Practical astronomy with the unaided eye

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TACTICAL
ASTRONOMY

WITH THE UNAIDED EYE

BY

*v

The Rev. HECTOR MACPHERSON

M.A., F.R.A.S., F.R.S.E.

MEMBER OF THE SOCIETE ASTRONOMIQUE DE FRANCE, ETC.

AUTHOR OF "THE ROMANCE OF MODERN ASTRONOMY," "ASTRONOMERS

OF TO-DAY," "A CENTURY'S PROGRESS IN ASTRONOMY"

REVISED EDITION

SJotrfcott attb (BMnbttr^h :

T. C. & E. C. JACK, LTD. | T. NELSON & SONS, LTD.
1919

CONTENTS.

I. Introductory 5

II. The Northern Stars

. 24

III. The Stars of Winter .

. 36

£Y. The Stars op Spring

. 54

V. The Stars op Summer .

66

VI. The Stars of Autumn .

82

VII. The Southern Stars

95

VIII. Sun, Moon, and Planets

101

IX. Astronomical Phenomena

116

Bibliography ....

126

Index

127

PRACTICAL ASTRONOMY.

CHAPTER I.

INTRODUCTORY.

When we cast our eyes to the heavens on
any clear and, by preference, moonless night,
our attention is attracted by apparently in-
numerable points of light, of all degrees of
brightness. These are the stars, which in all
ages have drawn to themselves the attention
of mankind. Mr. E. W. Maunder, in a previ-
ous volume of this series, has shown how man's
attention was first directed to the heavenly
bodies, and how the mere recognition of the
phases of the Moon, the varying positions of the
planets and the seasonal changes of the stars
has developed stage by stage into the science
of astronomy as we know it at the present day.
Perhaps of all the sciences modern as-
tronomy is the most awe-inspiring, the most
wonderful, the most instructive. The aver-
age man reads of the marvels which the
telescope and spectroscope reveal, of the

6 PKACTICAL ASTRONOMY.

great depths and spaces, the rapid velocities,
the eternal working of evolution, and he
wonders. He has little or no knowledge of
the methods used by the astronomers in
ascertaining the '"acts of the science ; and
he is not familiar with the stars or constella-
tions. Let us suppose that there is something
unusual in the astronomical world. The news-
papers are full of the " opposition of Mars."
The average man has read about Mars and he
is anxious to see the planet for himself. The
almanacs tell him that it is in a certain con-
stellation, say, Virgo, and the newspapers
repeat the statements of the almanacs. The
would-be observer of Mars is as puzzled as
ever. He knows nothing of the constellation
Virgo. He does not know where to look for
it, and even if he did, he would probably be
unable to recognise it. He is paying the
penalty for not having made himself ac-
quainted with what we may call the topog-
raphy of the heavens.

Again, let us suppose that a bright comet
is to be seen or that a meteoric shower is
expected from a certain constellation, say,
Leo. The would-be observer is in the same
position as in the case previously mentioned.
His ignorance of the topography of the sky is
at the root of his inability to see the comet
or to witness the meteoric shower.

INTRODUCTORY. 7

So much for the utility of knowing the
names of the various stars and constella-
tions ; but a knowledge of this kind is more
than merely useful. No one can really enter
into what may be called the spirit of astron-
omy without having an acquaintance, how-
ever slight, with the planets and stars in-
dividually. As a contemporary astronomer
has well remarked : " How great an interest
is given to any object by the fact that we
know its name. Take some town children
out into the country and set them to gather
wild flowers : how instantly they ask their
names." It is the same in the case of the
stars. When in a clear night we " consider
the heavens " and behold apparently count-
less points of light, we are confused and over-
whelmed by the number of the stars and
by the complexity of their distribution. One
star appears to be almost the same as an-
other, except for the differences in bright-
ness, and we look away from the sky again
with neither interest nor curiosity. But
if we learn that such and such a star is Al-
debaran, and such and such is Sirius, and
such and such a constellation is Orion, then
our interest in the stars is aroused and as a
result we are desirous of tracing out the star
groups and of identifying the stars themselves.

" But," the would-be astronomer asks at

8 PRACTICAL ASTRONOMY.

this time, " how is it possible for me to learn
the names of the stars and trace the outlines
of the constellations without being taught 1 "
Carlyle in his old age lamented " Why did
not somebody teach me the constellations
and make me at home in the starry heavens ? "
But in reality it is not necessary for anyone
to be taught the constellations. It is best
for everyone to learn them for himself.

When the would-be astronomer begins his
task it may seem almost impossible of attain-
ment, and some of the hints which are given
in astronomical books only make the task
more difficult. For instance, when we are
told to draw imaginary lines through such
and such stars in the Plough, and that these
will lead us to such and such stars in Bootes
and will form triangles and quadrilaterals
with such and such stars in Draco, we feel
baffled with the magnitude of the task. Again,
on some maps and guides to the heavens there
are represented what are known as " the
constellation figures." On such maps we
find the Plough represented by the figure of
a bear covered with stars, Cygnus by a star-
spangled swan, Orion by a human figure
dotted with stars. The stars of all mag-
nitudes are inserted and named, but they are
confused and individually lost through the in-
troduction of the constellation figures. These

INTRODUCTORY. 9

figures of course are of extreme interest to the
historian of astronomy and to the antiquarian.
They throw a flood of light on important
questions connected with the beginnings of
astronomical science, but on star maps in-
tended for the beginner who desires to obtain
a knowledge of the topography of the heavens,
they are utterly out of place.

The best method of acquiring a knowledge
of the stars is to study them as they are, and
to obtain a knowledge of the most important
constellations in the heavens which it is
impossible to mistake. From this it is com-
paratively easy to trace out the other con-
stellations ; to simplify this task by ex-
planation and direction is the aim of the
following pages.

Once the observer has become familiar
with the various constellations and their
seasonal changes a new charm is added to
his interest in the stars. As an able astron-
omer has remarked, the task of learning the
stars " has a charm of its own. The silent
watchers from heaven soon become each a
familiar friend, and to any imaginative mind
the sense that he is treading the same path
as that traversed by the first students of
Nature will have a strange charm."

Our Place in the Universe. — Before enter-
ing on the task of describing the topog-

10 PRACTICAL ASTRONOMY.

raphy of the heavens, it is necessary to
consider briefly our position in the Universe
and the bearing of the position and motions
of our planet on the appearance of the heavens,
and on the apparent motions of Sun, Moon,
planets and stars.

We live on the Earth, a globe almost 8000
miles in diameter. This globe is not, as the
ancient astronomers believed, suspended in
space. It is in ceaseless motion ; it turns
on its axis once in twenty-four hours, and in
addition it revolves round the sun in 365J
days. The mean distance of the Earth from
the Sun is 93,000,000 miles, so the pathway
traversed by our world is about 186,000,000
miles in diameter. In order to travel round
this great orbit in a year, the Earth whirls
through space at the amazing rate of eighteen
miles in one second.

But the Earth does not travel alone. It is
accompanied on its journey by its faithful
satellite the Moon. The Moon revolves round
the Earth in a little over twenty-seven days,
at an average distance of 238,000 miles. Just
as we get our unit of time, a day, from the
rotation of the Earth on its axis, and a year
from the Earth's revolution round the Sun,
we derive our other unit, the month, from the
Moon's revolution round the Earth.

The Earth is not, however, the only body

INTRODUCTORY. 11

which revolves round the Sun. The orb of
day holds sway over a large system of bodies
— planets, comets and meteors. The five
larger planets are very conspicuous and have
been known from prehistoric times — Mercury
and Venus within the orbit of the Earth ;
Mars, Jupiter and Saturn without. In ad-
dition there are two distant planets, Uranus,
almost invisible to the unaided eye, and
Neptune, completely so ; and many small
planets, between the orbits of Mars and
Jupiter, but invisible to the unaided eye
on account of their great distance. There
are also numerous comets and their kindred
bodies, meteors, revolving round the Sun
and coming within the reach of human vision
from time to time.

The Solar System, so far as we know at
present, is a little under 5,000,000,000 miles
in diameter, the orbit of Neptune being the
known boundary. In this system the Earth
is merely one planet among others ; and it
is by no means the largest. It comes fifth
in order of size, being much smaller than
Jupiter, Saturn, Uranus and Neptune, and
slightly larger than Venus, Mars and Mercury.

The Solar System. — The Sun, the central
body of the Solar System, is a huge globe
about 866,000 miles in diameter. In volume
it is one and a quarter millions of times greater

12 PEACTICAL ASTKONOMY.

than that of the Earth, and its mass is 332,000
times that of our planet. The Sun is a great
globe of gaseous matter, at an almost incon-
ceivably high temperature. The glowing en-
velope visible to us — the photosphere — is
merely the outer surface. This surface is
diversified from time to time by the appear-
ance of sun-spots — great holes or cavities in
the photosphere. From these spots it has
been ascertained that the Sun rotates on its
axis in about twenty-five days ; at least this
is the period for the equatorial regions, for
the vast globe does not rotate as a whole.
The spots are not always equally numerous.
They increase and decrease in a period of
about eleven years. This period is called
the solar cycle, and is obeyed by the faculse,
or bright spots on the photosphere, and by
the prominences or red flames which are
projected from the chromosphere, a thin
gaseous envelope surrounding the photo-
sphere. The corona, the outermost append-
age of all, varies in shape according to the
same period. In addition, the variations
of the magnetic needle and of the aurora
on earth have a similar period. The dis-
covery of magnetic fields in sun-spots by the
American astronomer Hale gives us some idea
of the nature of the connection.

The Sun holds sway over a system of bodies

INTRODUCTORY. 13

of varying size and condition. We may di-
vide these into two classes: (1) the planetary,
and (2) the cometary bodies. The planets fall
into three subdivisions : (1) the inner planets ;
(2) the minor planets, or asteroids ; and (3) the
outer planets. In addition, two of the inner
and the four outer planets are centres of sub-
ordinate systems of one or more satellites.

The inner planets are, in order of distance,
Mercury, Venus, the Earth, and Mars. Our
planet is slightly larger than Venus and con-
siderably larger than Mars or Mercury. Venus
and Mercury have no satellites ; our Earth
has one — the Moon — and Mars has two.
Comparatively little is known of Mercury
and Venus. Mercury seems to be a barren,
rocky world, and it is generally accepted
among astronomers that its rotation is per-
formed in eighty-eight days, the same period
as is required for its revolution round the
Sun. One hemisphere, accordingly, experi-
ences everlasting day and the other per-
petual night. Many astronomers accept a
similar conclusion in regard to Venus, but the
evidence is not so strong. The atmosphere
of Venus is very thick and cloud-laden, and
very few of its surface-markings are known.

Mars, on the other hand, rotates on its
axis in about twenty-four hours thirty-seven
minutes. The atmosphere of Mars is con-

14 PRACTICAL ASTRONOMY.

siderably thinner than that of our Earth,
and its surface-markings have been mapped
for two centuries. The disc is diversified
by reddish-ochre and blue-green areas, while
at the poles there are white spots which
wax and wane in accordance with the Mar-
tian seasons. The reddish-ochre regions, from
which the planet takes its ruddy tint, are
known to be deserts, and the blue-green
areas marshy tracts of vegetation, while
the polar caps are composed of snow and ice.
In 1877 Schiaparelli, at Milan, discovered
the remarkable " canal " system which for
the last forty years has attracted so much
attention. The whole surface of Mars is cut
up by a system of straight dark lines, which
vary according to the seasons. Many theories
have been put forward to account for the canal
system. At present the balance of evidence
is in favour of the theory of the late Professor
Lowell of Arizona, based on his study of the
planet for twenty-two years — that the canal
system is artificial and indicates the existence
of intelligent life on our neighbouring world.

Mars appears to represent a later stage in
planetary development than our Earth. The
Moon is at a still later period. Long-con-
tinued study of the Moon has convinced
astronomers that it is practically a dead world.
Professor W. A. Pickering's researches have

INTRODUCTORY. 15

led him to the conclusion that there is a very-
thin atmosphere, and that vegetation of a
low order still exists. But the existence of
animal life is highly improbable. The lunar
rotation is performed in exactly the same
period as its revolution round the Earth.
One hemisphere is continually turned towards
us, and the other side has never been seen.

The asteroids, a group of about 800 tiny
planets, revolve between the orbits of Mars and
Jupiter. The largest, Ceres, is about 400 miles
in diameter ; the smallest are very minute.
A very tiny asteroid, discovered by Max Wolf
early in 1918, has a diameter of only four miles.

The four outer planets — Jupiter, Saturn,
Uranus, and Neptune — are very much larger
than the Earth and its neighbouring worlds.
The largest, Jupiter, is nearly 90,000 miles in
diameter. All four seem to be in a condi-
tion of great internal heat, and it is doubtful
if solid surfaces exist below their heavy cloud-
laden atmospheres. Jupiter has nine satel-
lites— four large and five small ; Saturn ten ;
Uranus four ; and Neptune — so far as is
known — one. In addition, Saturn is encircled
by a wonderful system of rings, composed
of myriads of tiny meteorites revolving so
closely together as to be individually indis-
tinguishable from our world.

A considerable number of comets are known

16 PRACITCAL ASTRONOMY.

to be members of the Solar System, revolving
round the Sun in very elliptical orbits. These
comets are not solid bodies like the planets,
but appear to be collections of loose stones,
surrounded by gaseous matter. Meteors, or
shooting-stars, are believed to be the products
of the dissolution of cometary bodies.

