria. The journal, Hermes, is issued quarterly. The annual 
subscription is 10s. There are various branches which organize 
their own programmes: at Croydon (J. H. Lytheer, 1 Temple 
Avenue, Shirley, Croydon, Surrey); Leeds (D. Fry, 5 Belle Vue 
Terrace, Belle Vue Road, Leeds 3); Golders Green (Miss L. 
Morrison, 49 Booth Road, Colindale, London, N.W.9); and 
Glasgow (D. McDougall, 1444 Gallowgate, Parkhead Cross, 



Glasgow El). Other branches are in the process of formation. 
Inquiries should in the first instance be sent to the Society's 
Secretary, E. W. Turner. 

Many towns have their own local astronomical societies. 
Among these are : 


Secretarial Address 


- Annual 

Meetings Re- 

Astronomy Group 

17 Hannafore Road, 
Birmingham 16 
(W. E. Marsh) 


10s {5s Tor 
under 21) 

Monthly, Oct-May at 1 
Midland Institute, 
Paradise Street, 

Bristol Astronomical 

12 Lambley Road, 
Bristol 5 
(S. J. Williams) 


1 guinea 
(10 5 6d 
for those 
under 16) 

(6s for 
under 21) 

Monthly, Sept-May, 
at Royal Fort, 
University of Bristol 

Chester Society of 
Natural Science: 
Dept. of Astronomy 

15 Sheldon Avenue, 
(Miss N. Thomas) 


Grosvenor Museum, 2 
Grosvenor Street, 

Chesterfield 10 George Street, 
Astronomical Society Brimington, 



The Barnett 3 

Crayford Manor House 
Astronomical Society Centre, Crayford 



Weekly at 4 
Manor House 

Crewe Astronomical 

465 Crewe Road, 
Wistaston, Crewe, 



Crewe County 
Grammar School, 
Ruskin Road, 

Cumberland and 20 Fernleigh Drive, Seaton, 

Westmorland Workington, 

Astronomical Society Cumberland, 
(W. L. Rae) 

Astronomical Society 

of Edinburgh 
Fellowship of Junior 



Leeds Astronomical 

126 West Savile Terrace, 130 

Edinburgh 9 
58 Ogilvie Terrace, 30 

Edinburgh 1 1 

20s CaltonHill 


ls6d CaltonHill 


The University, Leeds 120 10s 

Leeds University, 
2nd Wednesday of 
each month, 

Leicester Astronomical 49 Bringhurst Road, 60 

Society Leicester 

(C. Shuttlewood) 

Lincoln Astronomical Oak Crescent, Cherry 80 
Society Willingham, Lincoln 

(P. Hammerton) 
Liverpool 135 St Michael's Road, 200 

Astronomical Great Crosby, 

Society Liverpool 23 

(J. E. Abrahams) 

Manchester University Dept. of Astronomy, 85 

Astronomical Society The University, 
Manchester 13 

1 guinea 

Leicester Museum 

(10s for 

and Art Gallery 

those aged 

16-18; 5s 

for those 

under 16) 

10s senior 

Lincoln Y.M.C.A. 

5s junior 


Royal Institution, 

(As for 

Colquitt Street, 



under 21) 


The University 




Secretarial Address Member- Annual 
ship Subscrip- 





Nottingham Astro- 
nomical Society 


facing Craig Avenue, 
Summerseat, Bury 

30 Kew Gardens, 
Whitley Bay, 

61 Abbey Road, 
Beeston, Notts 
(Miss M. Mott) 

Norwich Astronomical 68 Clarendon Road, 
Society Norwich 

(W. E. Bennett) 

Swansea Astronomical 77 Graiglwyd Road, 
Society Cockett, 

(R. E. Roberts) 



York Astronomical 

Preston and District 


Clennon Park, 
Paignton, Devon 
(Mrs A. Longman) 

9 Tallants Road, 
Bell Green, 
(A. Hancocks) 

27 Garden Flat Lane, 
Dunnington, York 


51 Bispham Road, 
Carleton, Poulton- 
le-Fylde, Lanes 
(C. Lynch) 

Hull and East Riding Rosedene. Flinton, 
Astronomical Society Sproatley, nr Hull 


61 Bushbury Lane, 
(M. Astley) 

150 £1 Godlee Observatory 1 1 

(seniors) Manchester College of 

10$ Technology, 

(juniors) Sackville Street, 
Manchester, 1 

64 15s King's College, 

(students Newcastle 
Is 6d) 

30 1 guinea 


Nottingham Mechanics 12 
Institute; first 
Thursday in each 


under 17) 

25 1 guinea 

30 ISs 

Assembly House, 
Norwich, and the 

Royal Institution 
of South Wales, 



R.A.F. Training Centre 
Newton Abbot, 
Devon; third 
Thursday of each 

25 £4 20 Humber Road, 15 

(£2 for Stoke, Coventry 

those age 

30 £1 York Educational 16 

(students 5s) Settlement 

30 15s 





pupils 5s) 

1 5s (5s 
to ladies 
and those 
under 18) 

Chamber of 17 

49a Fishergate, 

3rd Monday of each 
month, Sept.-May 
inclusive, 19.30 h. 

Kingston High 18 

School, Hull 

Committee Room, 19 

38 Tettenhall Road, 
7.40 pm, alternate 
Mondays, Sept.-April 


1. The Group has a 12 in. reflector in an observatory at 
Birmingham, and a 21 in. is under construction. General meetings 
are held once a month from October to May, with lectures and 
film shows. The Construction Section meets weekly throughout 
the year. The Group runs a lending library, an observing section, 
and a junior section. 


2. From January to May a course of lectures is held in con- 
junction with the Liverpool University extra-mural department, 
on subjects allied to astronomy. Open to non-members of the 
Society. Fee Is. 6d. 

3. The Observatory has an 18 in. Newtonian reflector and 
also a lecture room. 

4. Members who have satisfied the Committee as to their com- 
petence may use the 12 in. reflector in the H. P. Wilkins Memorial 

5. Facilities are available to members at the Observatory, 
Calton Hill. Small telescopes are also loaned to members of the 
Observing Sections. Members meet on Fridays throughout the 
year at the Observatory. Library, and a collection of lantern slides. 
Monthly star maps and astronomy notes are issued to all members. 

6. There are observing nights at the Observatory, Calton Hill. 
Monthly notes are issued to members. Some small telescopes are 
loaned to members. Training is given in observing techniques. 
There is a small library. 

7. The Observatory, with a 15 in. reflector, will be completed 
in 1962. 

8. An observatory and lecture room are now being built. 

9. The Society, founded in 1881, has a strong junior section, a 
radio physics section, a library and a collection of lantern slides. 
Telescopes are available for borrowing by members, and the 
Society's 5 in. Cooke equatorial is available to members at a 
weekly meeting held at the Society's Observatory, Central Tech- 
nical College, Byrom Street, Liverpool. 

1 0. The Society has the use of the Godlee Observatory, operated 
by the Manchester Astronomical Society. The Society also has 
facilities for producing telescope objectives, etc. 

11. The Society's 12 in. and 8 in. reflectors are available two 
nights per week at least. Winter session lectures are held in the 
Reynolds Hall of the College. 

12. The 8-5 in. Society reflector is kept by the Director of 
Observing, A. W. Lane Hall. 

13. The Society has its own observatory, with a 10 in. reflector, 


and adjoining club-room, off Newmarket Road, Norwich. This is 
available to members at any time by arrangement. Regular 
evenings are Tuesdays, Wednesdays, and Saturdays. 

14. The Swansea Observatory has a 9 in. Newtonian reflector, 
and photographic equipment. 

15. Workshops contain grinding and polishing facilities. The 
Library and Club Room, available seven days a week, are available 
to all members. There is a monthly magazine, Cosmos. 

16. Meetings are held at 7.30 on the second Thursday of each 

17. The observational work of the Society is carried out at the 
Jeremiah Horrocks Observatory, Moor Park, Preston, on Monday 

18. The observatory at Kingston High School, Hull - equipped 
with a 4-inch refractor - is available for use by arrangement. 
Meetings are held in the second Friday of each month from 
October to April inclusive. 

19. Library facilities are available. 

This list of societies may not be complete. The secretaries of any 
societies not included are invited to send details to Patrick Moore, 
c/o Eyre & Spottiswoode Ltd., 22 Henrietta Street, London WC2, 
for inclusion in the 1965 Yearbook; any alterations of details given 
for societies listed here should also be sent, so that the list may be 
kept fully up to date. 

Glossary of Astronomical Terms 

aberration — (1) the distortion of an image in an imperfect optical 
system; (2) the apparent displacement of a star from its true 
position owing to the finite velocity of light. It includes (a) the 
effect of light-time, the object being seen where it was when 
light left it; this effect is ignored in dealing with stars, since 
the light-time is not known; (Z>) the effect of the Earth's motion, 
which, combined with the velocity of light, causes an apparent 
displacement of the object. This effect is called stellar aberra- 
tion, and the combination of the two effects is planetary aber- 

absorption lines — dark lines in a continuous spectrum caused by 
absorption of light of certain wave-lengths by a layer of gas 
(e.g., an atmosphere) cooler than the source of light. 

albedo — ('whiteness') — the ratio of the amount of sunlight re- 
flected from a planet or satellite to the amount received. The 
Moon reflects only 7 per cent of the sunlight falling on it; its 
albedo is therefore 0.07. 

altitude — the angular distance of a body above the true horizon; 
the nature of the visible horizon will affect the apparent 

angstrom unit — the unit of wave-length in measurements of light, 
X-rays, etc. Symbol a; it is one hundred-millionth part of a 
centimetre, or a ten-thousandth part of a micron. The whole 
of visible light is contained in the range from 3,900a (violet) to 
7,500 a (red). 

aphelion — that point in an (elliptical) orbit of a planet or comet 
which is farthest from the Sun. 


apogee — that point in the orbit of the Moon, or of an artificial 
satellite, which is farthest from the centre of the Earth. 

apparent place — the observed position of a star or planet, as 
distinct from the mean place. 

apparent solar time — time measured by the hour angle of the true 
Sun; the time measured by a sundial. The difference apparent 
time minus mean time is the equation of time, and this may 
amount to more than 16 minutes in November. 

appulse — a very close conjunction of two planets, or of a planet 
and a star. 

apse line, or line of apsides — the line in an orbit which joins the 
nearest and farthest points from the central body; in an un- 
perturbed ellipse it corresponds to the major axis. 

asteroids — see minor planets. 