Let us suppose that the Solar System,
which is both absolutely and relatively of
so vast an extent, were co-extensive with the
visible universe — in other words, let us imagine
for the sake of clearness that the Universe
were no larger than the Solar System. It
would be indeed a very large universe, much
larger than we are able to comprehend. The
Sun would rise and set as at present ; it
would ascend to its highest point in summer
and descend to its lowest point in winter.
The Moon would pass through its cycle of
changes in its revolution round the Earth.
The planets would make their periodical ap-
pearances, shining brilliantly on an inky black
sky. Usually there would be some object
visible in this black sky ; on moonless nights
one or two planets would probably be seen,
but there would be evenings on which the
heavens would be absolutely black. For
there would be no stars.

Thus by imagining the heavens without
stars, we are enabled at once to assign to the

(2,015)

INTRODUCTORY. 17

stars their true position in the order of nature.
The stars are luminaries far outside of the
Solar System ; the stars, in fact, are not worlds
in any way analogous to the planets ; they are
themselves suns similar to the central body
of the Solar System. It is true that when
we see a planet on the background of stars
it appears much more brilliant. Jupiter, for
instance, shines many times more brightly
than Sirius, the brightest of the stars ; and
yet Jupiter in comparison with even the
faintest star which we see twinkling in the
field of the telescope is utterly insignificant.
It belongs altogether to an inferior order of
bodies ; it is merely the attendant of a star.
Thus we see that one effect of the great dis-
tance of the stars is to make them seem very
insignificant bodies.

Another effect of their distance is that their
motions are to the ordinary observer abso-
lutely imperceptible. One of the great truths
of modern astronomy is that the so-called
" fixed " stars are in motion in various direc-
tions and with different velocities ; but so
great is their distance that these motions can
only be noted after the lapse of many years,
with the aid of powerful instruments and
exact measurements. Were Homer or Hesiod
or the author of the Book of Job alive to-day,
they would see the same constellations and

(2,015) 2

18 PRACTICAL ASTRONOMY.

stars with which they were familiar. They
would behold apparently unchanged the
*' bands " of Orion and the Pleiades and
" the Bear with her train."

Thus to us the stars are the background of
the Solar System — the setting to the drama
of the planetary motions. And as such the
stars were treated for many years. They were
observed mainly as convenient reference-
points for the observation of the positions
of the Moon and planets. Since the days of
Sir William Herschel, however, the stars have
been observed and studied for their own sake.

The stars then are the distant background
of the Solar System. Thus when we read in
astronomical almanacs or in the newspaper
press that " Mars is in Aries " or " Jupiter is
in Taurus," it is necessary for us to remember
that seen from the Earth, Mars is in the same
line of vision as the stars in the constellation
Aries ; that the constellation Taurus is the
background against which Jupiter is seen.

We must also bear in mind that the stars
are not a real background, but only an ap-
parent one. The constellation Taurus, for
instance, is not a collection of bodies all at
the same distance from the Solar System.
Some of the stars in the constellation form
connected groups and systems, but the con-
stellation is not necessarily a unity. In

INTRODUCTORY. 19

other words, the stars are at different dis-
tances. Sirius, for instance, the brightest
star in the sky, is much closer to the Earth
than Kigel in the neighbouring constellation.

The stars are at various distances. To
make this clear, a simple illustration may be
given. Two stars, let us say of equal bright-
ness, appear close together in the heavens.
They may form a connected system, but not
necessarily. One may be much closer to the
Solar System than the other, and they may
appear close together merely because they
happen to lie in the same line of vision. It is
quite a mistake to suppose that the brightest
stars are necessarily the nearest. Sometimes
they are so, sometimes they are not. For
instance, an insignificant star of the fifth
magnitude in the constellation Cygnus is
nearer to the Earth than Sirius, the brightest
star in the sky.

Distance of the Stars. — Something remains
to be said of the distance and magni-
tude of the stars. We have seen that the
diameter of the Solar System is a little under
5,000,000,000 (five thousand million) miles.
The principle of the measurement of star-
distance has been explained by Mr. Maunder
in another volume of this series, and it is only
necessary to give one or two examples of the
distances of the stars. The nearest star is

20 PRACTICAL ASTRONOMY.

only visible in the southern hemisphere. It
is the brightest star of the constellation Cen-
taurus and is known as Alpha Centauri, and
the distance of this orb is about twenty-five
billions of miles. It is almost impossible to
realise this vast distance, but an idea may be
gained from consideration of the fact that if
the distance from the Sun to Neptune, the
most distant planet of the Solar System, were
represented by 10 feet, the nearest star would
be fourteen miles away. The great distance
of the stars may be better realised in another
way. The rays of light, which travel from
the Moon to the Earth in a second and a half,
with a velocity of 186,000 miles per second,
cross the diameter of the Solar System in
eight hours. Four years are required for
light to travel from the nearest star.

Magnitudes of the Stars. — The stars, as we
have seen, are situated at all distances from
the Solar System, and probably they are
of all sizes. Yet their apparent brilliance
does not on the whole depend on distance or
size alone, but on both. One bright star
may be comparatively near and of moderate
size, another may be very distant and of im-
mense dimensions. The stars are divided
into magnitudes according to their apparent
brightness ; and six magnitudes of stars are
within reach of the unaided eye. There are

INTRODUCTORY. 21

about twenty stars of the first magnitude and
sixty of the second. Some of the constella-
tions, as will be explained, are very rich in
bright stars, others very poor.

The brightest stars have proper names.
Thus the brightest star of Canis Major is
known as Sirius, and the brightest star of
Taurus is known as Aldebaran. These proper
names were given to the stars by the early
astronomers, Greek and Arabian. When the
stars came to be catalogued and charted it
was necessary to designate them individually.
Accordingly the brighter stars in each constel-
lation are known by the letters of the Greek
alphabet. Thus Aldebaran is also Alpha
Tauri (literally Alpha of Taurus, " Tauri "
being the Latin genitive), Sirius is Alpha
Canis Ma j oris. When the Greek letters be-
come exhausted, numbers are used.

The Stellar Universe. — Just as the Earth
and the other planets form a system of worlds
revolving round the Sun, so the Sun and the
other stars also form a connected system on
a much vaster scale. While the planets are
separated by millions of miles, the distances
between the individual stars are to be
reckoned by billions.

Much information has been collected con-
cerning individual stars — their distances and
masses — and concerning double and variable

22 PRACTICAL ASTRONOMY.

stars. But two important generalisations
stand out clearly. The stars are aggregated
towards the Milky Way or Galaxy. If we
compare the Stellar System to a great globe,
the Galaxy may be likened to its equator.
There is a progressive increase in the number
of stars as the Galaxy is approached, and the
galactic region seems to be both a region of
greater condensation and of greater extension in
the line of sight. Some of the distant star-clouds
of the Galaxy are so far away that light requires
thousands of years to travel to the Earth.

Another important generalisation has been
established in recent years by the researches
of Kapteyn, Eddington, Dyson and others.
The motions of the great mass of the stars —
^s far as is at present known — are not at
random ; there is a drift of the stars in two
well-defined directions. Various hypotheses
have been put forward to account for this, but
no satisfactory conclusion has yet been reached.
One point is clear — there is no " central sun "
among the stars : the Stellar System is not
analogous to the Solar System. Elammarion,
in one of his happy illustrations, compares the
Solar System to an absolute monarchy with the
Sun as despot, and the system of the stars to a
federal republic with no dominating authority.

It has been computed that there are in the
Stellar System about 500,000,000 stars, and

INTRODUCTORY. 23

several thousands of gaseous nebulae ; but,
nevertheless, it appears to be strictly limited
in extent. Like the Solar System, this greater
Stellar System seems to be merely one among
others. Recent research makes it probable that
some of the isolated star-clusters and many of
the spiral nebulae are external, though prob-
ably smaller and perhaps dependent, systems
plunged at vast distances in space. It has
been computed that the cluster in Hercules,
one of the nearest, is situated at a distance so
great that light requires 100,000 years to travel.
We are confronted then with an ascending
scale of world-systems. First of all, we have
the little terrestrial system — the Earth and
Moon — and other satellite systems within the
greater Solar System ; secondly, the Solar
System is merely one of millions of other
systems, components of the greater Stellar
System ; thirdly, the Stellar System — vast,
almost infinitely vast in extent though it be
— appears to be but one of a number of similar
systems scattered throughout the infinite ex-
tent of space. The human mind is unable to
conceive this apparently endless profusion of
suns and systems and systems of systems. We
pause awe-stricken before what Shelley a century
ago called

" This interminable wilderness
Of worlds, at whose immensity
Even soaring fancy staggers."

24 PRACTICAL ASTRONOMY.

We are face to face with infinity — the eternal,
the illimitable, the unthinkable. In the words
of the poet Richter, " The spirit of man acheth
with this infinity " ; for " end is there none
to the Universe of God. Lo ! also there is
no beginning."

CHAPTER II.

THE NORTHERN STARS.

The positions of the stars in the sky are sub-
ject to two periodical changes — the hourly
change and the seasonal change. The former
is due to the rotation of the Earth on its axis
and the latter is due to its revolution round
the Sun. Even the casual observer can see
that the stars rise and set like the Sun and
that different stars are visible at different
seasons.

Owing to the rotation of the Earth on its
axis the entire star-sphere appears to move
round our world once in twenty-four hours ;
and owing to the revolution of the Earth
round the Sun, the orb of day appears to move
among the stars, or rather, the stars appear
to drift westward into the sunset, rising and
setting four minutes earlier each night.

The Earth rotates on an axis which is

THE NORTHERN STARS. 25

inclined to the plane or level of the terrestrial
orbit round the Sun by about sixty-seven
degrees, and to the perpendicular by about
twenty- three degrees. The result is that some
stars rise and set like the Sun, others are never
to be seen, while others again neither rise nor
set, but seem to circle round a fixed point in
the sky, and are continually visible whenever
the sky is clear and the Sun absent. In a
survey of the heavens, it is wise to commence
with the stars which are continually visible —
the circumpolar stars of the northern hemi-
sphere.

The Plough. — The axis of the Earth points
to a part of the heavens very close to a bright
star of the second magnitude known as the
Pole Star, which remains practically stationary
in the heavens. But the Pole Star is not the
most suitable object from which to commence
a study of the circumpolar stars. There is
no question that the large constellation of
Ursa Major, or the Great Bear — or a part of
it — is the conspicuous object of the northern
heavens. No one can mistake the seven stars
known variously as the Plough, Charles's
Wain and — in America — the Dipper. These
stars have been noted and observed from the
earliest ages ; they are referred to by Homer
and Hesiod and in the Book of Job.

The Plough is seen to best advantage in

26 PRACTICAL ASTRONOMY.

autumn, when it is due north and compara-
tively low down in the heavens ; there can
then be no difficulty in identifying the group.
The northern heavens are not especially rich
in bright stars, and in the autumn evenings
the Plough is visible either slightly tilted to
the north-west, due north, or slightly tilted
to the north-east, according to the hour of
the night or the time of the season. For
instance, at ten o'clock in the beginning of

Fig. 1.— The Plough.

October the Plough is directly north, a month
later at the same hour it is slightly tilted to
the north-east ; but it is unnecessary here to
mention the various days and hours on which
the Plough is to be seen in different positions.
Once the configuration of the constellation is
implanted in the mind, there will be no diffi-
culty in picking it out, whatever its position.

In the winter evenings, generally speaking,
the Plough is in the north-east ascending in

THE NORTHERN STARS. 27

the heavens. As the hours pass on during
the same evening, or as the season progresses
at the same hour, the Plough rises higher
and higher in the heavens until in spring it
is practically in the zenith in the hours fitted
for observation. This is the season when it
is most difficult to recognise the Plough. If,
however, we are familiar with it before, it
is quite easy to identify the well-known figure
high in the sky. In summer, the Plough is
to be seen in the north-west, descending as
the season advances.

On the whole it may safely be said that the
autumn is the best season for a beginner, who
knows nothing of the constellations and has
never seen the Plough, to commence his
studies. Obvious at all times, the Plough is
absolutely unmistakable in the autumn even-
ings. There are seven stars in the constella-
tion, six of which are, roughly speaking, of
the second magnitude and one of the fourth.
Proceeding from the front of the Ploughshare
backwards to the handle, the stars are desig-
nated by the first seven letters of the Greek
alphabet — Alpha, Beta, Gamma, Delta, Ep-
silon, Zeta, and Eta. They are also known
by Arabic names. Alpha is " Dubhe," Beta
is "Merak," Gamma is " Phecda," Delta is
"Megrez," Epsilon is " Alioth," Zeta is
"Mizar," and Eta is " Alkaid " or " Benet-

28 PEACTICAL ASTRONOMY.

nasch." Of these names, only the sixth,
Mizar, is commonly used.

Two of the stars in the Plough call for special
mention, Delta and Zeta. Delta is generally
believed to have been at one time of the second
magnitude, whereas it is now of the fourth,
so it would seem to have decreased in brilliance.
Zeta, generally known as Mizar, is a remark-
able star. A keen eye can detect the fact
that it is double, or rather that there is a faint
companion star near. This little star is known
as Alcor, and in the binocular the two make a
striking spectacle. With a moderate tele-
scope Mizar is seen to be itself double.

The Plough is only part of the constellation
Ursa Major, but it is much the more conspicu-
ous part. The remaining stars of the con-
stellation are much fainter and much more
difficult to trace.

The Pole Star. — Alpha and Beta of Ursa
Major are known as " The Pointers," because
a straight line joining these two stars points
directly to the Pole Star. Once these two
stars are known, it is impossible to mistake
the Pole Star. It is noticeable as being the
next conspicuous star in the line with the
Pointers. As its name indicates, the Pole
Star approximately marks the point in the
heavens to which the Earth's axis points.
To an observer at the North Pole, the Pole

THE NORTHERN STARS. 29

Star would appear almost exactly overhead ;
to an observer at the equator, it would seem
almost exactly on the horizon. In our lati-
tudes, the altitude of the Pole Star above the
horizon varies with the latitude of the place
from which it is observed. To the ordinary
observer, the star seems stationary in the
heavens, the one point around which the
other stars describe circles. In reality its
position does not exactly coincide with the
celestial Pole ; it actually describes a very
small circle, and there are several stars nearer
to the Pole, which are practically invisible
without the aid of a binocular — the chief of
these being Lambda of Ursa Minor, which is
just visible to the unaided eye.