Astronomical Ephemeris — the modern name (since 1960) of the 
British Nautical Almanac, which was first published in 1767; it 
is identical in content with the American Ephemeris. 

astronomical unit — the mean distance of the Earth from the Sun; 
the semi-major axis of the Earth's orbit. May be taken as 
93 million miles. 

astrophysics — the branch of astronomy which uses the laws of 
physics to study the constitution and evolution of the stars. 

az muth— the angular bearing of an object measured round the 
horizon from north or south points. In astronomy it is now 
usual to measure the azimuth from the north round through 
east, south and west, from 0° to 360°. 

binary — a double star in which the two components are physically 
connected, revolving about their common centre of mass under 
the influence of the mutual gravitational forces. Probably one 
star in every two or three is a binary. 

celestial sphere — an imaginary sphere of infinite radius, centred at 
the observer, on which the stars and planets appear to be fixed. 


Their positions may then be referred to fixed great circles (such 

as the equator or ecliptic) on the sphere. 
cepheid—a. variable star characterized by a rapid rise to maximum 

brightness, followed by a slower and less regular decline; 

named after the typical star Delta Cephei. The periods range 

from 1 to 45 days, and the period is in all cases proportional 

to the absolute brightness, from which distances can be 

chromosphere — the lower layer of the Sun's atmosphere, red in 

colour, and consisting mainly of hydrogen; it extends for some 

thousands of miles, while prominences rise from it to much 

greater distances. 
circumpolar stars — stars which do not rise or set, but merely circle 

the pole; all stars whose declinations are greater than the 

colatitude of the observer are circumpolar. 
cluster variables — short period variable stars first detected in 

globular clusters, and having periods less than one day. 

clusters — groups of stars having a common motion through 
space. The main groups are (1) open clusters within the Galaxy 
containing at most a few hundred stars with dust and gas 
clouds; (2) globular clusters of a symmetrical shape, contain- 
ing many thousands of stars including short-period variables 
and Population II stars. They are distributed uniformly at great 
distances round the centre of the Galaxy. 

colatitude — the complement of the latitude; 90° minus the latitude. 

The meridian altitude of the equator at any place is equal to 

the colatitude. 
colour index — the difference between the photographic and visual 

magnitudes of a star; from this value the effective temperature 

may be deduced. 
comes — the fainter component of a double star. 
conjunction — the nearest apparent approach of two celestial 

objects, when one appears to pass the other ; usually considered 

to occur when they have the same longitude. 


Inferior conjunction of Mercury and Venus occurs when the 
planet is between the Sun and the Earth. 
Superior conjunction of any planet occurs when it is on the 
farther side of its orbit, the Sun lying between planet and Earth. 

continuous creation — the theory that matter is being continuously 
created throughout the universe, to replace losses caused by 
the recession of the galaxies. This is the steady-state theory, 
and it implies that the universe had no beginning and will have 
no end ; creation is confined to individual systems. 

corona {solar) — a pearly-white halo of light surrounding the Sun; 

this is the outer layer of the Sun's atmosphere, and can be 

traced to great distances from the Sun, joining up with the 

zodiacal light. 
cosmic radiation — highly penetrating radiation which reaches the 

Earth from outer space; it consists of electrically charged 

particles of high energy. 

cosmogony — the science which deals with the origin of the uni- 
verse, or of our Galaxy or the solar system. 

cosmology — the study of the universe as a whole, its nature in 
space and time, and the relations between its various parts. 

cusps — the horns of the moon or of an inferior planet when in the 
crescent phase. 

D-layer — the lowest ionized layer in the Earth's atmosphere; it is 
about 50-60 miles above the Earth, and disappears almost 
completely at night. 

clay — the period of the Earth's rotation. It may be measured with 
respect to the stars {sidereal day), the true sun {apparent solar 
day) or the mean sun {mean solar day). See apparent solar time, 
Greenwich Mean Time, mean solar time, sidereal day. 

declination — the angular distance of a celestial object north (+) or 
south (—) of the celestial equator. 

dew cap — an open tube fitted to a refractor, extending the tele- 
scope tube beyond the objective; it prevents condensation on 
the front surface of the lens. 


diffraction rings — the image of a star in a telescope is not a point, 
but has a definite size; this 'spurious disc' is surrounded by a 
number of diffraction rings. These are caused by the spreading 
of light (which is a wave-motion) round the edges of an obstacle 
— in this case, the aperture of the telescope — to give alternate 
light and dark bands called diffraction fringes. If the aperture 
of the telescope is increased, the spurious disc becomes smaller, 
and the diffraction rings less conspicuous. 

Doppler effect — the apparent change of wave-length in any form 
of wave-motion (sound, light, radio, etc.) caused by the motion 
of the observer or of the source, or both. The change is pro- 
portional to the velocity. 

double stars — two stars which appear close together in the sky, 
either because they are physically connected (see binary) or 
because they chance to be almost in line, though at different 
distances (optical double). 

dwarf stars — the stars of the main sequence; the giant stars are 
more luminous, and the white dwarfs less luminous, than the 
stars of the main sequence. 

eclipse — an eclipse of the Moon (or any other satellite) occurs 
when it passes into the shadow of the planet; such an eclipse 
may bepenurnbralif the satellite does not enter the umbra of the 
shadow, or partial or total. An eclipse of the Sun occurs when 
the Moon passes between the observer and the Sun; in this 
case the eclipse may be partial, annular (ring-like, if the Moon 
does not entirely cover the Sun's surface) or total. An eclipse 
of the Sun can only occur at New Moon, and an eclipse of the 
Moon only at Full Moon. 

ecliptic — the great circle on the celestial sphere which marks the 
apparent path of the Sun. It is the projection of the Earth's 
orbit on the celestial sphere. 

elongation — the apparent angular distance of a planet from the 
Sun, or of a satellite from the parent planet, etc. 

emission lines — bright lines in a spectrum due to the emission of 
light from a glowing gas at low pressure. 


ephemeris — a table of positions of the Sun, Moon, planets, 
comets, etc., for given dates at regular intervals. 

epoch — a date chosen for reference purposes in quoting astrono- 
mical data which vary with time, e.g., the position of the 
equinox, or the elements of an orbit, are always quoted for a 
certain epoch. 

equator — the celestial equator is the great circle on the celestial 
sphere which is the projection of the terrestial equator. 

equatorial — a telescope arranged to rotate about an axis parallel 
to the Earth's axis, so that as it turns it will keep a star con- 
stantly in the field of view as it moves from east to west across 
the sky. 

equinox — one of the points of intersection of the equator and 
ecliptic; also the times at which the Sun passes through these 
points, the vernal equinox occurring on 20 or 21 March, the 
autumnal equinox on 23 September. The vernal equinox or 
First Point of Aries is the origin from which right ascension 
and longitude are measured. 

escape velocity — the least velocity which an object must acquire, 
at a given distance from a centre of attraction (e.g., Sun or 
planet), in order to escape from the gravitational field of the 
attracting body in a parabolic orbit. This parabolic velocity 
depends on the distance, and is 1-414 times the velocity in a 
circular orbit at that distance. 

evening star — (1) the planets Mercury or Venus when seen in the 
western sky at sunset; (2) also used more loosely to describe 
any planet which (after opposition) transits before midnight. 

expansion of the universe — the recession of the extra-galactic 
nebulae, at rates which are proportional to their distances, is 
taken as evidence that the universe is continuously expanding. 
See red shift, Hubble 's constant. 

extra-galactic nebulae — the nebulae that lie outside our Galaxy; 
they are themselves galaxies, and tend to form clusters. 

First Point of Aries — see equinox. 


flares {solar) — brief but very bright outbursts of hydrogen, seen on 
the Sun, usually in the neighbourhood of sunspots; often cause 
radio fade-outs and magnetic disturbances on Earth. 

flare stars — stars whose spectra show outbursts of light of a similar 
nature to solar flares, but on a much greater scale. 

free fall — the normal state of motion in an orbit in space under the 
gravitational attraction of a central body. In free fall, the 
vehicle is not driven, and everything within it is in a state of 
zero gravity. 

frequency — the number of waves passing a given point every 
second. The product of frequency and wave length gives the 
velocity of the waves. 

galaxies — the name now used for the extra-galactic nebulae; it is 
estimated that 10,000 million galaxies are observable. 

Galaxy — (1) the Milky Way; (2) the entire system of gas, dust and 
stars, of which the Sun is one; it is now known to have a spiral 

gauss — the unit in which the intensity of a magnetic field is 
measured. The Earth's magnetic field varies over the surface 
from about 0-3 to 0-6 gauss. 

gegenschein — a faint glow in the sky sometime seen on the ecliptic 
opposite the Sun. It appears to be connected with the zodiacal 
light, and is sometimes called the counterglow. 

Geiger counter — a gas-filled tube which permits an electric charge 
to pass through it when the gas is ionized; used for counting 
the number of charged particles that enter it. 

geocentric — having the centre of the Earth as origin or as view- 

giant stars — stars which are more luminous (and therefore have a 
greater surface and size) than the main sequence stars of the 
same spectral type. 

great circle — a circle on the celestial sphere which divides the 
sphere into two equal hemispheres, e.g., the horizon, the 


equator, the ecliptic. The shortest distance between two points 
on the celestial sphere is an arc of a great circle. 

Greenwich Mean Time (G.M.T.) — mean solar time, measured 
from the meridian of Greenwich and reckoned through 24 
hours from Greenwich midnight; it is identical with Universal 

Ha. (hydrogen alpha) — one of the lines of the hydrogen spectrum; 
it is prominent in the spectrum of the Sun (at 6563 a) and gives 
the red colour to the chromosphere and prominences. 

harvest moon — in the northern hemisphere the Full Moon which 
occurs nearest to the autumnal equinox, when the Moon rises 
on successive nights at about the same time. The same pheno- 
menon occurs in March-April in the southern hemisphere. 

heliocentric — having the Sun as origin; viewed from the centre of 
the Sun. 

horizon — the great circle on the celestial sphere which is every- 
where 90° from the zenith; the observed horizon will differ 
from this because of obstructions or the height of the observer. 

hour angle — the angular distance of a celestial body from the 
meridian, measured along the equator westwards in hours, 
minutes and seconds; it is found by subtracting the right 
ascension of the body from the local sidereal time. 

Hubble' s constant— the factor of proportionality in Hubble's Law 
connecting the velocity of recession of the galaxies with their 
distance. Recent work suggests a value of 55 km/sec per 
million light-years, and this leads to a figure of about 6,000 
million years since the recession began, i.e., when the galaxies 
were almost in contact. See expansion of the universe. 

Hunter's Moon — the Full Moon following the harvest moon, at 
which time conditions are often very similar. 

hydrogen I and 77— the hydrogen of interstellar space is either 
neutral atomic hydrogen (hydrogen I), or ionized hydrogen 
(hydrogen II). Hydrogen I is observable only by means of the 


21 centimetre radio line; hydrogen His found in the neighbour- 
hood of very hot stars, and is readily photographed. 

inferior planets — Mercury and Venus, which are inferior in the 
sense of revolving in orbits smaller than the Earth's. 

inner planets — the planets Mercury to Mars; a loose term used to 
distinguish them from the outer planets, which lie at much 
greater distances from the Sun. 

interferometer — an instrument for making very small measure- 
ments by utilizing interference fringes. Two rays of light 
travelling along different paths from the same source may 
reinforce or cancel each other, so producing alternate light 
and dark bands, the distance between which is a measure of 
the difference in the two paths of the light rays. The optical 
interferometer has been used for measuring the diameters of 
some supergiant stars ; similar principles are used in the inter- 
ferometers used in radio astronomy. 

interplanetary matter — a term which may be used to include 
comets, meteoric dust, cosmic rays, dust, electrons, etc., and 
which emphasizes the fact that space is not empty. 

interstellar hydrogen — the commonest element in the universe — 
see hydrogen I and II. 

ionization — the production of electrically charged particles from a 
neutral atom or molecule. In astronomy the ions of the metals, 
and of hydrogen and other gases are of the most frequent 
reference; these are ionized by the loss of electrons, producing 
positively charged ions. 

ionosphere — the upper region of the Earth's atmosphere, in 
which the gases are largely ionized. Several layers (F-layer, 
E-layer, D-layer) are recognized, and these have the property 
of reflecting radio-waves, so making long-distance short-wave 
communication possible. 

island universes — an old term for the extra-galactic nebulae. 

isophotes — lines which connect points of equal light intensity on a 


graph or chart; the effect is to produce a kind of contour map 
which indicates levels of brightness. 

kiloparsec — a thousand parsecs ; about 3,260 light-years. 

latitude — (1) on Earth, the angular distance north or south of the 
equator; (2) celestial latitude is the angular distance north (+) 
or south (— ) of the ecliptic. 

librations — apparent oscillations of the Moon on its axis, due to 
the inclination of the orbit of the Moon, and to its varying 
velocity. The term is also used of other forms of oscillation of 
planets or satellites. 

light-time — the time taken by light to travel from a celestial object 
to the observer. This may vary from a little more than a second 
in the case of the Moon, to many thousands of millions of 
years in the case of some of the distant galaxies. 

light-year — the distance that light travels in a year at a speed of 
186,000 miles a second. It amounts to 5,880,000,000,000 miles 
or 63,240 astronomical units. The nearest known star (Proxima 
Centauri) is at a distance of 4-3 light years. 

line of sight velocity — see radial velocity. 

local group — a cluster comprising nearly a score of galaxies, of 
which our Galaxy is one; the group also includes the Andro- 
meda nebula and the Magellanic clouds. 

longitude — (1) on Earth, the angular distance east or west of the 
meridian of Greenwich; (2) celestial longitude is the angular 
distance, measured along the ecliptic from 0° to 360°, east- 
wards from the equinox. 

luminosity — the actual output of light of a star, as opposed to the 
apparent brightness measured on Earth by an observer. 

Lyman alpha — the first (longest wavelength) of a series of lines in 
the ultra-violet spectrum of hydrogen. 

Lyot filter — a light filter used in viewing the Sun; it allows the 
passage of light of a very restricted wave-length band (usually 
that of Ha) and permits direct observation of the sun's chromo- 


M — Messier. An abbreviation applied to the number of a nebula 
in Messier's catalogue. 

Magellanic clouds — two large irregular nebulae visible to the naked 
eye in the southern hemisphere; these are the two nearest 

magnetic field — the entire space in which magnetic forces can be 
detected; apart from the Earth's magnetic fields, there are 
known to be strong magnetic fields associated with sunspots 
and certain stars, and there is believed to be a magnetic field 
in interstellar space. 

magnetic storms — large scale disturbances in the Earth's magnetic 
field, associated with solar activity; usually accompanied by 
displays of aurorae and the disruption of radio and tele- 
graphic communication. 

magnitude — the measure of apparent brightness of a star or planet. 
The naked eye can appreciate stars down to magnitude 6, 
but the 200-inch telescope can photograph stars a little fainter 
than magnitude 22. A difference of one magnitude represents 
a ratio of brightness of 2-512; an increase of 5 magnitudes 
therefore indicates a hundred-fold decrease in brightness. 
Absolute magnitude is the magnitude a star would have if it 
were seen from a standard distance of 10 parsecs. 

main sequence — if the stars are arranged in order of increasing 
absolute magnitude, the vast majority of them form a pro- 
gressive sequence of decreasing temperature, size and bright- 
ness; this main sequence is best displayed on a graph of 
absolute magnitudes against spectral type, colour index or 
temperature. The Sun belongs to the main sequence. 

mass spectrometer — an instrument for determining the masses of 
positively charged particles (e.g. metal ions) by measuring their 
displacement in a combined magnetic and electrostatic field. 

mean place — the position of a star as given in a star catalogue is a 
mean place, referred to some particular epoch and equinox. 
The effects of precession, nutation, aberration and (where 


appreciable) of parallax, proper motion and orbital motion 
have been removed ; these can be re-calculated for any future 
date, and when added to the mean place give the apparent 
place for that date. 

mean solar time — a uniform measure of time denned by the hour 
angle of the mean sun; see G.M.T. 

mean sun — an imaginary body which moves round the celestial 
equator at a uniform speed equal to the average rate of motion 
of the true Sun round the ecliptic. 

meridian — the great circle on the celestial sphere which passes 
through the poles and the zenith, intersecting the horizon at 
the north and south points. The term is generally used only of 
the upper meridian, i.e., that part of the meridian from the 
south point, up through the zenith to the pole. 

meteor — a 'shooting star' ; not a star, but a small particle which 
enters the Earth's atmosphere from outer space, and is 
destroyed by friction, leaving a luminous streak in the upper 
atmosphere; height 40 to 90 miles, speed 10 to 40 miles per 
second. The very bright meteors are called fireballs, or (if 
they explode) bolides. Most meteors are sporadic, but certain 
streams of meteoric dust are known, whose orbits about the 
Sun are intersected by the Earth each year. The resulting 
increase in the number of meteors, which will all come from 
some particular radiant, is known as a meteor shower. Meteors 
are also detected by radar methods and some daylight showers 
are of great interest. 

meteorite — a solid body of iron or stone which falls on the 
Earth's surface from outer space ; meteorites are thought to be 
of a different nature from the average meteor, and are probably 
derived from minor planets rather than comets. 

Metonic cycle — a period of nineteen years, after which the whole 
cycle of phases of the Moon repeats on the same days of the 
year; named after the Greek astronomer Meton (c. 432 B.C.). 

micrometeorites — fine dust of a meteoric origin, but too fine to be 
destroyed by friction in the atmosphere. 


micron — a unit of length equal to one thousandth of a millimetre. 

midnight sun — a popular term for the appearance of the Sun above 
the horizon all night in high latitudes; the phenomenon is 
visible at some period of the year from all places within the 
Arctic or Antarctic circles. The Moon and planets can, of 
course, display the same phenomenon. 

Milky Way — the band of light extending round the sky, which is 
shown by the telescope to consist of countless faint stars ; it 
represents our view of the Galaxy in which we are immersed. 

minor planets — a swarm of small bodies, less than 500 miles in 
diameter, most of which revolve about the Sun between the 
orbits of Mars and Jupiter. About 1,600 have well-defined 
orbits, but their total number probably runs into hundreds of 
thousands. Also called asteroids. 

month — the average period of revolution of the Moon about the 
Earth; it bears no relation to the calendar month. The length 
of the month depends on the point of reference; the more 
important are the sidereal month, referred to the stars, of 
27-32 days, and the synodical month, referred to the Sun, and 
giving 29-53 days between similar phases. Owing to the varia- 
tions in the Moon's orbit, the actual length of the month may 
vary considerably. 

morning star — Mercury or Venus, when seen in the eastern sky 
before dawn. Also used as a loose description of any planet 
which transits after midnight (i.e., before opposition). 