The Pole Star is the chief star of Ursa Minor
or the Little Bear, and is also known as Alpha
Ursae Minoris. The constellation Ursa Minor,
like the more conspicuous Ursa Major, has
seven principal stars. Proceeding in a curve
from the Pole Star these are Delta, Epsilon,
Zeta, and Beta ; while Gamma and Eta form
a square with Beta and Zeta. Beta and
Gamma are the only noticeable stars of the
constellation except the Pole Star.

Cassiopeia. — Once the Plough and the
Pole Star have been identified, the task of
learning the arrangement of the northern
stars is much simplified. If we keep the

30 PEACTICAL ASTEONOMY.

Plough and the Pole Star in view it is easy
to identify another notable constellation. On
the exactly opposite side of the Pole Star
from the Plough and at about the same dis-
tance is a star-group almost as conspicuous,
though smaller than the Plough itself. This
is Cassiopeia or the Lady in the Chair. The
shape is easily remembered ; it is like the
letter W. In the evenings of spring-time,
when the Plough is almost overhead, Cas-
siopeia is visible low down
in the north. It is then to
€ # be seen to the best advan-

•K tage and its W-shape is

h t #0 mos^ obvious. In summer,
^m when the Plough is de-

#»x scending to the north-west,
„ rt _ f . we see Cassiopeia ascend-

Fig. 2. — Cassiopeia. . , . \. A T

mg in the north-east. In
autumn, when the Plough is low down in
the north, Cassiopeia is almost exactly over-
head ; and in winter, when the Plough is
ascending in the north-east, Cassiopeia is
descending in the north-west. Small though
it is in extent, Cassiopeia is one of the
most prominent constellations in the sky
on account of the brightness of its stars and
its symmetrical shape. Beginning at the
right-hand corner of the W-shaped figure,
the five chief stars are Beta, Alpha, Gamma,

THE NORTHEKN STARS. 31

Delta, and Epsilon. Beta, Alpha, and Gamma
are of the second magnitude, and Delta and
Epsilon are of the third. Kappa, though
faint — of the fourth magnitude — is prominent
by reason of its position. It forms a trapezium
with Beta, Alpha, and Gamma. Another faint
star which is easily identified by reason of its
position is Iota, which is in a straight line with
Delta and Epsilon.

The constellation is one of the richest in the
heavens, and in this it differs from its com-
panion star-group, the Plough. Ursa Major
is situated in a barren portion of the sky.
Cassiopeia is fully immersed in the stream of
the Milky Way or Galaxy. The Milky Way
is one of the best-known celestial phenomena.
As Mr. Maunder has explained in a previous
volume of this series, the Milky Way is the
" foundation of the celestial building." It
is the ground-plan of the Universe. It is
nothing more nor less than the region of the
heavens in which the stars are most closely
crowded together. To the unaided eye it
presents the appearance of a belt of milky
light across the sky ; and in this belt, not at
the broadest, but at one of its brightest parts,
the chief stars of Cassiopeia are immersed.
To the observer with a binocular, Cassiopeia
is a particularly interesting field for observa-
tion. The star Gamma is the centre of one

32 PRACTICAL ASTRONOMY.

of the most remarkable regions in the heavens
in regard to the symmetrical arrangement of
the stars ; it is also very crowded.

The constellation is also famous in the
history of astronomy owing to the fact that
the most brilliant temporary star which has
been recorded shone out near Kappa in August
1572. This star was particularly studied by
the famous astronomer Tycho Brahe, who,
although he did not discover it, observed it
so patiently and systematically and left so
complete an account of its variations that it
has always been known as " Tycho's Star."
One evening in November 1572 the astronomer,
on casting his glance upwards, was astounded
to notice the familiar appearance of Cassiopeia
completely changed by the presence of a new
and brilliant star which far outshone the other
stars in the constellation. When first seen by
Tycho it was as bright as Jupiter, and when
it reached its maximum it was equal to Venus
in brilliancy, being visible in full daylight.
Steadily declining, it ceased to be visible to
the unaided eye a year and a half after its
appearance.

Capella and Vega. — Having identified the
Plough, the Pole Star and Cassiopeia, it is
comparatively easy for the observer to find
the other important northern stars. As al-
ready mentioned, the Plough and Cassiopeia

THE NORTHERN STARS. 33

are on opposite sides of the Pole Star. There
are two stars, also on opposite sides of the
Pole, which are useful guiding stars not only
for the northern heavens but also for the stars
which rise and set. On account of their
brilliance, Capella (Alpha Aurigae) and Vega
(Alpha Lyrae) cannot be mistaken ; and al-
though these are — at least in Scotland — cir-
cumpolar stars visible all the year round,
Auriga and Lyra cannot properly be described
as circumpolar constellations. Capella is the
prominent star of the first magnitude between
Cassiopeia and the Plough. In the autumn,
when the Plough is due north and Cassiopeia
nearly in the zenith, Capella is ascending in
the north-east. In winter, when the Plough
is ascending in the north-east and Cassiopeia
descending in the north-west, Capella is to
be seen almost overhead, while Vega is prac-
tically lost in the haze of the horizon. In
spring, when the Plough is nearly overhead
and Cassiopeia low down in the north, Capella
is descending in the north-west and Vega
ascending in the north-east. In summer,
when the Plough is descending in the north-
west and Cassiopeia ascending in the north-
east, Vega is nearly overhead, while Capella
is practically lost in the haze of the horizon.

Vega and Capella will be more fully de-
scribed in the chapters on the summer and

(2,015) 3

34 PRACTICAL ASTRONOMY.

winter constellations respectively ; but it is
essential that these two stars should be known
soon after the Plough and Cassiopeia.

Cepheus. — There are other two northern con-
stellations, less conspicuous than those men-
tioned, which it is well to identify. These are
Cepheus and Draco. The former constellation
adjoins Cassiopeia. When Cassiopeia is low
down in the north Cepheus is above Cassiopeia
to the right, and practically immersed in the
stream of the Milky Way.

The stars Alpha, Beta, Iota and Zeta form
a well-marked trapezium. All four are of the
third magnitude. Within the trapezium and
nearly in the centre is Xi Cephei, of the fifth
magnitude. Gamma Cephei forms a triangle
with Iota and Beta ; it is of the third mag-
nitude and comparatively close to the Pole
Star, with which it is in line. Another much
smaller triangle is formed by Zeta, Epsilon
and Delta. Delta is a variable star — the
brightest of the important and numerous
class known as " Cepheids." It varies from
the third magnitude to the fourth in 5 days
8 hours 7 minutes 40 seconds. Mu Cephei, of
the fourth magnitude, lies between Alpha and
Zeta, below an imaginary line joining them.
It is probably the reddest star visible to the
unaided eye in the northern hemisphere, and
was named by Sir William Herschel " the

THE NORTHERN STARS. 35

garnet star." Seen in the binocular, Mu
Cephei is a very striking and beautiful object.

Draco is one of the most difficult constella-
tions to follow. It adjoins Cepheus and winds
along the barren reaches of the sky near Ursa
Minor, and ends in a line of stars parallel to
the Plough — Alpha, of the third magnitude,
is on a line with Zeta Ursae Ma j oris (Mizar),
Lambda is on line with Alpha Ursae Majoris ;
while Kappa is the star between Alpha and
Lambda. The constellation coils round the
sky until it joins Cepheus ; then it curves
round again and terminates in three bright
stars Xi, Beta and Gamma near the bound-
aries of the constellation Hercules. These
three stars with Iota Herculis form a diamond-
shaped figure.

There are other constellations partly cir-
cumpolar — Cygnus, Perseus and Andromeda,
but these are practically invisible at certain
periods and will be discussed among the stars
of the respective seasons.

We have now completed a survey of the
northern stars which are visible all the night
and all the year round. Beginning with the
Plough, the observer will recognise the Pole
Star and Cassiopeia, and by means of these
he will identify Capella and Vega, the two
watchers of the northern heavens. There is
something awe-inspiring in contemplating the

36 PRACTICAL ASTRONOMY.

ceaseless revolution of these stars, and this
feeling is not diminished by the recollection
that the motion we are watching is that of
our own world projected on the sphere. As
an able writer has expressed it : " To watch
these northern constellations as they follow
each other in regular ceaseless procession
round the Pole is one of the most impressive
spectacles to a mind capable of realising the
actual significance of what is seen. We are
spectators of the movement of one of Nature's
machines, the vastness of the scale of which
and the absolutely perfect smoothness and
regularity of whose working so utterly dwarf
the mightiest work accomplished by man."

CHAPTER III.

THE STARS OF WINTER.

In the previous chapter a description was
given of what are known as the circumpolar
stars — those stars in the northern heavens
which are situated so close to the Pole that
they do not rise nor set, but circle ceaselessly
round. They are to be seen every clear night,
in positions varying with the changing seasons.
The majority of the stars, however, are not
thus situated. They have their seasons of

THE STARS OF WINTER. 37

visibility and invisibility, of favourable and
unfavourable positions, depending on two
factors — their apparent distance from the
Pole and their position with respect to the
Sun. As mentioned in the previous chapter,
as the distance of a star from the Pole in-
creases, the circle which it describes grows
wider and wider. Some constellations, such
as Perseus, Andromeda and Auriga, are partly
circumpolar partly seasonal. The circles
which they describe only pass very slightly
below the northern horizon. Other constella-
tions, such as Gemim and Bootes, pass below
the horizon for a slightly longer period ; but
such groups always rise in the north-east and
set in the north-west. Other groups farther
from the Pole, such as Orion, rise almost due
east and set almost due west ; while others
again merely ascend a little distance above
the southern horizon, rising in the south-east
and setting in the south-west.

Owing to the apparent motion of the Sun
among the stars, or, as it appears to us, the
apparent drifting of the stars into the sunset
twilight, these stars which rise and set have
their particular seasons of visibility. The
nearer the constellation is to the Pole the
longer its period of visibility. For instance,
Auriga only disappears from view for a short
time. The farther a constellation is from the

38 PKACTICAL ASTKONOMY.

Pole, the shorter the period during which it
is visible. This is the case with Canis Major,
Lepus, Scorpio and other groups which never
rise far above the southern horizon.

Even those stars which are visible almost
all the year round are seen to most advantage
in certain seasons ; and the easiest way to
learn the various star groups is to discuss them
season by season.

We begin with the stars of winter, for two
chief reasons. In the first place, the winter-
time is the season when astronomical ob-
servation is easiest. The long dark evenings
are the most favourable for the study of the
heavens. In the second place, the winter
constellations are the most brilliant and most
easily identified. It is a curious fact that the
stars visible in the winter months are far more
beautiful and striking than those to be seen
in spring, summer or autumn. As Flammarion
has truly remarked : " Nature everywhere
establishes harmonious compensation, and
whilst it darkens our short and frosty days it
gives us long nights enriched with the wealth-
iest creations of the heavens."

Orion. — In some guides to the stars direc-
tions are given to identify the brilliant winter
stars by means of lines drawn from the Plough
or Cassiopeia. In reality no such method is
necessary ; for Orion, the leader of the winter

THE STARS OF WINTER. 39

constellations, is the most brilliant of all the
star-groups, and is always visible at a con-
venient altitude for observation. It rises al-
most due east, culminates midway between
the horizon and the zenith, and sets almost
due west. Once seen, Orion can never be
forgotten. In the early evening in November
and December, it is visible rising in the south-
east ; later in the season it reaches the me-
ridian, or point due south. In
February and March it is de- ^
scending in the south-west. ™ •

A large proportion of people,
who have no particular interest ^~

in astronomy, are familiar with #^€
Orion. The figure is easily re-
membered. An irregular quad- ©«,
rilateral is formed by the four £ ®3
bright stars, Alpha, Gamma, K
Beta and Kappa. In the centre FlG' 3--°BION-
of this quadrilateral are three stars almost
equally bright, nearly in a straight line slant-
ing downwards. These are Delta, Epsilon
and Zeta.

Of these seven stars two, Alpha and Beta,
are of the first magnitude, and five, Gamma,
Kappa, Delta, Epsilon and Zeta, of the second.
Alpha, at the north-east or top left-hand corner
of the quadrilateral, is more familiarly known
by its Arabic name Betelgeux. It is a very

40 PRACTICAL ASTRONOMY.

conspicuous object, shining with a red light
which contrasts with the bluish- white radiance
of Rigel. Generally, Betelgeux is inferior in
brilliance to Beta Orionis, more commonly
known as Rigel, the star in the south-west,
or the bottom right-hand, corner of the quad-
rilateral ; but at times it increases in bright-
ness and outshines Rigel. Its variations are
irregular, but easily followed. It is generally
believed to have been brighter than Rigel in
1603, when the Greek letters were assigned to
the individual stars. At that date it was
designated Alpha, indicating that it was
then the chief star of the constellation.

These two stars, Betelgeux and Rigel, have
been much studied by astronomers. Both are
so far distant from the Earth that it cannot
be said that the attempts to measure their
distance have met with success. Approximate
measurements, however, have been made.
Betelgeux is at least over 20,000 times more
massive than the Sun. It is, as already men-
tioned, a red star, as its atmosphere is much
heavier than that of our orb of day. As the
subject of spectroscopic astronomy is dealt
with in another volume of this series, it is
unnecessary to mention the methods by which
astronomers have reached their conclusions
concerning these stars. Betelgeux is, as al-
ready mentioned, a variable star ; and vari-

THE STABS OF WINTER. 41

able stars of this particular type are generally-
red in colour.