Nautical Almanac — the navigational ephemeris, giving astrono- 
mical information in a form suitable for use by navigators. 

nebulae — originally the term referred to any hazy patch of light 
among the stars; it is now restricted to the gaseous nebulae 
(either bright or dark) which are found in or near the Milky 
Way, and are irregular in outline. The extra-galactic nebulae, 
more regular in shape, show the spectrum of starlight, and are 
galaxies (spiral, elliptical, etc.); they are found in all parts of 
the sky. 


neutrons — the neutral particles which, together with protons, form 
the nuclei of atoms. 

node — the points at which the orbit of a planet, comet, satellite, 
etc., intersects the plane of the ecliptic (or other great circle of 

nova — a star which appears suddenly in the sky. Sometimes 
called 'new' or 'temporary' stars, but the appearance is due 
to an intense outburst of light from the surface of an unstable 
star. A score or more appear every year in our Galaxy. See 
also supernova. 

nucleus — the massive part of an atom, composed of protons and 
neutrons. The term is also applied to the denser parts of the 
head of a comet or other luminous object. 

nutation — a nodding of the Earth's axis ; a small irregular oscilla- 
tion of the pole about its mean position, and therefore addi- 
tional to the slow uniform motion of precession. 

obliquity of the ecliptic — the angle between the equator and the 
ecliptic; may be regarded as the angle at which the Earth's axis 
is tilted. 

occultation — the disappearance of a star (or other body) by the 
passage in front of it of a nearer body of larger apparent size. 
The most important occultations are those of stars, planets, 
and radio sources by the Moon. 

opposition — a superior planet is at opposition when its longitude 
differs from that of the Sun by 180°. 

outer planets — a term used for the planets Jupiter to Pluto. 

parabolic velocity — see escape velocity. 

parallax — the apparent change in the position of an object on the 
celestial sphere caused by a change in position of the observer. 
Annual parallax is the change in position of a star due to the 
annual motion of the Earth, and is the angle subtended by the 
radius of the Earth's orbit; generally called simply parallax. 
Horizontal parallax of the Moon or of a planet is the angle 
subtended at that body by the Earth's equatorial radius. 


parsec — the distance at which the (annual) parallax of a star is 
1 second of arc. It is a large unit, equal to 206,265 astrono- 
mical units, or 3-26 light-years. 

penumbra — the outer diffuse region of the shadow of the Moon 
or of a planet, where some light is still received from the Sun; 
the term is also applied to the outer regions of a sunspot. 

perigee — that point in the orbit of the Moon, or of an artificial 

satellite, which is nearest to the centre of the Earth. 
perihelion — that point in an orbit in the solar system which is 

nearest to the Sun. 
perturbations — disturbances in the regular orbital motion of a 

planet, comet, etc., caused by the gravitational attraction of 

other bodies. 

phases— the changing shape of the illuminated part of the Moon 
(or of a planet or satellite) due to the relative positions of Sun, 
Moon and Earth. The Moon and the inferior planets show all 
the phases from new (when the body is invisible) through 
crescent, quarter, gibbous to full, decreasing through gibbous, 
quarter to crescent and new again. The superior planets and 
their satellites show only the full and gibbous phases. 

photoelectric cell — an electronic device in which the incidence of 
light causes a change in an electric current. 

photoelectric photometry — an important branch of modern photo- 
metry in which the photoelectric cell is used to measure stellar 
magnitudes, etc. 

photographic zenith tube (P.Z.T.) — a fixed telescope directed to 

the zenith, used for photographing stars as they pass overhead 

for the exact determination of time. 
photometry — the measurement of the apparent brightness of a 

distant source, such as a star, by comparison with that of a 

source of known intensity. 
photomultiplier — a complex form of photoelectric cell, giving 

enormous amplification of the initial current. 
photon — the smallest amount (or 'quantum') of light energy. It 


may be thought of as a particle whose mass depends on the 
frequency, or as a short train of waves. 

plage — bright hydrogen or calcium clouds that are observed near 
sunspots in the Sun's chromosphere; originally called 'bright 

planet — a large, cold, solid body, moving in an elliptical orbit 
about the Sun, and shining solely by reflected sunlight. In 
addition to the nine major planets, many hundreds of minor 
planets are regularly observed. 

polarization — the process by which light or radio waves are 
restricted to vibrations in one direction (or plane) only. 

pole — the celestial poles are the points on the celestial sphere 
towards which the axis of the Earth is directed. The word is 
also used with reference to any great circle; the diameter of the 
sphere which is perpendicular to the great circle will intersect 
the sphere at two points called poles. 

Populations I and II— a term used by Baade to distinguish two 
main types of stars. Population I contains the hot blue-white 
stars found in the arms of spiral galaxies; Population II stars 
are the older red stars found in the central regions of galaxies 
and in globular clusters, where dust and gas are absent. 

position angle — the direction of one object from another; mea- 
sured from the north point of the principal object through east 
from 0° to 360°. 

precession — the slow twisting of the Earth's axis in space, the pole 
describing a circle round the pole of the ecliptic in a period of 
about 26,000 years. This does not alter the relative positions 
of the stars, but causes the equinox to move westwards round 
the ecliptic, so that the positions of the stars with respect to 
the equator (i.e., the R.A. and dec.) or the horizon change 
slowly with time. 

primary focus — (prime focus) — the focal plane of the objective or 
main mirror of a telescope; the term indicates that the instru- 
ment is used without an eyepiece or any other lens or mirror. 


profile, line — a tracing of the intensity of the image of an emission 
line; measured across the line it reveals the fine structure in 

proper motion — the motion of a star at right angles to the line of 

sight; the actual change of position of the star due to its real 

motion in space. 
proton — the positively charged particle which forms the nucleus 

of the hydrogen atom. The nuclei of other atoms are composed 

of protons and neutrons. 

pulsating stars — variable stars, both irregular and of the cepheid 
type. Such stars are believed to expand and contract, and are 
brightest when contracted. The behaviour is not, however, 
completely understood. 

quadrature — the positions of two celestial bodies when their direc- 
tions from the observer are at right angles ; generally used of the 
Moon or a planet when at an elongation from the Sun of 
90° or 270°. 

radial velocity — the velocity of a star towards, or away from, the 
observer; measured by the Doppler effect in the star's spec- 

radiant — the point (or small area) from which the tracks of the 
meteors in a meteor shower appear to originate. This is an 
effect of perspective (as in the case of railway lines), the paths 
of all the meteors in the shower being sensibly parallel. 

radio astronomy — the study of radio waves received from the Sun, 
planets, interstellar hydrogen, and more distant galactic 
sources; also the use of radar methods in studying the Moon, 
planets, meteors, etc. 

radius vector — the line joining any body revolving in an orbit to 
its centre of attraction, as the line joining a planet to the Sun. 

red shift — the extra-galactic nebulae show a displacement of their 
spectral lines towards the red end of the spectrum. This is 
interpreted as a Doppler effect, indicating that all these galaxies 
are receding from us. See expansion of the universe. 


reflector — a reflecting telescope, in which the initial image is 

formed by reflection from the upper surface of a spherical or 

parabolic mirror. 
refractor — a refracting telescope, in which the image is formed by 

refraction through the main lens, called the object glass or 

refraction — the bending of a ray of light when it passes from one 

transparent medium to another. 

resolving power — the ability of an optical instrument to show fine 
detail or to separate the images of very close objects; resolving 
power depends on the aperture of the instrument. 

retrograde motion — (1) the apparent westerly motion of a planet 
among the stars caused by the easterly motion of the Earth; 
with a superior planet, opposition occurs about the mid-point 
of the retrogression. With the inferior planets, retrograde 
motion occurs at the time of inferior conjunction, and is not so 
readily observed. (2) True retrograde motion occurs in the 
orbits of comets and satellites which have inclinations greater 
than 90°. 

revolution — orbital motion about a centre of attraction, as in the 
revolution of the Earth about the Sun. 

right ascension — the angular distance of a body from the equinox, 
measured eastwards along the celestial equator, and usually 
expressed in hours, minutes and seconds up to 24 hours. 

rotation — the turning of a body about its axis; thus the Earth 
rotates about its axis, but revolves about the Sun. 

Saros — the eclipse cycle of 6,585-3 days (18 years and lOorll days) 
after which Sun and Moon return to the same relative positions 
with respect to the Moon's node, and the entire series of 
eclipses repeat in the same order and under similar conditions. 
During one Saros there are about 70 eclipses, 41 of the Sun 
and 29 of the Moon. 

Schmidt telescope — a reflector in which the surface of the main 
mirror is part of a sphere, and the resulting aberrations are 


corrected by a thin glass correcting plate placed before the 

semidiurnal arc — the angle (or the time) required by a celestial 
object to describe its apparent motion across the sky from 
rising to transit, or from transit to setting. 

sidereal day — the interval between two successive transits of the 
same star; it is equal to 23 h 56 m 04 s 09 of mean solar time, and 
the difference from 24 hours causes the stars to rise and set 
4 minutes earlier each day. 

sidereal period — the period of a planet or comet measured with 
respect to the stars. 

sidereal time — time measured by rotation of the Earth with respect 
to the stars. The sidereal time at any place is equal to the right 
ascension of an object on the meridian at that time. 

solar motion — the motion of the Sun (with reference to the neigh- 
bouring stars) of about 12 miles per second towards the con- 
stellation Hercules ; the term is also used of the Sun's share in 
the rotation of the Galaxy, which carries it towards the stars 
of Cygnus at about 130 miles per second. 

Solar System — the Sun, with its family of planets, comets, meteors, 
satellites, dust and gas, all of which are controlled by the Sun's 
gravitational attraction and are influenced by its radiation. 

solar parallax — the horizontal parallax of the Sun; it amounts to 
8"-79, from which is derived the distance of the Earth from 
the Sun. 

solstice — the place (or the time) at which the Sun reaches its 
greatest declination north (summer solstice) or south (winter 

spectral types — the main types of stellar spectra, arranged in order 
of decreasing temperatures, are denoted by the letters O-B-A- 
F-G-K-M-R-N-S, each group being further subdivided by the 
use of small letters or of figures from to 9. There is thus a 
progression from the hot blue-white helium stars, through the 


hydrogen stars of type A to the stars of type G, like the Sun, 
in which numerous metallic lines are seen; the stars of later 
types become cooler and redder, and show absorption bands 
due to molecules such as titanium oxide and carbon com- 

spectrograph — an instrument for photographing spectra. 

spectroheliograph — an instrument for photographing the Sun in 
the light of one particular wave-length, giving, for example, 
the appearance of the hydrogen or calcium clouds of the 

spectrohelioscope — an instrument for continuously viewing the Sun 
in the light of one wave-length. 

spectroscopic binaries — binary stars which are so close together as 
to be invisible in the telescope, but which are so placed that 
their double spectra can be studied by means of the Doppler 

spectrum — the rainbow band of colours produced when white 
light from a small source is passed through a glass prism is 
really a series of overlapping images of the source, each differ- 
ent colour corresponding to a definite wave-length. Only an 
incandescent substance produces this continuous spectrum; a 
single element in the gaseous state produces a line spectrum, 
i.e., only certain wave-lengths are present, as coloured lines. 
The positions of these lines serve to identify the element. See 
also emission lines, absorption lines, Doppler effect. 

star — a self-luminous globe of gas of the same general nature as 
the Sun, although it may differ in size and temperature, etc. 
There are probably a hundred thousand million stars in our 

stationary point — a point in the apparent path of a planet at which 
it appears to be stationary in longitude (but may still be 
moving in latitude). Stationary points occur at the beginning 
and end of the period of retrograde motion, i.e., before and 
after opposition or inferior conjunction. 


steady-state theory — see continuous creation. 

Sun — a star of spectral type G and absolute magnitude +5. It is 
a sphere of intensely hot gas, about 864,000 miles in diameter; 
the surface temperature is about 6,000°C but must rise to many 
millions of degrees in the interior. The visible surface is the 
photosphere, above which lie the chromosphere and the corona. 
The Sun rotates, in the same direction as the planets revolve, 
in about 25 days. 

sunspot — a dark spot appearing on the Sun; the dark centre (the 
umbra) is surrounded by the lighter penumbra, but they only 
appear dark by contrast with the brilliant solar surface. A 
sunspot may be as much as 100,000 miles or more across. 

sunspot cycle — the number of sunspots shows a marked tendency 
to maximum about every eleven years ; there are considerable 
variations both in the numbers and the period. 

supergiant stars — intensely luminous stars of low density and great 
size; their constitution and evolution appear to be different 
from that of ordinary stars. 

superior planets — the planets from Mars to Pluto, which revolve in 
orbits larger than that of the Earth. 

supernova — an exceptionally brilliant nova, rare in our Galaxy, 
but so brilliant that about 50 have been observed in other 
galaxies. The Crab nebula is the remains of a supernova 

synchrotron — a machine for accelerating charged particles in a 
combined electrostatic and magnetic field. At very high 
energies, an electron beam produced in this way gives out a 
blue glow which is called synchrotron radiation. 

synodic period — the time taken by a planet or satellite to return to 
the same relative positions with respect to the Sun and Earth; 
hence the average interval between oppositions or conjunctions. 

terminator — the line separating the dark and illuminated sides 
of a planet or satellite. The terminator on the Moon is quite 


sharp, indicating the absence of any appreciable atmosphere; 
the Sun is rising on the terminator before Full Moon, and is 
setting on this line afterwards. 

transit — the passage of any celestial body across the meridian ; also 
used for the passage of a satellite or its shadow across the face 
of a planet, or of Mercury or Venus across the face of the Sun. 

twilight — the illumination of earth and sky which lasts from sunset 
until darkness, and from darkness until sunrise; there would be 
no twilight in the absence of an atmosphere, as on the Moon. 
Theoretically, darkness begins and ends when the Sun is 18° 
below the horizon, but in this country in the summer months 
the Sun is not depressed to this extent, and there is a certain 
amount of twilight throughout the night. 

umbra — the central dark part of the shadow of the Moon or of a 
planet, where no light is received from the Sun; also applied to 
the darker central region of a sunspot. 

U.T. — universal time — see G.M.T. 

variable stars — stars whose light varies because of some internal 
cause; the eclipsing binaries are also variable, but are generally 
treated as a separate class. See cepheids, cluster-type variables, 

wavelength — the distance between successive troughs or crests in a 
wave motion; the velocity of the wave is given by frequency 
multiplied by wavelength. See angstrom unit. 

W-type stars — see Wolf-Rayet stars. 

white dwarfs — very small faint stars of extraordinarily high den- 
sity; the normal structure of the atoms in these stars has 
broken down, and they contain nuclei and electrons packed 
together as tightly as possible. Their masses are about the 
same as that of the Sun, but the density may rise to millions 
of times that of water. Such stars appear to be very common, 
but are faint and difficult to detect. The best known example is 
the companion oiSirius. 


Wolf-Ray et stars — a small group of stars of very high temperature, 
whose spectra (type W) show broad bright emission lines. It is 
believed that the stars are surrounded by expanding shells of 
year — the period of the Earth's revolution about the Sun. 
Measured from equinox to equinox it amounts to 365-2422 
days, and the civil calendar, with its rules for leap-years, is 
designed to allow for the extra decimal of a day. 

Zeeman effect — the splitting of a spectrum line into a number of 
components when the source of light is subject to a strong 
magnetic field ; it is observed in the spectra of sunspots. 

zenith — the point on the celestial sphere which is directly overhead, 
as determined by a plumb-line. 

zodiac — a belt of the sky about 8° wide on either side of the ecliptic, 
in which the Sun, Moon and major planets are always to be 

zodiacal light — a faint luminous band of light along the ecliptic 
stretching outwards from the Sun; best seen after sunset or 
before sunrise. Its spectrum is that of reflected sunlight, and 
it appears to consist of small particles, forming an extension 
of the solar corona. 

Some Interesting Telescopic Objects 

The owner of a small telescope must not expect too much from his 
instrument. Those wonderful photographs of nebulas which are 
used to illustrate text-books are taken with long exposures with 
large telescopes, and the photographic process can reveal far more 
than the eye can ever see. However, there is plenty to look for in 
the sky, and any instrument, however small, will show a great deal 
of the wonder and beauty of the universe around us. 

A telescope is seldom satisfactory for the study of large clusters 
and groups of stars because the field of view is too small. A pair 
of binoculars is easier to handle, and will give magnificent views of 
open clusters such as the Pleiades, the colours of some of the more 
brilliant stars such as Betelgeuse and Antares, and the fascinating 
chains and lines of stars in many parts of the Milky Way, especi- 
ally in Aquila, Cassiopeia, Cygnus, Lyra and Perseus. 

In the following list, which makes no pretence of being com- 
plete, some of the more interesting telescopic objects are arranged 
in order of right ascension. They may all be found on a suitable 
star atlas, such as Norton's Star Atlas (Gall & Inglis), and posi- 
tions have been given for the benefit of those observers who have 
telescopes equipped with setting circles. 

Alpha Cassiopeia (Shedir). R.A. h 38 m -5, Dec. +56° 20' 

A K-type star in the W. of Cassiopeia. It is an irregular variable, 
fluctuating between magnitude 2-1 and 2-7, though its normal 
magnitude is about 2-3. Generally speaking, the variations are 
very slow, and there is some doubt whether they are real. Beta 
Cassiopeia; (magnitude 2-42) is a useful comparison star. The 
orange hue of Shedir is well brought out with binoculars. 


Messier 31 Andromeda. R.A. h 40 m -7, Dec. +41° 05' 

The Great Spiral, faintly visible to the naked eye not far from 
the 4th-magnitude star Nu Andromedae. It is one of the closest of 
the external galaxies, and lies at a distance of about 2 million 
light-years. It must be admitted that in any small or moderate 
telescope it is a disappointing object, and photographs taken with 
large instruments are needed to show the spiral form adequately. 

H.VIII. 78 Cassiopeia. R.A. h 41 m -3, Dec. +61° 36' 

A fine star-cluster, between Gamma and Kappa Cassiopeia?. 
A small telescope will show it well. 

Gamma Cassiopeia. R.A. h 54 m -5, Dec. +60° 31' 
A most extraordinary star, with a spectrum which is classed as 
BO (peculiar). It is regarded as a pseudo-nova, since it sometimes 
undergoes outbursts - for instance in 1936, when it rose to magni- 
tude 1-6. Its normal magnitude is between 2-3 and 2-8. Useful 
comparison stars are Beta Cassiopeia? (2-42) and Delta (2-80). 

Messier 33 Trianguli. R.A. l h 31 m -8, Dec. +30° 28' 

One of the closest of the external galaxies, and a member of the 
Local Group. Photographs reveal that it is a spiral. In moderate 
telescopes it is a faint and very difficult object. 

Gamma Arietis. R.A. l h 51 m -5, Dec. +19° 07' 

An excellent double. Magnitudes 4-2, 4-4; position angle 000°; 
distance 8"-4. Any small telescope will show both components 
well. It is easy to locate, as it lies close to Beta Arietis. 

Alpha Ursa Minoris (Polaris). R.A. l h 58 m -6, Dec. +89° 06' 

The Pole Star. It is of magnitude 2 0, but is actually a cepheid 
variable of sm all range. The spectrum is F8 . It has a ninth-magnitude 
companion (p.a. 217°, distance 18"-3) visible with a 3-inch tele- 
scope ; it is said to be visible even with a 2-inch. 

Gamma Andromeda. R.A. 2 h 01 m -7, Dec. +42° 09' 
A superb double. The primary is a K-type star of magnitude 


2-3; the companion is of magnitude 5, and is bluish (p.a. 061°; 
distance 9"-7.) The companion is itself a close binary; distance 
0"-5, period 55 years. The main pair forms a superb object in a 
moderate telescope. 

H.VI 33-4 Persei. R.A. (for H.VI. 33) 2 h 18 m -3, Dec. +56° 59' 

Twin clusters in the 'Sword-Handle' of Perseus; just visible to 
the naked eye. Each is about 45' in diameter. Small telescopes will 
show them adequately; they form one of the most magnificent 
spectacles in the whole sky. Between the two clusters lies a reddish 

Omicron Ceti (Mira). R.A. 2 h 17 m -5, Dec. -3° 08' 

The famous variable star. It has an average period of 331 days, 
and its magnitude range is from 1-6 to 9-6. However, neither the 
period nor the magnitude range may be regarded as at all constant; 
at some maxima the magnitude never exceeds 5. The spectrum is 
of type Me, and the reddish colour makes Mira easy to identify. 