Rigel, on the other hand, is bluish-white in
colour, shining with a clear light. Its only
points of resemblance to Betelgeux are its
immense distance and enormous size. Its
distance cannot be measured, but astronomers
have calculated the minimum distance at
which it can be placed. It is placed, even on
the minimum estimate, at a distance so vast
that light, which travels from the Sun in 8
minutes and from the boundaries of the Solar
System in 4 hours, requires no less than 307
years to cross the mighty void. It must be a sun
of enormous size, probably one of the greatest
bodies in the entire Universe ; its mass is at least
37,000 times that of the Sun, and, as we know,
the Sun is inconceivably larger than the Earth.

Gamma Orionis, in the north-west or top
right-hand corner of the quadrilateral, is fre-
quently known by its Arabic name Bellatrix.
At the south-east corner of the figure is Kappa,
also of the second magnitude.

The most famous object in the constellation
is, however, the Great Nebula in Orion. It
surrounds Theta Orionis, the middle star of
the " Sword of Orion," which consists of three
faint stars in a straight line with Epsilon, the
middle star of the belt. On a clear night a
keen eye can detect a haziness about Theta

42 PKACTICAL ASTRONOMY.

which a binocular shows to be a cloud of
misty light. Even in a small telescope it is
a striking spectacle. The haziness expands
into a magnificent cloud-like object, and its
apparent size increases as the telescope em-
ployed becomes larger. The nebula is a
gigantic mass of glowing gas, thousands of
times larger than the Solar System. Photog-
raphy has shown the nebula to be vastly
more, extended than it appears to be when
studied with the telescope ; indeed the whole
constellation has been ascertained to be
wrapped in nebulous haze.

Orion, as the most conspicuous of the con-
stellations, has been known from the earliest
ages and is referred to by the early writers.
Homer refers to Orion, while we are all familiar
with the well-known passage in the Book of
Job, " Canst thou loose the bands of Orion ? "

Canis Major and Canis Minor. — Orion is
the index-constellation of the winter star-
groups in the southern aspect of the heavens.
Betelgeux forms a very conspicuous equilateral
triangle with two other bright stars, Sirius in
Canis Major and Procyon in Canis Minor.
As the old rhyme has it :

" Let Procyon join to Betelgeux and pass a line afar,
To reach the point where Sirius glows, the most conspicuous

star,
Then will the eye delighted view a figure fine and vast,
Its span is equilateral, triangular its cast."

THE STAES OF WINTER. 43

The great triangle is one of the most notice-
able configurations in the entire heavens ;
its striking appearance being due to the bril-
liance of the three stars composing it and to
the dearth of stars within. Procyon, a star
of the first magnitude, is the chief star — Alpha
— of Canis Minor or the Little Dog. It is the
only conspicuous star in an inconspicuous
constellation. More striking in its appearance
is Canis Major or the Great Dog. This group
is famous as containing Sirius — Alpha Canis
Majoris — the brightest star in the sky. Sirius
is never to be seen very high in the heavens
in these latitudes, rising in the south-east and
setting in the south-west. The " Dog Star "
has been termed " the monarch of the skies,"
and so far as mere brilliance is concerned fully
merits the title. Much of its brilliance, how-
ever, is due to the fact that it is comparatively
one of our nearer neighbours in space. Light
requires eight years to reach us from the Dog
Star, as compared with hundreds of years from
Betelgeux and Rigel. Therefore, although
Sirius is probably considerably larger than our
Sun, it is relatively a small star in comparison
with other orbs which appear its inferiors on
account of their greater distance. Sirius is a
well-known double star, but the satellite can
only be seen in powerful telescopes.

Taurus. — Higher in the sky than Orion are

44 PKACTICAL ASTRONOMY.

two brilliant constellations, Taurus and Gremini.
It is impossible to mistake the two groups.
Taurus is north-west of Orion, Gremini north-
east. Taurus is the second of the twelve con-
stellations of the Zodiac, through which the
Sun moves on its apparent path round the
Earth, while Gremini is the third. Of the
two Taurus is the more famous, as it contains
the two well-known star-clusters, the Hyades

v

•*

Fig 4.— Taurus.

#>

and the Pleiades. The former is a group of
five stars arranged like the letter V. The
brightest star of the Hyades, and indeed of
the constellation, is Aldebaran or Alpha
Tauri, which marks the upper left hand of
the figure. Epsilon, of the fourth magnitude,
marks the upper right hand, and Gamma, also
of the fourth magnitude, the angle. Aldebaran
is by far the most conspicuous star ; it is of a
bright red colour and indeed closely resembles

THE STAES OF WINTER. 45

Betelgeux in the neighbouring constellation.
The distance of Aldebaran has been measured
with some approach to certainty, and its mass
is believed to be about two hundred times
that of the Sun.

The Pleiades. — Higher in the sky than Alde-
baran and the Hyades, and on the right-
hand side of these stars, is the most famous
star-cluster in the entire heavens — the Pleiades.
Like the Plough and Orion, this cluster has
attracted the attention of man from prehistoric
times. " Canst thou bind the cluster of the
Pleiades ? " asks the Creator of Job in that
Book of the Bible.* Hesiod too says of the
Pleiades,

" There is a time when forty days they lie
And forty nights, concealed from human eye,"

referring to their invisibility when the Sun is
passing through Taurus.

The Pleiades begin to appear in the late
evenings of autumn, above the eastern horizon.
At this season we, like Tennyson's hero of
Lochsley Hall, behold

"... the Pleiades rising through the mellow shade
Glittering like a swarm of fire-flies tangled in a silver braid."

The name " Pleiades " is probably derived
from the Greek " Pleiones," many or full.
The stars are closely packed together. Six

* Revised Version.

46 PRACTICAL ASTRONOMY.

stars, the brightest of which is Alcyone, or
Eta Tauri, are visible to a person of average
sight, but a very keen eye will discern as many
as twelve or fourteen. The binocular changes
the entire aspect of the cluster, revealing many
more stars, while in the telescope many hun-
dreds may be seen. Since the invention of
the telescope the cluster has received its full
share of attention. The photographic plate
has shown it to consist of thousands of stars ;
and not the least interesting of the revelations
of photography has been the discovery that
the group of the Pleiades is not a cluster pure
and simple, but that the stars composing it
are embedded in nebulae, masses of incan-
descent gas. The cluster seems to be in a
chaotic condition, and the stars composing it
are generally considered to be at an earlier
stage of evolution than our own Sun.

Gemini — Next to Taurus, and to the left
of Orion, is the constellation Gemini or the
Twins. Gemini is chiefly notable for the two
bright stars, Castor and Pollux, on the eastern
boundary of the constellation. Castor is des-
ignated as Alpha Geminorum and Pollux as
Beta Geminorum. Here we have a case
similar to that of Alpha and Beta Orionis ;
Pollux is brighter than Castor. It is generally
believed that Castor has decreased in brilliance
since the stars received their Greek letters.

THE STARS OF WINTER. 47

Castor is a double star, but is not within the
reach of the binocular. On the right-hand
side of the constellation is a square formed by
four stars Epsilon, Mu, Gamma and Zeta.
Epsilon and Mu are of the third magnitude
and Gamma of the second ; while Zeta is a
well-known variable, fluctuating from the
third to the fourth magnitude in 10 days 3
hours. It can be easily followed with the un-
aided eye or binocular. Zeta forms an equi-
lateral triangle with other two stars, Delta of
the third magnitude and Lambda of the fourth.
Finally, close to Mu is a noticeable star Eta, of
the third magnitude although slightly variable.

Lepus and Eridanus. — Returning to Orion,
it is well to note the inconspicuous constella-
tions close to it, Lepus and Eridanus. Lepus
— the Hare — is exactly underneath the magnifi-
cent star group. There is nothing remarkable
about this constellation ; its four chief stars,
Alpha and Beta of the third magnitude and
Gamma and Delta of the fourth, form the
corners of an irregular quadrilateral. Eridanus
is a much less compact constellation. It
straggles from close to Orion to the boundaries
of Cetus, and then curves downwards into the
southern hemisphere. Beta Eridani, of the
third magnitude, can be easily identified from
its proximity to Rigel.

Auriga. — A survey of the winter constella-

48 PKACTICAL ASTRONOMY.

tions is incomplete without reference to one
of the most remarkable of all, namely Auriga.
Starting from Orion, the guiding constellation
of winter, it is easy to recognise Auriga. Above'
Orion, as we have seen, are Taurus and Gemini,
the bright stars of which are on either side of
the space immediately above Orion. Above
these two, and therefore directly above Orion
and almost in the zenith, is Auriga. This
group, which, as mentioned in the preceding
chapter, is almost a circumpolar constellation,
is of the shape of an irregular pentagon, with
one of its sides much shorter than the rest.
The stars forming the corners of the figure are
Alpha or Capella, Beta, Theta, Iota and Ep-
silon. Capella is of the first magnitude and
one of the most brilliant of all the stars. It
is a star of the same type as our Sun, only
very much larger and more massive ; in
recent years, it has been found by means of
the spectroscope to be an exceedingly close
double star. Beta, of the second magnitude,
has also been found to be double by the
same method. Theta, Iota and Epsilon are
of the third magnitude, but do not call for
special mention. Epsilon forms an isosceles
triangle with Eta and Zeta, two stars of the
fourth magnitude very close together. In
Auriga appeared the famous " new star M of
1891.

THE STARS OF WINTER. 49

Perseus. — To the right of Auriga and further
along the stream of the Galaxy, which here
becomes more brilliant, is the well-known
constellation Perseus. This group, one of the
most fascinating in the entire heavens to the
beginner, is very easily identified. Its most
notable feature is a triangle, almost equilateral,
consisting of three stars, Alpha and Beta of
the second magnitude, ■

and Epsilon of the third. #

Almost in the centre of # A

this triangle but nearer • ♦• Y

to Epsilon is a fainter m # • *\ ••

star Nu, of the fourth ^ •*
magnitude. Between **

Alpha and Beta and ^

shghtly above the line •«

joining them is Kappa,
also of the fourth mag-
nitude. ^ .

Alpha Persei is the « k »,

r hiG. 5. — Perseus.

brightest orb in a stream

of stars, which forms the second distinguishing
feature of the constellation. In order, and
beginning from the highest point of the stream,
the stars are Eta, of the fourth magnitude,
Gamma, of the third, Alpha of the second,
Psi of the fifth, Delta of the third. Here the
stream curves sharply round, the stars in the
curve being 48 Persei, Mu and Lambda of the-

(2,015) 4

.50 PEACTICAL ASTEONOMY.

fourth magnitude, and 43 Persei of the fifth.
The only other notable star in the constellation
is Zeta, of the third magnitude, a somewhat
isolated star, considerably below Epsilon.

There are three chief objects of interest in
the constellation Perseus to the ordinary
observer with the unaided eye or binocular.
These are Beta Persei or Algol, the famous
variable ; the region surrounding Alpha Persei,
or Mirfak ; and the double cluster near to the
star Chi Persei.

The name " Algol " is Arabic for " the
demon " ; and from this some astronomers
have assumed that the old Arab astronomers
were acquainted with the variations in its
light. Be this as it may, the fact that the
star is variable was not discovered until com-
paratively modern times, although the varia-
tions are quite easy to follow with the unaided
eye. Probably the reason of this is that the
normal appearance of Algol is that of an ordi-
nary star of the second magnitude. As Mr.
J. E. Gore remarks : " Shining with a steady
light for about 59 hours its lustre suddenly
begins to diminish, and in about 4|- hours its
brilliancy is reduced to about one-third of its
normal brightness. It remains at its faintest
for about 15 minutes, and then in about
5|- hours recovers its former lustre." The
variability of the star was discovered in 1669

THE STARS OF WINTER. 51

by Montanari, an Italian, and again in 1782
by Goodricke, a young English astronomer,
who accurately determined the period, which
is 2 days, 20 hours, 45 minutes, 55 seconds.
Goodricke was the first to suggest that the loss
of light was due to partial eclipse of Algol
by a large satellite, dark, or almost dark.
This theory was confirmed twenty years ago
by the late Professor Vogel of Potsdam, by
means of what is known as Doppler's principle
in spectroscopic observations. Vogel applied
the principle to the observation of Algol, and
he found that before each eclipse Algol was
retreating from the Solar System, while after
each eclipse it showed signs of approach. This
proved conclusively that both Algol and its
invisible companion -star were in revolution
round their common centre of gravity, and
that Algol was not inherently a variable, but
merely a double star. Vogel also ascertained
that in all probability Algol is a star about
one million miles in diameter, and the satellite
star about eight hundred thousand miles —
about equal in size to our sun — the distance
between the centres of the two stars being
about three millions of miles. The presence
of a third member of this remarkable system
has often been suspected, although not yet
confirmed. To the unaided eye Algol appears
only a very ordinary star, with no outstanding

52 PEACTICAL ASTKONOMY.

features ; and it is remarkable that it was an
amateur who discovered its variations, deter-
mined its period, and put forward the true
theory of its variations.

Alpha Persei or Mirfak is the centre of a
remarkable region of the heavens. When we
observe this region with the binocular, we
cannot but be impressed with its magnificence.
There is a festoon of stars round Mirfak,
arranged so symmetrically as to preclude the
idea of a chance scattering.

Above Eta and near to the borders of
Cassiopeia is the star Chi Persei. Near to
this star is the magnificent double cluster
in Perseus. It is visible to the unaided eye
as a hazy spot of misty light. A field-
glass shows it much more plainly ; and even
in a small telescope it is a striking spec-
tacle, while in a large instrument it is awe-
inspiring.

Perseus is notable in astronomical history
as the constellation in which the famous tem-
porary star of 1901 — " the new star of the
new century " — appeared. This star was dis-
covered by the Rev. Dr. Anderson of Edinburgh
in February 1901. At its maximum it sur-
passed Capella in brilliance, and indeed it was
one of the most brilliant temporary stars ever
recorded.

We have briefly surveyed the chief con-

THE STAES OF WINTEK. 53

stellations visible in the winter skies and have
noted their chief stars and the most interesting
binocular fields. Taking Orion as a starting
point, the beginner is enabled to identify the
other groups. After all the others have been
identified, Orion still remains the chief attrac-
tion. As a recent American writer has re-
marked : "I have never beheld the first
indications of the rising of Orion without a
peculiar feeling of awakened expectation like
that of one who sees the curtain rise upon a
drama of absorbing interest. And certainly
the magnificent company of the winter con-
stellations of which Orion is the chief make
their entrance upon the scene in a manner
that may be described as almost dramatic. "
It must not be forgotten that, although the
winter stars may be seen and identified in and
near to cities, they are seen under their most
favourable conditions in the country districts
where the air is clear and pure. As the same
writer has expressed it : "In the pure frosty
air the stars seem splintered and multiplied
indefinitely, and the brighter ones shine with
a splendour of light and colour unknown to
the denizen of the smoky city whose eyes are
dulled and blinded by the blaze of street lights.
There one may detect the delicate shade of
green that links in the imperial blaze of Sirius,
the beautiful rose-red light of Aldebaran, the

54 PRACTICAL ASTRONOMY.

rich orange hue of Betelgeux, the blue- white
radiance of Rigel, and the pearly lustre of
Capella."

CHAPTER IV.

THE STARS OF SPRING.

To the lover of nature the early spring is
always a time of joy and hope ; to the lover
of nature who is also a lover of celestial scenery,
this feeling is tempered by one of regret that
the brilliant constellations of the winter-time
have disappeared from view, for this is the
season described by Tennyson as the time

" When the shining daffodil dies and the charioteer
And starry Gemini hang like glorious crowns
O'er Orion's grave low down in the west."

Leo. — The stars of spring seem very faint in
comparison with their predecessors of winter.
Not only are the stars of spring less brilliant ;
they are also more sparsely scattered. To the
observer who is anxious to become familiar
with the constellations visible at this time
there is one great drawback : there is not
among the spring star-groups a constellation
so brilliant and notable as Orion among those
of winter. There is, however, a group which
is not readily mistaken and whose outline is

THE STARS OF SPRING. 55

easily kept in mind. This is Leo — the
Lion — the fifth of the constellations of the
Zodiac.

Leo may be easily found by means of the
stars of the Plough. A line drawn from
Alpha Ursae Ma j oris — one of the " pointers "
— through Lambda and Mu Ursae Majoris.
directs the observer to the stars of Leo. Per-
haps, however, the constellation may be rec-
ognised without this aid. Even the most

» •.

Fig. 6.— Leo.

casual star-gazer, casting a glance upward on
any evening of spring, can hardly fail to
notice a striking group of stars, east of the
meridian, west of the meridian, or on the
meridian itself, according to the hour of the
night or the earliness or lateness of the sea-
son. The constellation consists of two parts —
on the right-hand side a curve of stars known
as " the sickle " from its resemblance to the
implement of that name, and on the left-hand
side a group of stars in the form of a triangle.

56 PKACTICAL ASTRONOMY.

Between the two parts of the constellation
there is a gap, filled by faint stars.

There are six principal stars in " the sickle " ;
and the star at the bottom at once attracts
attention. It is Regulus or Alpha Leonis,
one of the fainter stars of the first magnitude.
The position of the Sun at the summer solstice
was in this group when the zodiacal constella-
tions were first arranged, and this gave to
Leo and its chief star a primacy not warranted
by the actual importance of constellation or
star. Mr. Maunder has shown this very
clearly in his discussion of Leo in Astronomy
without a Telescope : " Our present name for
the star," he says, " is the variant proposed
by Copernicus, for the older Latin Rex.
Ptolemy calls it ' Basilikus,' the Arabs give
it ' Malikiyy,' ' the kingly ' star, and the
cuneiform inscriptions of the Euphratean
valley refer to it as the ' star of the king,'
whilst in ancient Persia it was the chief of the
four royal stars. It is its place, however, and
not its brilliance which has gained for Regulus
this distinction, for almost all the first magni-
tude stars are its superiors in brilliance."

The next star of the curve is Eta Leonis, of
the third magnitude. Above Eta, next in
the curve, is Gamma, of the second magnitude.
It is a double star visible in the telescope, and
a favourite object for double-star observers.

THE STAKS OF SPKING. 57

The next star in the line is Zeta, of the third
magnitude. At the summit of the curve —
the handle of the sickle — is Mu, of the fourth
magnitude ; while below Mu is Epsilon, of
the third. In a line with Epsilon to the
right-hand side is a fifth magnitude star,
Lambda Leonis.

A little south-west of Zeta is a point in the
heavens, unmarked by any bright star, which
has attracted the attention of astronomers for
many years. There is a famous shower of
meteors or falling stars known as the November
meteors. It was discovered early in the last
century that this shower was an annual one,
generally unnoticed by the casual observer,
but that every thirty-three or thirty-four
years it became a magnificent spectacle. The
paths of the meteors, traced backwards in
the sky, were found to converge at the point
near Zeta Leonis mentioned above. Hence
the meteors were named " the Leonids." The
shower is much less notable now than in former
years, but November never passes without the
appearance of a few meteors radiating from
Leo. It is unnecessary to point out that the
shower is caused by the Earth ploughing ite
way through the shoal of minute bodies known
as meteors, and that the meteors merely ap-
pear to come from a point which lies in the
same line of sight as the constellation Leo.

58 PRACTICAL ASTRONOMY.

Between the Sickle on the right-hand side
of the constellation and the triangle on the
left-hand side there is a dearth of bright stars.
On the left hand of the figure we notice the
three stars, Delta, Theta and Beta, which form
a right-angled triangle, of which Theta marks
the right angle. Beta is of the second magni-
tude and is often spoken of by its Arabic
name " Denebola." Theta is of the third
magnitude and Delta of the second. Beta is
an interesting object in a field-glass, as there
are several fainter stars surrounding it.

Virgo. — Next to Leo, Virgo — the Virgin —
is the most prominent constellation visible
in spring-time. Virgo is the large star-group
to the left-hand side of Leo and lower in the
sky. It is easily identified, its figure resem-
bling a large capital Y lying on its side. The
stem of the Y is marked by two stars, Alpha
Virginis — (Spica) — and Gamma. The latter
star with Eta and Beta forms the right arm
of the figure, and with Delta and Epsilon forms
the left arm. The comparative brightness of
the stars in Virgo and the dearth of other
bright stars near renders the constellation
very conspicuous.

Beginning at the foot of the Y, Spica or
Alpha Virginis is the brightest star of the
constellation. It is of the first magnitude
and of a bluish-white colour. There is nothing

THE STARS OF SPRING. 59

particularly remarkable about the appearance
of Spica to the unaided eye, except its bright-
ness. The remarkable fact concerning it is
that it is a very close double star, so close as
to be invisible in the telescope. By means of
the spectroscope, however, we know that the
bright star has a dark or nearly dark satellite
star. The two stars, which are separated by
only six and a half millions of miles, revolve

• c

r

Fig. 7. — Virgo.

round their common centre of gravity in about
four days, with a velocity of fifty-seven miles
a second ; and the joint mass of the two stars
is two and a half times that of the sun. It is
obvious that in this system we have an arrange-
ment quite different from that in the Solar
System. The equality in size of the two stars
makes it impossible for the one to revolve
round the other. Both revolve round their
common centre of gravity.

60 PEACTICAL ASTRONOMY.

Proceeding up the stem of the Y we reach
Gamma Virginis, of the third magnitude. It
is a famous double star, but of course far
beyond the reach of the binocular. It may
be seen with telescopes of 3 and 4 inches in
aperture. The fainter star requires 185 years
to complete its revolution. Here then we
have a double star of exactly opposite type
from Spica.

The four stars which, along with Gamma,
form the two arms of the Y, are all of the
third magnitude and do not call for particular
attention. It is interesting to note that in
the region of the sky between the arms of the
Y and Beta Leonis, is the point known as the
pole of the Galaxy. That is to say, this
region of the heavens is farthest from the
Milky Way. If we liken the starry sphere to
an immense globe and the Galaxy to the
equator of that globe, this particular region
contains its northern pole. In tnis region of
the sky the stars are most sparsely scattered.

Corvus and Crater. — The sky below Virgo
and Leo is divided between two insignificant
constellations — Corvus, the Crow, and Crater,
the Cup.

Corvus may be recognised by the trapezium
formed by its four chief stars, Delta at the
north-eastern corner, Gamma at the north-
western, Epsilon at the south-western, and

THE STARS OF SPRING. 61

Beta at the south-eastern. Delta, Gamma,
Beta and Epsilon are of about the third mag-
nitude. Near to Delta is Eta, of the fifth
magnitude ; and below Epsilon is Alpha, of
the fourth magnitude. Crater is a less notable
group. The only noticeable stars are Delta
of the third magnitude, Gamma of the fourth,
and Alpha of the fourth. These three stars
form a triangle.

Hydra and Cancer. — On the south and west
of these constellations is the long straggling
group known as Hydra, the longest con-
stellation in the heavens, and one of the most
difficult to identify. Its most brilliant star
is Alpha Hydrae, known by its Arabic name
of "Al Fard"— the "solitary" — the name
possibly being suggested by the barrenness
of the adjacent portions of the sky. Al Fard
is a reddish star of the second magnitude and
from its colour was named by the ancient
Chinese astronomers " the red bird." Al
Fard is really the only notable star in Hydra,
which winds from the borders of Libra to the
borders of Cancer. This notable though faint
constellation may easily be found by means of
the most northern stars of Hydra. These
stars marking the head of the monster are
above Al Fard, on the right-hand side. Di-
rectly above these stars and between Gemini
and Leo, is the little group of Cancer, the Crab.

62 PRACTICAL ASTRONOMY.

Insignificant though Cancer appears, it is the
fourth of the zodiacal constellations. The
stars Gamma, Delta, Zeta and Mu form a
quadrilateral ; while Delta and Mu, the two
lowest stars of the quadrilateral, form a trape-
zium with Alpha and Beta. The most notable
feature in the constellation is, however, the
cluster " Praesepe," or the " Bee-Hive." This
is visible to the unaided eye as a hazy cloud-
like object between the two fourth-magnitude
stars Gamma and Delta Cancri. Next to the
Pleiades, this is the most conspicuous star-
cluster in the heavens. It was noted by the
ancient astronomers, who, however, failed to
detect the individual stars and classified it as
a " nebula " or little cloud — this being the first
occasion on which this term was applied to a
celestial object. Praesepe is a striking object
in a binocular and in a small telescope, although
much less noticeable than the Pleiades.

Two other insignificant groups may be noted
among the spring constellations. Above Virgo
and on the left-hand side of Leo is the constella-
tion of Coma Berenices, which although not one
of the original constellations — named in pre-
historic times — is yet very ancient. The name
signifies the " hair of Berenice," Queen of
Egypt. This princess — the story goes — vowed
her hair to the gods if her husband returned
safely from a war in which he was engaged.

THE STAES OF SPKING. 63

Her hair was stolen from the temple in which
it had been placed after her husband's return,
whereupon the royal astronomer of the day
declared it had been translated to the celestial
regions, and pointed to the shimmering star-
group as proof of the truth of his assertion.
The constellation, while destitute of bright
stars, possesses a number of faint ones and is
an interesting field for the binocular.

Above Leo and Virgo and below the Plough
is another insignificant constellation, Canes
Venatici, the " Hunting Dogs." This con-
stellation, indeed, is almost circumpolar, but
is at its best position for observation in
spring. There is only one bright star, desig-
nated Alpha, which is easily found when the
Plough is known ; for it is the next bright star
to Eta Ursae Majoris, the last star of the handle
of the Plough. It is also known by the some-
what ludicrous name of Cor Caroli, " Charles's
Heart." It was so named because it was
believed by the Royalists to have shone with
exceptional brilliance on the evening before
Charles II. made his entry into London for
the first time after the Restoration. There
are no other bright stars in the constellation.
To the telescopic astronomer it is chiefly fa-
mous on account of the famous spiral nebula.
This magnificent object, however, is far beyond
the reach of the unaided eye or binocular.

64 PEACTICAL ASTRONOMY.

The constellations Bootes and Corona Bore-
alis are by some astronomers included among
the stars of spring ; but it is more correct to
include them among the summer stars. They
are certainly visible in spring-time, but they
are most prominent of all in the short summer
nights. Therefore in this work they will be
described among the summer stars — in the
next chapter.

The average observer of the heavens cannot
fail to be impressed with the scarcity of bright
stars in spring-time. In the winter skies,
described in the last chapter, no less than
seven stars of the first magnitude are visible —
Sirius, Betelgeux, Rigel, Procyon, Aldebaran,
Capella and Pollux, along with a large number
of bright stars of the second magnitude. On
the other hand, Regulus and Spica are the
only first-magnitude stars among the spring
constellations proper. Not only are there
few bright stars in spring, but as compared
with other seasons of the year there is a
remarkable dearth of stars of all magnitudes.
The reason of this is not far to seek, and al-
though its consideration leads into the higher
problems of astronomy, it may be mentioned
here.