Iota Cassiopei/e. R.A. 2 h 26 m -l, Dec. +67° 15' 
A triple star. Magnitudes 4-2, 7-0, 80, p.a's. 251°, 113°; dis- 
tances 2"-4, 7".4. Excellently seen with a moderate telescope. 

Rho Persei. R.A. 3 h 02 m -9, Dec. +38° 42' 

An M-type irregular variable, not far from Algol. The magni- 
tude range is from 3-4 to 4-1; Kappa Persei (40) makes a good 
comparison star. The reddish hue is well brought out in binoculars. 

Beta Persei (Algol). R.A. 3 h 05 m -8, Dec. +40° 49' 
The 'Demon Star', the prototype eclipsing binary. Its period is 
2-87 days. For most of this time it is of magnitude 2-3; it then 
drops to 3-5 in five hours, and after minimum takes another five 
hours to climb back to maximum. Algol may be studied with the 
naked eye, and its apparent fluctuations are interesting to follow. 

Eta Tauri (Alcyone). R.A. 3 h 45 m -3, Dec. +24° 00' 
The brightest star in the Pleiades (Seven Sisters), the most 


conspicuous open cluster in the sky. Keen-sighted persons will be 
able to see at least eight Pleiads with the naked eye. The best views 
of the cluster are obtained with binoculars or very low powers on 
a telescope. The names of the other leading stars in the Pleiades are 
Electra, Atlas, Merope, Maia, Taygete, Celceno, Pleione and 

Alpha Tauri {Aldebaran). R.A. 4 h 33 m -9, Dec. +16° 26' 

A K-type reddish star of magnitude 0-85. It is 57 light-years 
distant, and is ninety times as luminous as the Sun. Extending 
from it in a rough V are the stars of the very loose cluster known 
as the Hyades ; one of these (Theta Tauri) is a naked-eye double. 
Aldebaran has a faint companion (magnitude 1 1 ; p.a. 034°, dis- 
tance 121"). Actually, Aldebaran is not a true member of the 
Hyades group, and lies between the cluster and ourselves. 

Epsilon Auriga. R.A. 4 h 59 m -4, Dec. +43° 46' 

The leading member of the 'Haedi' or Kids, a triangle of three 
faint stars close to Capella. Epsilon is an eclipsing binary; the 
magnitude range is from 3-3 to 4-1, and the period is over 27 years. 
One component is a very luminous F-type supergiant. The fainter 
star is invisible, and appears to be the largest individual star 
known, with a diameter of over 1,800 million miles. 

Zeta Auriga. R.A. 5 h 00 m 0, Dec. +41° 01' 
The faintest member of the 'Hajdi'. It too is an eclipsing binary, 
though it is not so vast a system as Epsilon. The spectral types of 
the components are K0 and Bl. The mean magnitude is 40; the 
fluctuations are not easy to detect without instrumental aid. 

Kappa Leporis. R.A. 5" ll m -6, Dec. -12° 59' 
A double star; magnitudes 50, 7-5; p.a. 000°; distance 2"-6. 
The primary is yellowish ; the companion bluish. 

Beta Orionis (Rigel). R.A. 5 h 12 m -8, Dec. —8° 15' 

The leading star of Orion; magnitude 015. The distance is 
thought to be about 540 light-years. Rigel is exceptionally lumin- 



ous, and is the equal of at least 18,000 Suns. It has a B-type 
spectrum, and is almost pure white. There is a seventh-magnitude 
companion (p.a. 202°, distance 9"-4) easily seen in a 3-inch 

Alpha Auriga {Capella). R.A. 5 h 14 m 0, Dec. +45° 58' 

Magnitude 009; spectrum GO. Capella is of a yellowish hue, 
and is a superb object in binoculars. It is an extremely close binary. 
The distance is 47 light-years, and the luminosity 150 times that 
of the Sun. Apart from Arcturus and Vega, it is the brightest star 
in the northern hemisphere of the sky. 

Delta Orionis (Mintaka). R.A. 5 h 30 m -2, Dec. -0° 19' 
The upper star of Orion's belt; it lies almost on the celestial 
equator. The primary is an eclipsing binary of small range; 
average magnitude 2-4. There is a seventh-magnitude companion 
(p.a. 000°, distance 52"-8) which is a very easy telescopic object. 

Messier 1 Tauri. R.A. 5 h 32 m -3, Dec. + 22° 00' 
The 'Crab' Nebula; a fascinating object not far from the third- 
magnitude star Zeta Tauri. It is the wreck of a supernova which 
was observed by Chinese astronomers in the year 1054. In a small 
telescope it appears as a faint, diffuse object; large instruments 
reveal complex detail. The gas-cloud is still expanding from the 
old explosion-centre. 

Messier 42 Orionis. R.A. 5 h 33 m -4, Dec. -5° 24' 
In the Sword of Orion; the most prominent gaseous nebula in 
the sky. It is visible with the naked eye. Excellent views of it are 
obtained with low powers on small or moderate telescopes. It 
contains the famous multiple star Theta Orionis, the 'Trapezium' 
(R.A. 5 h 33 m , Dec. —5° 27') whose four components are visible in 
a 3-inch refractor. This superb nebula is always worth looking at. 

Iota Orionis. R.A. 5 h 33 m -7, Dec. -5° 56' 
A double star. Magnitudes 3-2, 7-3; p.a. 141°; distance 1T-4. 
This is the lowest star of Orion's Sword. 


Sigma Orionis. R.A. 5 h 36 m -9, Dec. -2° 37' 
Another fine multiple in Orion's Sword. Four stars (magnitudes 
4, 10, 7-5, 7) are fairly easy to see with a moderate telescope; larger 
instruments reveal several more. 

Zeta Orionis. R.A. 5 h 38 m -9, Dec. -1° 58' 
The lowest star of Orion's Belt. The 20-magnitude, B-type 
primary has a 50-magnitude companion; p.a. 157°, distance 
2"-8. This is a well-known test for a 2-inch refractor. 

Alpha Orionis (Betelgeuse). R.A. 5 b 53 m -2, Dec. +7° 24' 
A particularly interesting star. It is thought to be about 10,000 
times as luminous as the Sun, and 650 light-years away. The 
diameter is about 250 million miles, but this changes somewhat, 
as the star is an irregular variable. There is a rough period of about 
five years. The magnitude range is from 01 to 1-3. On very rare 
occasions Betelgeuse has been known to outshine Rigel. Its 
orange-red hue makes it a superb sight in binoculars or a low 

Messier 35 Geminorum. R.A. 6 h 06 m -5, Dec. +24° 21' 

A splendid open cluster near Mu and Eta Geminorum. This is 
one of the most spectacular cluster-type objects visible with small 

Eta Geminorum. R.A. 6 h 12 m -7, Dec. +22° 31' 

A long-period variable; period 231 days, range 3-3 to 4-2. The 
spectrum is of type M, and the colour orange-red. The neighbour- 
ing star Mu, magnitude 3-2 and also of type M, makes a good 
comparison. The variations of Eta are slow, but may be followed 
with the naked eye. 

Beta Monocerotis. R.A. 6 h 27 m -l, Dec. -7° 00' 
A triple star. Magnitudes 50, 5-5, 60; p.a. 132°, 105°, distances 
7"-4, 2"-8. A fine sight in a moderate telescope. 


H.VII. 2 Monocerotis. R.A. 6 h 30 m -7, Dec. +4° 53' 
A beautiful open cluster just visible to the naked eye. 

Alpha Canis Majoris (Sirius). R.A. 6 h 43 m -6, Dec. -16° 40' 

The brightest star in the sky. It is of magnitude — 1 -43, and has 
an AO-type spectrum; it is 26 times as luminous as the Sun, and is 
one of the closest of all stars, since its distance is only 8-6 light- 
years. It is a wonderful sight in binoculars. The famous com- 
panion, Sirius B, is a white dwarf, but unfortunately invisible 
except in large telescopes. 

Messier 41 Canis Majoris. R.A. 6 h 45 m -5, Dec. -20° 42' 
An open cluster, just visible to the naked eye and excellently 
seen with low powers. 

Zeta Geminorum. R.A. 7 h 02 m 0, Dec. +20° 38' 
A Cepheid variable. Its magnitude range is from 3-7 to 4-3, and 
its period is 10-2 days. Nu Geminorum (magnitude 4-1) is a useful 
comparison star. Zeta has a G-type spectrum, and is rather 

Alpha Geminorum (Castor). R.A. 7 h 32 m -3, Dec. +31° 58' 
The senior though fainter of the famous 'Twins'. It was ranked 
of the first magnitude by the old astronomers, but is now appreci- 
ably below; its magnitude is 1-6. It is a fine binary, with a period 
of 350 years; p.a. 204", distance 4". The individual magnitudes of 
the two components are 20 and 2-8. Each is a spectroscopic 
binary, and the faint eclipsing binary YY Geminorum (= Castor 
C) is also a member of the system. 

Beta Geminorum (Pollux). R.A. 7 h 43 m l, Dec. +28° 07' 
The orange hue of Pollux (spectrum K0) contrasts with the pure 
white of Castor. The magnitude is 1-2, the distance 32 light-years, 
and the luminosity 28 times that of the Sun. 

Messier 44 Cancri. R.A. 8 h 38 m , Dec. +20° 07' 
Praesepe, or the 'Beehive', is a fine open cluster. It is easily 


visible to the naked eye on a moonless night, close to the two faint 
stars Delta and Gamma Cancri. It is well seen with low powers, 
and is not difficult to resolve into separate stars. 

Alpha Hydr.e (Alphard). R.A. 9 h 25 m -8, Dec. -8° 30' 
Alphard, the 'Solitary One', is easy to locate; it lies more or less 
in line with Castor and Pollux, and is very isolated. Moreover it is 
of type K, and decidedly red. Alphard is a spectacular object when 
viewed with binoculars. 