As was seen in a previous chapter, the Milky
Way or Galaxy is the ground-plan of the
Universe. It is itself an agglomeration of

THE STARS OF SPRING. 65

many millions of stars, individually invisible
to the unaided eye, which are seen collectively
as a belt of misty light. t Not only is the
Galaxy an agglomeration of faint stars, but it
is a region of the heavens in which the bright
stars are most thickly scattered. The late
Mr. Gore, one of the ablest of non-professional
astronomers, examined the positions of all
the bright stars on the northern hemisphere.
He found that, of thirty-two stars brighter
than the second magnitude twelve lie on the
Milky Way or on faint nebulous light con-
nected with it ; and of those brighter than
the third magnitude thirty-three stars out of
ninety-nine lie on the Galaxy. Thus, the
number of brighter stars is considerably more
than that due to the area of the Galaxy. In
summer, autumn, and winter, we see the
Milky Way more favourably than in spring.
At this season of the year the part of the
heavens exposed chiefly to our view is the
region near to and round about the pole of the
Galaxy. The stars increase in density from
the pole of the Galaxy to the Galaxy itself ;
therefore the region round about Leo, Virgo,
and Hydra is naturally the least rich region
of the heavens.

This is the explanation of the relative
paucity of stars in the skies of spring. In
summer, although owing to the length of day-

(2,015) 5

66 PEACTICAL ASTRONOMY.

light we see less of the starry heavens than in
spring, richer and more crowded regions come
into view. These will be considered in the
next chapter.

CHAPTER V.

THE STARS OF SUMMER.

" In the soft air of a summer night," says
an American astronomer, "when fireflies are
flashing their lanterns over the fields, the stars
do not sparkle and blaze like those that pierce
the frosty skies of winter. The light of Sirius,
Aldebaran, Rigel and other midwinter bril-
liants, possesses a certain gem-like hardness
and cutting quality, but Antares and Vega,
the great summer stars, and Arcturus, when
he hangs westering in a July night, exhibit a
milder radiance, harmonising with the char-
acter of the season." This description is true
to nature : the light of the summer stars is
different from those of winter, but the differ-
ence is chiefly atmospheric ; there is no pecu-
liar quality in the light of the various stars
which are visible in summer-time.

The chief drawback to the study of the
constellations in summer is the fact that the
period of actual darkness is so brief. The
summer stars, in short, are not so obvious as

THE STARS OF SUMMER. 67

those of winter. They do not intrude them-
selves on the view of the observer ; it is neces-
sary for him to look for them. They are none
the less interesting on this account ; there is
indeed a certain charm in watching the summer
sky darkening as midnight approaches and the
shy stars peeping out one by one in the heavens.

But the student of the

•p

summer skies must be en-
thusiastic. His interest in •
the heavens must be first %b
stimulated by observation
of the constellations which
dominate the skies of ^€
winter and spring respec-
tively.

Bootes. — The chief con-
stellation of the summer . ®
skies is identified by its * 7
principal star, Arcturus. •
This star is very easily ^JB.8^BooleB.
recognised. A line drawn
from Eta Ursae Ma j oris, the last star in the
handle of the Plough, will reach Arcturus.
This is one method of finding the star ; but
Arcturus is so obvious that it will attract
the attention of the most casual observer.
But for the presence of this brilliant star the
constellation Bootes would be in no way re-
markable. At the top of the constellation

68 PRACTICAL ASTRONOMY.

is a triangle formed by three stars — Beta,
Gamma and Delta. Delta, at the left-hand
corner of the triangle, is almost in a straight
line with Epsilon Bootis and Arcturus ; while
Arcturus itself forms a triangle with other two
fainter stars Eta and Zeta. The figure of
Bootes is one not easily remembered, and al-
though the method of remembering the stars
by means of lines and triangles has, speaking
generally, many drawbacks, in the case of
Bootes it is the only method practicable.

Arcturus, or Alpha Bootis, is one of the most
brilliant stars in the heavens. The majority
of astronomers consider Arcturus to be slightly
more brilliant than Vega and Capella ; but
there is not unanimity on this point, for the
three stars are of different colours, Vega being
bluish-white, Capella bright yellow, and Arc-
turus a deeper yellow, shading into orange.
It is therefore difficult to determine the minute
differences in magnitude ; yet the majority
of astronomers believe Arcturus to be the
brightest of the three. It is therefore the
most brilliant star north of the celestial equator,
and with the exception of Sirius, the brightest
star visible to observers in the northern hemi-
sphere.

Arcturus, which is situated at an enormous
distance from the Solar System, appears to be
a star of gigantic size. Dr. Elkin, an American

THE STARS OF SUMMER. 69

astronomer, made an attempt to measure the
distance of Arcturus. He found that the
star's displacement, due to the change in the
observer's position, when he is at exactly op-
posite points of the Earth's orbit — in January
and July respectively, for instance — is about
equal to the apparent distance between the
heads of two pins placed an inch apart and
viewed from a distance of about 180 miles.
The distance deduced from Dr. Elkin's meas-
urement is of course by no means beyond
doubt ; but assuming that the estimate is
fairly near the truth, Mr. Garret P. Serviss,
an American astronomer, has calculated that
if the Earth were situated midway between the
Sun and Arcturus it would receive over 5000
times as much light from the star as from the
Sun ; and assuming that the radiation of the
star is the same per unit of surface as the Sun,
he finds that Arcturus exceeds the Sun in
volume by about 375,000 times.

Of the other bright stars in the constellation,
Epsilon is of the second magnitude, Eta, Zeta,
Gamma and Delta of the third, and Beta and
Mu of the fourth.

Mr. Maunder compares Bootes to Orion,
remarking that when Arcturus is excluded,
" the principal remaining stars of the con-
stellation make up a representation, pale and
distorted, it is true, but a representation for all

70 PKACTICAL ASTRONOMY.

that of the most glorious constellation in the
sky." This idea may assist the observer in
tracing the shape of Bootes.

Corona Borealis. — To the left of Bootes is
a constellation which although small is very
conspicuous — Corona Borealis, or the Northern
Crown. The group is shaped exactly like a
coronet, and, as it really resembles the object
after which it is named, it is easily identified
and as easily remembered. There are six
chief stars in the constellation. Beginning at
the right-hand side, the stars are in order —
Theta, Beta, Alpha, Gamma, Delta and Ep-
silon. Alpha is of the second magnitude and
the others of the fourth.

In this constellation, in 1866, appeared the
famous temporary star known as " the blaze
star." It was discovered by an Irish amateur
astronomer who, on casting a glance round
the skies, saw the familiar configuration of
Corona Borealis completely altered by the
presence of a brilliant stranger. Four hours
earlier it was not visible ; in a few hours
some mighty conflagration had taken place,
which caused the star to shine with at least
nine times its former brilliancy ; for it is
believed that it was known as a minute tele-
scopic object before the outburst.

East of Bootes and Corona Borealis is a
region of the heavens which is probably one

THE STAKS OF SUMMER. 71

of the most difficult for the observer to know
thoroughly. As our glance travels eastward
along the heavens we reach richer regions
where the stars are more profusely scattered ;
for we are again approaching the vicinity of
the Milky Way, one of the branches of which
passes through Ophiuchus and Serpens. The
stars are not grouped in easily remembered
figures, nor are the constellations themselves
marked off one from the other. Serpens and
Ophiuchus, for instance, intersect in a manner
which is very puzzling to the beginner in
constellation study. The key to this inter-
section is found in the names of the star-groups
themselves. " Serpens " is Latin for " the
Serpent " while " Ophiuchus " is " the Serpent-
bearer." On the old globes in which the
mythical figures are represented, Ophiuchus
the serpent-bearer is represented as engaged
in a life-and-death struggle with the serpent
which is coiled round him. The natural
grouping of the stars has in this case been ig-
nored for the purpose of representing the old
fable in the sky, with the result that it is
very difficult for the beginner to recognise
which stars belong to Serpens and which to
Ophiuchus. Above these two groups is
Hercules, which, although not a striking con-
stellation, is much easier to follow.

Hercules. — On the left of Corona Borealis

72 PRACTICAL ASTRONOMY.

and somewhat higher in the sky than that
constellation, our attention is attracted by
four stars which form a quadrilateral which is
almost a square. These four stars are Pi of
Hercules, on the top left-hand corner, Eta on
the top right-hand corner, Zeta on the bottom
right-hand, and Epsilon on the bottom left-
hand. All four are of the third magnitude.
Close to Pi is Rho, of the fourth magnitude,
while on a straight line from Eta to Zeta, but
considerably nearer to the former star, is the
famous star-cluster in Hercules. This wonder-
ful celestial spectacle is beyond the reach of
the unaided eye, but it may be noticed if looked
for with the binocular and seen fairly well
with a small telescope. Larger instruments
have shown it to be one of the most wonderful
objects in the entire heavens — containing many
thousands of stars. For many years it was
believed that the cluster represented a mere
local aggregation of stars, but our whole con-
ception of its place in the Universe has been
revolutionised by a remarkable investigation
carried through within the last few years by
a distinguished American astronomer, Dr.
Harlow Shapley. From an exhaustive study
of the colours and absolute maguitudes of the
stars in the cluster Dr. Shapley reached the
conclusion that it is situated at a distance so
great that light requires 100,000 years to

THE STARS OF SUMMER. 73

travel from the cluster to our system, and
1100 years to cross from one side of the cluster
to the other. In fact, the cluster is possibly
an " island universe," though considerably
smaller in extent and perhaps not altogether
independent of our Galaxy. That it is analo-
gous in its nature is shown by the recent work
of Dr. Sbapley, who has detected the presence of
a zone of galactic concentration in the cluster,
similiar to the Milky Way. Professor Edding-
ton has truly remarked that " were we trans-
planted into the midst of the great Hercules
cluster our knowledge of its constitution could
scarcely be so precise as that which Mr. Shapley
has discovered at a distance of 100,000 light
years ; and the labour would have been in-
comparably greater."

Thus when we observe the cluster it is well to
realise that we are looking far beyond the limits
of the Stellar System into vistas of infinity.

From the quadrilateral in Hercules the other
stars of the constellation may be found. Al-
most directly below Zeta is Beta, of the
second magnitude, the space between Zeta
and Beta being a little greater than that
between Zeta and Eta. Close to Beta, but
slightly lower in the sky, is Gamma, between
the third and the fourth magnitude. To the
left of the quadrilateral is a portion of the
heavens in which it seems at first very difficult

74 PRACTICAL ASTRONOMY.

to discern any order in the scattered stars.
There is, however, a curve of stars which may
be remembered. Beginning with Beta after
a considerable space we come to Delta, of the
third magnitude. As far from Lambda as
Lambda is from Delta, we come to Mu, of the
third magnitude. The curve turns more sharply,
and we reach Xi and Nu, two fourth-magnitude
stars comparatively close together. Again
there is a considerable gap and we reach Theta,
also of the fourth magnitude, which is almost
in a straight line with three stars — so that the
curve becomes practically straight. These are
a fifth-magnitude star marked 90 Herculis, Iota
of the third magnitude, and Beta Draconis of
equal brightness. In fact Iota Herculis is
naturally one of the four stars forming the
notable diamond-shaped figure in Draco — the
other three being Xi, Beta and Gamma Dra-
conis.

Ophiuchus and Serpens. — Alpha Herculis, a
bright reddish star, irregularly variable, may
be found almost directly below Delta — a con-
siderable stretch of sky intervening. Close to
this star is Alpha Ophiuchi. So close indeed
are the two stars that Alpha Herculis seems to
belong more naturally to Ophiuchus than to
Hercules. Below Alpha Ophiuchi, a second-
magnitude star, is Beta of the third magnitude ;
and again below this star, although not in a

THE STAES OF SUMMER 75

straight line but in a line slanting to the left,
is Gamma, of the third magnitude. We may
note that in this constellation appeared the
famous new star of 1604. In this same group,
too, is situated a faint star with a very large
" proper motion," discovered by Professor
Barnard of the Yerkes Observatory in 1916.
This faint star is situated at a distance which
light requires a little over six years to traverse.
It is with the single exception of Alpha Cen-
tauri our nearest known stellar neighbour.
Obviously, it must be one of the smallest and
faintest of the stars.

We may now direct our attention to Serpens,
which begins below Corona Borealis in the
space between Hercules and Bootes. A wind-
ing stream of stars may be traced from near
the boundaries of Hercules — Kappa Serpentis
of the fourth magnitude, Beta of the third,
Delta of the third, Alpha of the second (near
to which is Lambda of the fourth), Epsilon
of the third, and — after a considerable gap —
Delta, Epsilon and Zeta of Ophiuchus. It is
almost impossible to remember these stars
from any figure or grouping. They must be
followed star by star, and it is fortunate for
the observer that they generally run in lines
and streams. There are some magnificent
binocular fields in Serpens, which is well worthy
of careful attention.

76 PEACTICAL ASTKONOMY.

Lower down in the heavens are the three
least-known constellations visible to north-
ern observers — Libra, Scorpio and Sagittarius.
These, which are zodiacal constellations, only
rise a short distance above the horizon ; and
as their period of visibility is in summer-time,
when the evenings are so long clear and the
period of darkness is brief, these star-groups
are among the least known in the heavens.

Libra. — Libra, or the Scales, the seventh
constellation of the Zodiac, lies east of Virgo
and considerably lower in the heavens. Alpha,
Delta and Beta form a triangle. Alpha is
almost exactly on the ecliptic, the line which
marks the Sun's apparent path in the heavens.
In the field-glass this star is a beautiful double.
Beta is of a greenish hue. This star is believed
to have decreased in magnitude within the
last two thousand years. It is now of the
second magnitude ; whereas Ptolemy cata-
logued it as a star of the first magnitude.