Gamma Leonis. R.A. 10 h 18 m 0, Dec. +20° 01' 
A binary with a period of 407 years. The magnitudes are 2-4 
and 3-8; the p.a. 119°, and the distance 4". The star is easy to 
identify, as it lies in the famous Sickle of Leo, not far from 
Regulus. It is a fine sight in a moderate telescope. 

U Hydra R.A. 10 h 35 m -8, Dec. -13° 12' 
An N-type irregular variable, with a range from magnitude 
4-5 to 6. It is the brightest of the stars of spectrum N, and its deep- 
red colour makes it of great interest. 

Messier 97 Urs^e Majoris. R.A. ll h 12 m -6, Dec. +55° 13' 
The 'Owl' nebula. It is 3' in diameter, and is one of the interest- 
ing objects known as planetary nebulae. It is not, however, very 
conspicuous, and will hardly be seen in a small telescope. 

Gamma Virginis. R.A. 12 h 39 m -8, Dec. -1° 15' 
One of the most spectacular binaries in the sky. Each compo- 
nent is of type F0, and the magnitudes are almost equal at 3-6. The 
period is 180 years, and the separation is becoming steadily less, 
but it is still well over 5", so that the components are excellently 
seen in a small telescope. 

Alpha Canum Venaticorum (Cor Caroli). R.A. 12 b 54 m -3, 

Dec. +38° 31' 
An easy double. Magnitudes 3-1, 5-6; p.a. 228°; distance 19"-7. 


Zeta Urs^ Majoris (Mizar). R.A. 13 h 22 m -5, Dec. +55° 07' 

The second star in the Plough-handle. It forms a naked-eye 
pair with Alcor (magnitude 5). Mizar is itself a binary ; magnitudes 
2-2, 4-2; p.a. 150°, distance 14"-5. In any small telescope the 
components are easily separated. With low powers Alcor also is 
in the field, and between it and Mizar is yet another star. This 
is one of the best binary objects for small apertures, particularly 
as Mizar is so easy to locate. 

Messier 3 Canum Venaticorum. R.A. 13 h 40 m -6, Dec. 

+28° 34' 

A bright globular cluster on the borders of Canes Venatici and 
Bootes. With a moderate telescope, the cluster is fully resolvable 
into stars. 

Alpha Boons (Arcturus). R.A. 14 h 14 m 0, Dec. +19° 22' 
Apart from Sirius, Arcturus is the brightest star visible from 
the latitude of Britain. Its magnitude is —006, its distance 41 
light-years, and its luminosity 100 times that of the Sun. The 
spectrum is of type K, and Arcturus" glorious orange hue makes 
it a fine sight with binoculars or a low power. 

Epsilon Bootis. R.A. 14 h 43 m -4, Dec. +27° 14' 
A third-magnitude star with a sixth-magnitude companion at 
distance 2"-8, p.a. 335°. The primary is yellowish, the companion 

R CoronjE Borealis. R.A. 15 h 47 m -l, Dec. +28° 15' 
A curious irregular variable. For long periods the magnitude 
remains at 6, and then drops suddenly, sometimes to below 12. 
After a period of minimum brilliancy, which may be protracted, 
the star rises once more to magnitude 6. The causes of this beha- 
viour are unknown, and amateur observers can do valuable work 
by studying R Coronae and other stars of its type. 

T Corona Borealis. R.A. 15 h 58 m 0, Dec. +26° 01' 
The 'Blaze Star'. Normally it is of below magnitude 8, but it has 


suffered two major outbursts - one in 1866 (magnitude 2) and the 
other in 1946 (magnitude 4). Minor fluctuations are always going 
on, and the star merits close attention from amateur observers. 

Beta Scorpionis. R.A. 16 h 03 m -3, Dec. -19° 42' 
Magnitudes 30, 5-2; p.a. 023°; distance 14". This is a wide, 
easy double. 

Messier 80 Scorpionis. R.A. 16 h 14 m -9, Dec. -22° 53' 
A bright globular cluster between Antares and Beta Scorpionis. 
Well seen in a moderate telescope. 

Messier 4 Scorpionis. R.A. 16 h 21 m -5, Dec. -26° 26' 
An open cluster, close to Antares. The diameter is about 14', 
and the whole cluster is easily resolvable. 

Eta Draconis. R.A. 16 h 23 m -5, Dec. +61° 36' 
A G5-type star of magnitude 2-9, with an eighth-magnitude 
companion at p.a. 142°, distance 6"1. It is a test for a 3-inch 

Alpha Scorpionis (Antares). R.A. 16 h 27 m -2, Dec. -26° 21' 
The 'Rival of Mars'. Antares is an M-type supergiant, 3,400 
times as luminous as the Sun, and 360 light-years away. It is 
strongly red in hue, and has a seventh-magnitude greenish com- 
panion at p.a. 275°, distance 3". For some time Antares was 
believed to be the largest star known; though it is in fact surpassed 
by others, it is still of exceptional size. It is unfortunate that it 
never rises very high over the British horizon. 

Zeta Herculis. R.A. 16 h 39 m -9, Dec. +31° 40' 
A splendid binary with a period of 34 years. The distance 
reached l"-6 in 1954, and is now decreasing. The primary is a star 
of spectral type GO, magnitude 3; the companion is of magnitude 

Messier 13 Herculis. R.A. 16 h 40 m , Dec. +36° 31' 
The brightest of the globular clusters visible from the latitude 


of Britain. It may be seen with the naked eye on a clear night, and 
lies between Zeta and Eta Herculis, considerably closer to Eta. 
With a moderate telescope, it is fully resolvable, and is a magni- 
ficent sight, but in very small instruments it is somewhat dis- 

Alpha Herculis. R.A. 17 h 13 m 0, Dec. +14° 26' 

One of the most interesting stars in the sky. The primary is an 
M-type supergiant, variable between magnitudes 3 and 3-7 in an 
irregular manner ; it has the distinction of being one of the largest 
stars known. The companion (magnitude 6, p.a. 112°, distance 
4"-5) is distinctly green. In a moderate telescope the colours make 
a superb contrast. The fluctuations of the primary may be followed 
with the naked eye; Kappa Ophiuchi (magnitude 3-4) makes a 
useful comparison star. 

Messier 92 Herculis. R.A. 17 h 16 m l, Dec. +43° 11' 

A globular cluster between Eta and Iota Herculis. It resembles 
Ml 3, but is much less conspicuous. 

Messier 7 Scorpionis. R.A. 17 h 51 m -6, Dec. -34° 48' 

A magnificent open cluster near the Scorpion's 'sting'. Un- 
fortunately it is never well seen in Britain, as it is always low in 
the sky. 

Messier 23 Sagittarii. R.A. 17 h 54 m -8, Dec. -19° 01' 

An open cluster almost 50' in diameter, well seen with a low 

H.IV. 37 Draconis. R.A. 17 h 58»-6, Dec. +66° 38' 

One of the brightest of the planetary nebulae. If is well seen with 
a moderate telescope. 

Messier 8 Sagittarii. R.A. 18 h 01 m -4, Dec. -24° 23' 

The 'Lagoon' nebula. This is a gaseous nebula, and is contained 
in our own Galaxy. It is faintly visible with the naked eye, and 
moderate telescopes show a large amount of detail; there are 


bright patches and dark rifts. This whole area is rich in nebular 
objects, and is well worth sweeping. 

N.G.C. 6572 Ophiuchi. R.A. 18 h 10 m -9, Dec +6° 50' 
A small, bright planetary nebula, lying between Beta Ophiuchi 
and Zeta Aquilae. It is an easy object in a small telescope. 

Messier 17 Sagittarii. R.A. 18 h 18 m -8, Dec. -16° 12' 
The 'Omega' nebula. The nearest naked-eye star is Gamma 
Scuti. Like the Lagoon, this is a gaseous nebula contained in our 
own Galaxy, and is large and bright, with abundant detail. 

Alph,e Lyr^ (Vega). R.A. 18 h 35 m -7, Dec. +38° 45' 
Vega is the brightest star in the northern hemisphere of the sky, 
apart from Arcturus. Its magnitude is 0-0, its spectral type A0, its 
distance 26 light-years and its luminosity 50 times that of the Sun. 
It is notable because of the distinctly bluish cast which makes it a 
superb object in low powers. It has a companion of magnitude 
10-5, at p.a. 170°, distance 56". This is an optical pair, and not 
a binary; the companion is faint and moreover overpowered by 
the brilliance of the primary, so that it is not a particularly easy 
object. Vega is very high up during summer evenings, and cannot 
be mistaken. 

Epsilon Lyr^. R.A. 18 h 43 m -2, Dec. +39° 34' 
A fascinating quadruple star. Epsilon 1 and Epsilon 2 form a 
naked-eye pair (distance 208"), and are easy to find, since they lie 
near Vega. Each is again double; Epsilon 1 (magnitudes 4-6, 6-3; 
p.a. 005°; distance 3") and Epsilon 2 (4-9, 5-2; 111°; 2"-3) and there 
are various other stars in the same low-power field. This is a 
particularly good object for viewing with a small or moderate 

Zeta Lyr*. R.A. 18 h 43 m -5, Dec. +37° 34' 
A wide, easy double. Magnitudes 4-2, 5-5; p.a. 150°; distance 44*. 

Beta Lyr*. R.A. 18 h 48 m -8, Dec. +33° 19' 
The prototype 'ellipsoidal' variable. It is not in fact a true 


variable, but is an eclipsing binary of special type. The maximum 
is magnitude 3-4; the minima are alternately of magnitude 3-8 
and 41 ; the period is 12-9 days. Gamma Lyras (magnitude 3-3) is 
a useful comparison star. The system of Beta Lyrae is of particular 
interest from an astrophysical point of view. The spectra are B8 
and B2, but each is peculiar, and the components are too close to 
be separated visually. 

Messier 11 Scuti. R.A. 18 h 49 m 0, Dec. -6° 19' 

The 'Wild Duck'. A superb open cluster, not far from Lambda 
Aquilae. It is faintly visible to the naked eye. A moderate telescope 
shows it as a fan-shaped cluster, with a bright star at its apex. 

Messier 57 Lyr,e. R.A. 18 h 52 m -6, Dec. +32° 59' 

The 'Ring' nebula. This is the most famous of the nebulae, and 
is extremely easy to find, as it lies between Beta and Gamma 
Lyrae. In a small telescope it does indeed look like a ring; the 
dark centre is easy to see, but the central star is a difficult object. 

Theta Serpentis. R.A. 18 h 54 m -4, Dec. +4° 09' 

One of the best double stars for a small telescope. The com- 
ponents are almost equal at magnitude 4-1; the p.a. is 103°, and 
the distance 22"-3. The star is easy to find, as it lies almost in a 
line with Theta, Eta and Delta Aquilae. Each component is white. 

Beta Cygni. R.A. 19 h 29 m -3, Dec. +27° 53' 
Beta Cygni (Albireo) is probably the loveliest double star in the 
sky. It is an easy object; the magnitudes are 30 and 5-3, the p.a. 
055°, and the separation 35", so that any small telescope will 
show it. The contrasting colours make it striking; the primary 
is yellow, while the companion is strongly bluish-green. Albireo 
appears the faintest of the five stars which make up the cross of 
Cygnus, but it is in fact a very luminous star lying at a great 
distance from us. 

Chi Cygni. R.A. 19 h 49 m -2, Dec. +32° 49' 
An M-type long-period variable. The range is from magnitude 


4 to 14, and the period 409 days; it is the Mira type. When near 
maximum it is easily visible to the naked eye, and may be com- 
pared with its near neighbour Eta Cygni (magnitude 4). Near 
minimum, a powerful telescope is needed to show it. 

Eta Aquilje. R.A. 19 h 50 m -6, Dec. +0° 55' 
Spectrum GO (peculiar). Eta is a typical Cepheid variable, with 
a range from magnitude 3-7 to 4-5, and a period of 718 days. 
It lies between Delta (magnitude 3-4) and Theta (also 3-4), which 
are useful as comparison stars. 

Messier 27 Vulpecul*. R.A. 19 h 58»-l, Dec. +22° 37' 
The curious galactic 'Dumb-bell' nebula, not far from Gamma 
Sagittal It is a faint object in a small telescope, but is well worth 
looking for. 

Alpha Capricorni. R.A. 20* 15»-8, Dec. -12° 39' 
A naked-eye double; Alpha 1 and Alpha 2 , of magnitudes 3-7 
and 4-3 respectively, are separated by 378". Alpha 1 has a ninth- 
magnitude companion at 45". Alpha 2 is itself a difficult double; 
the companion is of magnitude 11, position angle 158°, distance 
7". Since the faint companion is a close binary, the whole system 
is decidedly complex. 

Alpha Cygni (Deneb). R.A. 20 h 40 m -2, Dec. +45° 09' 
The brightest star of Cygnus. It is of magnitude 1-3, and has a 
peculiar A2-type spectrum. It is an exceptionally luminous star, at 
least 10,000 times as brilliant as the Sun, and is of great interest to 
astrophysicists. Its yellowish colour is well shown by use of a 
low power. 

Gamma Delphini. R.A. 20 h 45 n >0, Dec. +16° 00' 
A wide, easy double. Magnitudes 4, 5; p.a. 270°, distance 10"-4. 
The primary is yellowish, the companion greenish. 

H.IV. 1 Aquarii. R.A. 21 h 02 m l, Dec. -11° 31' 
A bright planetary nebula, known as the Saturn nebula for 


reasons which will be obvious when the object is studied with a 
large aperture. In smaller telescopes the Saturn-like appearance is 
not seen, but nevertheless the nebula is a most interesting object. 
It lies near the fourth-magnitude star Nu Aquarii. 

61 Cygni. R.A. 21 h 05 m -3, Dec. +38° 34' 
An easy binary; magnitudes 5-3, 5-9; p.a. 134°; distance 
25". 61 Cygni is famous as being the first star to have its distance 
measured - by Bessel, in 1838. The system is about 11 light-years 
away. Both components are dwarfs, and the fainter (B) is sus- 
pected to have a large planet associated with it. 

Messier 15 Pegasi. R.A. 21 h 28 m -3, Dec. +12° 01' 

A splendid globular cluster not far from Epsilon Pegasi (magni- 
tude 2-5). A small telescope will show it well. 

Beta Cephei. R.A. 21 h 28 m -2, Dec. +70° 24' 

A third-magnitude star with an eighth-magnitude companion 
at p.a. 250°, distance 13"-7. As it is circumpolar, it makes a useful 
test (for small apertures) which is available on any clear night. 

Messier 39 Cygni. R.A. 21 h 31 m 0, Dec. +48° 17' 

A large open cluster, between Deneb and Alpha Lacertae, well 
seen with low powers. 

Mu Cephei. R.A. 21 h 42 m -4, Dec. +58° 36' 

The 'Garnet Star' of Sir William Herschel. It is a Betelgeuse 
type irregular variable, but since its fluctuations lie between 
magnitudes 4 and 6 it is never brilliant. However, any optical aid 
will bring out its lovely red colour; it has been compared with a 
glowing coal. 

Delta Cephei. R.A. 22 h 27 m -8, Dec. +58° 14' 

The prototype Cepheid. It changes between magnitudes 3-7 and 
4-3 in a period of 5-37 days. Its neighbour Zeta (magnitude 3-6) 
makes a useful comparison star. 


Alpha Piscis Austrini (Fomalhaui). R.A. 22 h 55 m -7, 
Dec.-29° 49' 
This is the southernmost of the first-magnitude stars visible 
from Britain. It can be quite conspicuous from southern England, 
but from northern Scotland it is always extremely low down. It is 
of spectrum A3, and is 13 times as luminous as the Sun. As it lies 
at a distance of only 24 light-years, it is the nearest of the first- 
magnitude stars apart from Sirius, Procyon and Alpha Centauri. 

Beta Pegasi. R.A. 23 h 02 m 0, Dec. +27° 53' 
An M-type variable of the Betelgeuse class. Its range is be- 
tween magnitudes 2-3 and 2-8, and there is a very rough period of 
about five weeks. It is one of the stars making up the Square of 
Pegasus, and good comparisons are Alpha Pegasi (2-6) and 
Gamma (2-9). Beta is strongly orange in hue, and its alterations 
in brightness may be followed with the naked eye. Incidentally, 
it is instructive to select a clear night and then count the number 
of naked-eye stars contained in the Square of Pegasus. There are 
not very many of them ! 

Biographical Notes on Contributors 

H. G. miles, lecturer at the Lanchester College of Technology, 
Coventry, is the Director of the Artificial Satellite Section of 
the British Astronomical Association, and has collaborated 
extensively with scientists in Britain and abroad in connexion 
with tracking the various Earth satellites. 

dr J. g. porter was for many years concerned with the produc- 
tion of the Nautical Almanac, and retired from the Royal 
Greenwich Observatory in 1961; between 1961 and 1962 he 
was carrying out research in the United States. In addition to 
his computing work, he has specialized in the study of comets 
and meteors, and is the author of Comets and Meteor Streams. 
He is a Past President of the British Astronomical Association, 
and a former Director of its Computing Section. For over ten 
years he made monthly broadcasts on astronomical subjects. 

peter j. cattermole is a geologist who took his degree at 
Aberystwyth University. He is an amateur astronomer, 
concerned principally with observations of the Moon; co- 
author of an extensive catalogue of lunar domes. He is a Fellow 
of the Royal Astronomical Society. 

w. e. fox has for some years been Director of the Jupiter Section 
of the British Astronomical Association, and is himself a very 
active observer of the planet ; his observational work is carried 
out from the observatory set up at his home at Newark, in 

henry wildey, f.r.a.s., is Curator of Instruments of the 
British Astronomical Association. He has an international 
reputation as a telescope-maker, and has also carried out an 
extensive programme of observational work. He is former 


Vice-President of the B.A.A., and a Past President of the 
Junior Astronomical Society. 

henry brinton is the author of numerous political works, as 
well as novels. He is also known as a children's science writer, 
and is a frequent broadcaster on sound and television. His 
private observatory at Selsey, in Sussex, is equipped with a 
12|-inch optical reflector as well as a home-made radio 
telescope. He was elected to the Council of the British Astro- 
nomical Association in 1962. 

H. N. d. wright, f.r.a.s. Amateur astronomer who has 
specialized in observing the planet Saturn, though he also 
studies other branches of astronomy - in particular the Sun, 
and occultations of stars by the Moon. He is a council member 

c. A. ronan,, f.r.a.s. Director of the Historical Section 
of the British Astronomical Association, and recognized as a 
leading authority on scientific photography in all fields. He is a 
well-known author, and a frequent broadcaster on sound and 

philip s. laurie is a Senior Experimental Officer at the Royal 
Greenwich Observatory, Herstmonceux, which he joined in 
1935. He supervises the Solar Department, whose principal 
work is the detailed measurement and publication of the 
positions and areas of sunspots. 

Patrick moore is an amateur observer of the Moon and planets. 
He was awarded the Lorimer Gold Medal in 1962. 

Yearbook of Astronomy 1964 

Edited by J. G. Porter Associate Editor Patrick Moore 

This Yearbook has been specially designed 
for the amateur astronomer and, once 
again, the new edition has been completely 
revised. The notes and data have been 
brought up to date for 1964 and a new 
series of articles on various subjects in- 

Two extracts from reviews show how 
enthusiastically the previous editions of the 
Yearbook were received : 

h'oture: 'It succeeds admirably . . . we look 
forward to seeing the Yearbook maintain- 
ing the high standard of this issue for many 
years to come ... a very useful addition* 
to the shelves of any amateur astronomer.' 

TTre Observe. 1 ': 'Spotting the main scars and 
constellations, as well as the planets, is 
made easier with this handbook than any 
other publication I have come across.' 

I6s net 

Q6.'2509'I0 ijjukowly 

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