Scorpio. — Next to Libra, but more conspic-
uous although lower in the sky, is Scorpio
— the Scorpion — the eighth constellation of the
Zodiac, or rather the part of Scorpio which is
visible to observers in our northern latitudes.
In more southern latitudes Scorpio is one of
the most magnificient constellations in the
heavens ; it is not only rich in stars but it is
immersed in one of the most brilliant portions

THE STARS OF SUMMER. 77

of the Milky Way. The star Xi of Scorpio,
which is on a line with Mu Serpentis, is the
first of the curve of stars which distinguish the
northern portion of the star-group. Below Xi
lies Nu, and from Nu the curve includes Beta,
Delta, Sigma, Alpha and Tau. Alpha, better
known by its Greek name of Antares, is a star

Fig. 9. — Scorpio.

of the first magnitude. It is of a fiery red
colour, hence its name of " Ant- Ares," the rival
of Ares or Mars. It is a star of the same
spectral type as Betelgeux in Orion. When
observed with a good telescope it is seen to be
a double star, the little satellite-orb being of a
greenish colour. For many years these colours
— red and green — were thought to be the effect

78 PKACTICAL ASTRONOMY.

of contrast, but the spectroscope has shown
that the colours are real.

The constellation is full of interesting and
beautiful fields even for an opera-glass ; and if
Scorpio were seen in winter, spring or autumn,
it would probably be one of the most familiar
and most thoroughly explored of star-groups ;
but its slight elevation above the horizon and the
fact that it is only seen in the summer months
render it less interesting to the beginner than
its brilliance and importance warrants.

Sagittarius. — The ninth constellation of the
Zodiac, Sagittarius the Archer, lies to the
left-hand side of Scorpio, but slightly higher
in the heavens. Although more elevated,
however, it is less brilliant than Scorpio and
possibly less familiar ; while it is certainly less
easy to follow. It is chiefly notable for the
presence of the Milky Way, which is here very
brilliant ; and in the evenings of late summer,
this part of the Galaxy, low down in the south-
west, shines with a strange brilliance. The
chief stars of Sagittarius visible to northern
observers — included in a curve which begins
near the borders of Ophiuchus — are Mu,
Lambda, Delta and Epsilon, the three latter
being set in the stream of the Milky Way.
In the southern parts of Sagittarius the Milky
Way divides into two branches, one branch
running into Scorpio and Ophiuchus and the

THE STARS OF SUMMER. 79

other running straight through Sagittarius into
Aquila.

Lyra. — This star-group cannot be mistaken.
It lies to the left of Hercules and to the right
of the stream of the Galaxy. Its most dis-
tinguishing feature is its brightest star, Vega
or Alpha Lyrae. In the chapter on the
northern stars, reference has been made to
Vega, which like Capella is a circumpolar star,
and which occupies the position in summer
which Capella holds in winter, being high in
the sky. Vega, whose light is of a bluish-white
tinge, is one of the most brilliant stars in the
sky. It appears to be situated at an immense
distance from the Solar System, and to be a
star of about three or four times the light-
giving power of Sirius, which considerably out-
shines our Sun.

The configuration of Lyra is easily remem-
bered. On the left of Vega are three stars
of the fourth magnitude, Epsilon, Zeta and
Delta, and two of these, Epsilon and Zeta,
form with Vega an equilateral triangle. Be-
low Vega are Beta and Gamma Lyrae, both
of the third magnitude, which form a quadri-
lateral with Delta and Zeta. These are the
chief stars of the constellation.

Of these stars Beta is notable as a famous
variable star, the variations of which are easily
within reach of the unaided eye. It varies

80 PRACTICAL ASTRONOMY.

from the third to the fourth magnitude in 12
days 21 hours 47 minutes. The variations of
this star are believed to be due to the revolu-
tion of two stars, one less brilliant than the
other round their common centre of gravity.
The stars, according to Newcomb, are of
unequal size and almost in contact, and the
smaller body is much brighter than the larger.
The system thus revealed is certainly one of
the most remarkable in the heavens. This
variable star is a very suitable object for the
observer who is commencing the study of
variables, as its changes can all be followed
by the unaided eye.

Epsilon Lyrae is a double star, visible as
such to keen eyesight. The binocular easily
reveals the star as double, and a small tele-
scope shows each of the two to be itself double ;
so in Epsilon Lyrae we have a quadruple star.
Perhaps, however, the most interesting star in
the constellation is Delta Lyrae, not on account
of the star itself, but on account of a point in
the sky near it. The most reliable astronom-
ical calculations have shown that the Sun,
carrying with it the Earth and the planets, is
travelling towards this portion of the heavens
with a velocity of about eleven miles per
second. As Sir Robert Ball has remarked :
" The speed with which this motion of our
system is urged is such as to bring us every

THE STARS OF SUMMER. 81

day about 700,000 miles nearer to this part
of the sky. As you look at Delta Lyrae
to-night, you may reflect that within the last
twenty-four hours you have travelled towards
it through a distance of nearly three-quarters
of a million of miles. So great are the stellar
distances that a period of not less than 180,000
years would be required before our system, even
moving at this impetuous speed, could traverse
a distance equal to that by which we are
separated from the nearest of the stars." The
observer may be tempted to ask, when then
shall we reach Delta Lyrae ? In all proba-
bility we shall never reach it. For the star,
like our own Sun, probably has its own motion,
and even when our system in the course of
thousands of thousands of years — if it is then
in existence — does reach the place now occupied
by Delta Lyrae, that star will be far away
from its present position. As we contemplate
the region of the heavens towards which we
are moving, surrounding this little star, great
thoughts of our world and its destiny arise in
our minds.

Some astronomers regard Cygnus and Aquila,
the adjacent star-groups, as summer con-
stellations ; but we shall consider them as
autumn groups, because, although well seen
in summer, they are seen in their full glory in
the autumn season.

(2,015) 6

82 PRACTICAL ASTRONOMY.

CHAPTER VI.

THE STARS OF AUTUMN.

In the calm clear skies of autumn the most
notable feature on a moonless night is the
majestic sweep of the Galaxy spanning the
heavens like a great arch. In September and
October the Milky Way is seen to its fullest
advantage ; and in its course in this part of
the heavens it passes through some of the
most wonderful regions of the sky. At this
season of the year it is easier to comprehend
the true nature of the Milky Way than at
others. As was mentioned previously, it is the
ground-plan or equator of the entire Universe
of stars ; the stars are there much more nu-
merous than in other portions of the heavens.
A number of observations with a telescope or
even with a binocular is sufficient to show
that this crowding of the stars towards the
Galaxy is a fact. In a telescopic or binocular
field, in this very region the observer may
count as many as fifty or sixty stars ; while
in an equal field in Virgo or on any part of the
heavens, near to the galactic poles, he may
count as few as five or six. The Galaxy is the
fundamental reference plane of the entire Uni-
verse, just as the equator is of the Earth. In

THE STARS OF AUTUMN. 83

this chapter we shall discuss the constellations
of autumn, beginning with those on the
Galaxy.

Cygnus. — Looking up to the heavens on
an autumn evening, and glancing along the
Galaxy, it is impossible to overlook what is,
if not the most brilliant, perhaps the most
interesting constellation in the entire heavens.
Cygnus, the Swan, is immersed in one of the
most brilliant parts of the Milky Way. It is
situated to the left of Lyra, but it is so con-
spicuous that no directions are required to find
it. The constellation is shaped like a cross ;
indeed so obvious is the cruciform shape that
it has often been termed the " Northern
Cross." At the centre of the cross is the star
Gamma. The horizontal arm of the cross is
marked by Epsilon, Gamma and Delta, be-
ginning at the left-hand side. The perpendicu-
lar arm is marked by Alpha, Gamma, Eta and
Beta, beginning with the uppermost star,
almost in a straight line. In addition there
is another bright star, Zeta, not included in
the cruciform figure.

Of all constellations Cygnus includes the
greatest variety of notable stars from the point
of view of the observer with the unaided eye or
binocular. Beginning with Gamma, the cen-
tral star of the constellation, of the second
magnitude, it is to be noted that it is the

84 PRACTICAL ASTRONOMY.

central star of a very wonderful region, being
itself the last star of a curve or crown of
stars. Alpha Cygni, also known by its Arabic
name of Deneb, is one of the faintest stars of
the first magnitude ; and the region surround-
ing this star is even more striking than that
round Gamma Cygni. The star is thickly
immersed in the Galaxy and well repays ob-
servation with the binocular. The boundary

• < #!

Fig. 10. — Cygnus.

between the galactic light and the darkness of
the small rift in the Milky Way near the star
is marked by a stream or line of stars which
appears distinctly connected with the nebulous
light of the Milky Way.

With the aid of the binocular it is easy
to find 61 Cygni, the second nearest star in the
northern hemisphere. In a straight line from
Alpha Cygni, parallel to the horizontal arm of
the cross, we reach Nu, a star of the fourth

THE STARS OF AUTUMN. 85

magnitude. Prolonging the line not quite so
far as the distance from Alpha to Nu, we
reach a faint star of the fifth magnitude. This
is the famous 61 Cygni, one of the nearest stars
in the heavens. This star is distant from the
Solar System 459,000 times the distance of the
Earth from the Sun. Light requires about
seven^years to reach the Earth from this star,
which is thus much nearer to the Solar System
than any of the most brilliant stars in the
northern sky. Relatively to the Sun, it is a
very small star.

To the naked-eye observer, the brilliance
of the Galaxy in Cygnus is very noticeable.
There is a luminous spot north of Alpha, and
between Beta and Gamma the galactic light
is very brilliant. Perhaps, however, the most
remarkable object in the constellation is the
star Beta, of the third magnitude. A field-
glass, or better still a small telescope, shows
the star to be double, the large star, of the
third magnitude, being topaz yellow and the
smaller one sapphire blue. A view of this
star is a never-to-be-forgotten spectacle.

At the risk of a digression we may turn
our attention briefly to the coloured stars,
such as Beta Cygni, and to the conditions exist-
ing on planets revolving round any of these
stars. Proctor, in one of his books, discussed
the scene visible from any planets situated

86 PEACTICAL ASTRONOMY.

thus. He supposed one of the stars to be blue
and the other orange — as is practically the
case with Beta Cygni — and the planet to be
placed in the same position as the Earth in
our system. There would be an endless variety
of sights in the heavens. The blue and orange
suns might rise together and produce " double
day," or the blue sun might rise as the orange
sun was setting and there would be no night.
The clouds would present extraordinary ap-
pearances, some parts shining blue, some parts
orange, according to whichever sun happened
to shine direct upon them. The case is of
course hypothetical. It must be borne in
mind that such systems must be completely
different from the solar family. In our system
we have one bright star holding sway over a
number of planets. In these systems there
are two suns, which may or may not have
planets revolving round them. If such planets
do exist, and there is no reason why they
should not, they will certainly experience very
varied sights in their skies.

Aquila. — Proceeding downwards along the
stream of the Galaxy we come to the constella-
tion Aquila, the Eagle. This constellation is
easily recognised by its three chief stars Gamma,
Alpha and Beta, close together and almost in a
straight line. The same line prolonged down-
wards reaches Theta. In a straight line

THE STAKS OF AUTUMN. 87

with Theta, pointing north-west, are other
two stars, Eta and Delta. At the extreme
north-western corner of the constellation are
two stars Zeta and Epsilon ; and at the south-
western extremity is Lambda.

Of the stars in Aquila, Alpha is of the first
magnitude, Gamma, Theta, Delta and Zeta of
the third ; Beta between the third and the
fourth, and Epsilon and Lambda of the fourth.
Eta is a variable star, varying from the third
magnitude to the fourth in 7 days 4 hours.

Alpha Aquilae, better known by its Arabic
name of Altair, stands midway between Beta
and Gamma. It is a bright star of the first
magnitude, of a bluish- white tint. It has been
calculated that light requires about seventeen
years to travel from Altair, and whether this
calculation be correct or not, it is certainly
nearer than many other stars of the first magni-
tude. The Galaxy is very bright in Aquila,
although scarcely so striking as in Cygnus.
Lambda stands on a bright spot of milky
light, which is known as Scutum Sobieskii —
" Sobieski's Shield."

On June 8, 1918, a brilliant temporary star
blazed out in Aquila, close to the boundary
of Serpens. At maximum it surpassed Nova
Persei, and was the most brilliant "Nova"
since 1604. By September its light had de-
creased to the fifth magnitude. As in the case

88 PRACTICAL ASTRONOMY.

of Nova Persei, Nova Aquilae was observed
independently by a number of observers.

Between Aquila and Cygnus are three in-
significant little groups which scarcely deserve
to be designated as constellations. Above the
three stars, Gamma, Alpha and Beta is Sagitta,
the Arrow, which contains no very remarkable
objects and might well be included in Cygnus
or Aquila. To the left and slightly lower in
the heavens is Delphinus, the Dolphin, the
most conspicuous of the three groups. It lies
to the left of the Galaxy and is easily noted on
a clear night. There are four stars arranged
in the form of a trapezium, Alpha and Beta
on the right, Gamma and Delta on the left.
Beta is of the third magnitude and the other
three of the fourth. Above Delphinus is Vul-
pecula, the Fox. It contains no notable stars,
and is generally disregarded by astronomers.

Capricornus. — Below Aquila and to the left
of Sagittarius is Capricornus, the Goat, the
tenth of the zodiacal constellations. The chief
stars of Capricornus, Alpha and Beta, may
be easily found exactly below Altair, much
lower down in the heavens. The sky is much
more barren here than in Aquila, for the Galaxy
slopes away into Sagittarius and Scorpio.

Alpha Capricorni, the uppermost of the two
stars, is a double star, visible to the unaided
eye, and well seen in a binocular. The two

THE STARS OF AUTUMN. 89

stars have no connection, and merely appear
close together because they are in the same
line of vision. Beta is also a double star, as
seen in the binocular. Both Alpha and Beta
are stars of the third magnitude. Almost in
a line with Beta are the stars Theta, Iota and
Gamma of the fourth magnitude, and Delta
of the third. They are not, however, in any
way notable. On the whole Capricornus is not
a particularly interesting constellation to the
observer either with the unaided eye or the
binocular.

Aquarius and Pisces. — A similar remark ap-
plies to Aquarius and Pisces, the eleventh
and twelfth constellations of the Zodiac
respectively. Aquarius fills a large part of
the heavens, stretching from the boundaries of
Aquila above Capricornus down to the horizon.
Alpha Capricorni is almost in a straight line
with Epsilon, Mu, Beta and Alpha Aquarii.
Epsilon is of the fourth magnitude, Mu of the
fifth, and Beta and Alpha of the third. Close
to Alpha is a compact group of four stars, the
most notable feature in the constellation —
Gamma, Zeta, and Eta almost, but not quite,
in a straight line, and Pi above Zeta. Gamma
and Zeta are of the third magnitude, Eta of
the fourth and Pi of the fifth. Below this
group is a quadrilateral, consisting of Lambda,
Theta, Iota, and Delta. On a clear autumn

90 PKACTICAL ASTKONOMY.

evening a bright star is sometimes to be seen
glimmering below Aquarius. This is Fomal-
haut, of the first magnitude, the chief luminary
of the southern constellation Pisces Austrcdis,
the Southern Fish. This star is only seen on
evenings when the horizon is specially clear.

Pisces — the Fishes — the twelfth constella-
tion of the Zodiac, is, like Aquarius, an unin-
teresting constellation with no bright stars, but
it is easy to follow, owing to the symmetrical
arrangement of its stars. The chief stars be-
ginning at the borders of Aquarius are Beta,
Gamma, Iota, Omega, 41 Piscium, Epsilon,
Mu, Nu, Xi, and Alpha. Another stream runs
upwards from Alpha, and includes Pi, Eta,
Rho, Chi, and Upsilon, Eta, and Gamma, the
brightest stars of the constellation, are of the
fourth magnitude.

Cetus. — To the left of Aquarius and lower
down in the heavens than Pisces is the large
constellation Cetus, the Whale. The figure of
Cetus is fairly easy to follow. Mr. Maunder
compares it to that of a lounge chair. Alpha,
Gamma, Delta, and Omicron mark the head-
rest of the chair. Zeta and Tau, Theta, Eta,
and Beta form the lower portion of the figure.
Alpha and Beta are of the second magnitude,
Gamma, Zeta, Tau, Theta, and Eta of the
third, and Delta of the fourth. The most re-
markable star in the constellation is Omicron,

THE STAES OF AUTUMN. 91

generally known as " Mira Ceti " — the won-
derful star of Cetus. It is one of the most re-
markable of variable stars. Unlike Algol and
the other variables which have been noted in
previous chapters, Mira runs through its cycle
of variations not in days, but in months. The
period is not regular, like the short-period vari-
able stars, but varies considerably. On the
average it is about 331 days. The star has
been under observation for three centuries, and
has been followed through many cycles. It
varies from the third to the ninth magnitude
as a rule, but sometimes at maximum it is
much more brilliant, and has been known to
reach the first magnitude. The variations of
Mira have never received any completely satis-
factory explanation ; they are certainly not
due to eclipse, like Algol and Beta Lyrae.
Probably they result from great internal
disturbances.

Eridanus and Aries. — Between Cetus and
Orion is Eridanus, the River, described in the
chapter on the winter constellations. Above
Cetus and to the left of Pisces and the right
of Taurus is Aries, the Ram, the first of the
zodiacal constellations. There are only three
bright stars, Alpha, Beta, and Gamma, arranged
in a neat little group, Beta and Gamma being
close together. Alpha is of the second magni-
tude, Beta of the third, and Gamma of the

92 PKACTICAL ASTRONOMY.

fourth. Gamma is a double star, the first
discovered telescopically, in 1667 ; but it is
beyond the reach of the binocular.

Pegasus. — Returning to Aquarius we recog-
nise above that star-group a very noticeable
constellation in a somewhat barren part of the
sky — Pegasus, or the Winged Horse. The
most notable feature about Pegasus is the so-
called " Great Square of Pegasus," although
strictly speaking the title is incorrect, for the

Fig. 11. — Pegasus.

star at the top left-hand corner belongs to the
neighbouring constellation Andromeda. It is
impossible to fail to recognise Pegasus. The
great square is one of the most notable con-
figurations in the heavens, not only on account
of the brightness of the stars forming it, but
also because of the dearth of bright stars
within the figure itself. All four stars of the
square are of the second magnitude. Beta
Pegasi is at the top right-hand corner, Alpha

THE STARS OF AUTUMN. 93

at the bottom right-hand corner, and Gamma
at the bottom left-hand corner.

Close to Beta are Mu, and Lambda, of the
fourth magnitude. An irregular quadrilateral
is formed by Alpha, Zeta, Theta, and Epsilon,
all of which are easily identified.

Andromeda. — Although Pegasus is so notice-
able a constellation, it is singularly barren
in interesting stars or binocular fields. Of
more interest is the neighbouring constella-
tion Andromeda. As already mentioned, Alpha
Andromedae is the star at the top left-hand
corner of the great square.

Almost but not quite in a straight line with
Alpha are Beta and Gamma Andromedae ;
all three are of the second magnitude. Be-
tween Alpha and Beta, but below the imaginary
line joining them, are Delta of the third mag-
nitude, and Epsilon of the fourth. Delta of
the third and Epsilon of the fourth are almost
in a straight line with Pi ; perpendicular to
the line joining Alpha, Beta, and Gamma, is
a line which almost joins Mu, Nu, and Beta.
The star Nu is only interesting on account of
its proximity to one of the most famous objects
in the heavens — the great nebula in Androm-
eda. This famous nebula is easily visible to a
person of average eyesight, being faintly visible
to the unaided eye. It is well seen in a binoc-
ular, and even in a small telescope it is a very

94 PRACTICAL ASTRONOMY.

impressive spectacle. This nebula rivals the
great nebula in Orion as a celestial spectacle ;
it has been closely studied by astronomers for
many years, and since the application of
photography to the heavens its study has
proceeded with greater rapidity than ever.
Formerly it was believed that the nebula was
a cluster of stars, too distant for the individual
stars to be separately visible. Later, the
general view was that it was a true nebula, a
mass of gas in a more condensed state than
that in Orion. Recently, however, photo-
graphic and spectroscopic research seems to
indicate that it lies beyond the Stellar System
and may possibly be an external galaxy, too
far away for the individual stars to be sepa-
rately visible. But in this case there is not the
same degree of certainty as in that of the
cluster in Hercules.

In 1885 a temporary star appeared in the
centre of the nebula. Other three have been
detected in recent years.

Between Andromeda and Aries is the little
constellation of Triangulum, the Triangle.
The constellation, like Delphinus and Sagitta,
contains no stars of importance. Beta Trian-
guli is of the third magnitude, and Alpha of
the fourth.

Next to Andromeda, Triangulum, and Aries,
and to the left of these groups we come to the

THE SOUTHERN STARS. 95

constellations of Perseus and Taurus, discussed
in the chapter on the .winter constellations.
These fine groups come into prominence in
the autumn, but it is in winter that they reach
their most favourable position for observation.

CHAPTER VII.

THE SOUTHERN STARS.

A distinguished writer on astronomy has
remarked that " there is a strange unforget-
table sensation in the first voyage from our
high northern latitudes to the southern hemi-
sphere. Besides the disappearance of old
friends and the coming into sight of stranger
stars, the known stars that still remain to us
adopt most unfamiliar attitudes, and these
become more and more perplexing the further
south we go." In other words, a considerable
number of the constellations visible in these
latitudes are invisible in Australia, South
Africa and South America, while the constella-
tions which are visible here are seen inverted.
As was seen in the preceding chapters, a
considerable number of stars visible in the
northern hemisphere do not set. On every
clear night we are able to see the Plough,
Cassiopeia, the Pole Star and other notable

96 PKACTICAL ASTKONOMY.

stars and constellations. A number of stars
are visible to us in their different seasons,
such as Orion, Leo, Virgo, and generally
speaking, the constellations of the Zodiac ;
while a considerable number of star-groups are
totally invisible to us in the north, because
they do not rise above our horizon. These
are the southern circumpolar stars. Seen from
the southern hemisphere, these stars do not
set ; they occupy the same position to the
inhabitants of the southern lands as the north-
ern circumpolar stars do to us. To the dwellers
in Australia, South Africa and South America,
the Plough, Cassiopeia, and other northern
star-groups are quite invisible ; on the other
hand, Orion, Pegasus and the constellations of
the Zodiac are visible from both hemispheres.

The southern sky may be divided into two
portions — a portion rich in stars and a portion
poor in stars.

We may conveniently begin with Scorpio, a
constellation which, as was noted in a previous
chapter, is not seen to advantage in northern
latitudes. In the south Scorpio is seen in its full
magnificence high in the sky, almost exactly
overhead. Following the course of the Galaxy
— here very brilliant — we reach the constella-
tions Lupus, or the Wolf, and Ara, the Altar.
Lupus is a notable constellation, three of its
stars being brighter than the third magnitude.

THE SOUTHERN STARS. 97

Following the course of the Galaxy we come
to the three constellations, Centauries, or the
Centaur ; Crux, or the Cross ; and Argo Navis,
or the Ship Argo. These are three very famous
groups. Centaurus has ten stars brighter than
the third magnitude. Alpha and Beta, im-
mersed in the stream of the Milky Way, are of
the first magnitude, Alpha being indeed one
of the most brilliant stars in the sky, inferior
only to Sirius and Canopus in brilliance.

• <

Fig. 12. — Centaurus and Southern Cross.

Alpha Centauri is interesting as the nearest
of the stars. Its distance was measured in the
years 1831-2 by Thomas Henderson, Astron-
omer-Royal at the Cape of Good Hope, and
afterwards Professor of Astronomy in the
University of Edinburgh and Astronomer-
Royal for Scotland ; and in point of fact it
was the first star whose distance was success-
fully measured. It is distant about twenty-
five billions of miles from the Solar System.
It is also well known as a binary, or revolving

(2,015) 7

■98 PRACTICAL ASTRONOMY.

double star. Recently Mr. R. T. A. Innes, of
Johannesburg, has discovered a minute star at
about the same distance and probably con-
nected with the system of Alpha Centauri.
It is the faintest known star in the Universe,
its luminosity being only one ten-thousandth
that of the Sun.

Centaurus also contains other interesting
objects, notably the magnificent cluster Omega
Centauri.

The Southern Cross is a small constellation
in area, but it is a brilliant group, containing
three stars brighter than the second magni-
tude. It is thickly immersed in the stream of
the Galaxy, and is perhaps rendered more
noticeable by the wonderful gap in the Milky
Way known as the " coal-sack." There is in
the constellation Cygnus a rift in the Galaxy
which has sometimes been named the " north-
ern coal-sack," but the great gap in Crux has
been described as truly an awe-inspiring object
— a region in the midst of " clusters and beds
•of worlds," yet destitute of stars. Here we
seem to get a glimpse through the visible
Universe itself into that region which has been
designated the " darkness behind the stars."

Leaving the Cross, the Galaxy passes into
Argo Navis, a constellation so large that
astronomers found it necessary many years
ago to subdivide it into four smaller groups —

THE SOUTHEKN STARS. 99

Malus, or the mast ; Vela, or the sails ; Puppis,
or the stern, and Carina, or the keel. Argo
contains fifteen stars brighter than the third
magnitude, one of which is the well-known
Canopus. This orb is, with the exception of
Sirius, the brightest star in the sky, and its dis-
tance is so vast that it can only be estimated.

In this constellation too is situated Eta
Argus, the famous " link " between variable
and temporary stars. Originally an incon-
spicuous star, it was observed by Sir John
Herschel in 1838 to blaze up to the first mag-
nitude, when it equalled Aldebaran in bril-
liance. Five years later it equalled Canopus,
and was one of the most brilliant stars in the
sky. Since then the star has steadily de-
creased in magnitude, and now it is barely
visible to the unaided eye.

After leaving Argo, the galactic stream
passes into Canis Major, which is seen to
greater advantage in the southern latitude
than in the north ; this star-group, however,
was described in an earlier chapter.

We have described the course of the Galaxy
in the southern hemisphere ; in other words,
the rich region. The remaining portion of the
southern circumpolar heavens is very poor in
stars. The south celestial pole is situated in
the constellation Octans — a group very poor
in stars, containing no orb as bright as the

100 PRACTICAL ASTRONOMY.

fourth magnitude. The star nearest the south-
ern pole is Sigma Octanis, of the sixth magni-
tude, just visible to the unaided eye ; so there
is no south pole star in the true sense of the
word. Round Octans are a number of star-
groups equally inconspicuous — Pavo, Mensa,
Dorado, Hydrus, Toucan, Apus, &c. The
paucity of bright stars is relieved by the
presence of the two remarkable objects vari-
ously known as the " Magellanic Clouds,"
" the Clouds of Magellan," and the " Nubec-
ulae." These two objects are peculiar to the
southern hemisphere, and have no counterpart
in our northern skies. They are composed of
stars, star-clusters and nebulae, and seem to
form independent systems outside of the
greater universe of stars.

On the opposite side of the pole from the
Cross is the constellation Eridanus, the north-
ern part of which is to be seen in our latitudes.
Its most brilliant parts, however, are only
visible in the south. Its most brilliant star,
Alpha, is also known by the Arabic name of
" Achernar," " the end of the river." Finally,
between Argo and Eridanus is Columba, the
Dove, immediately south of Lepus, the little
group below Orion.

A number of these southern constellations
such as Argo, Centaurus, Lupus, and Eridanus
have been known from prehistoric times ;

SUN, MOON, AND PLANETS. 101

but the majority have only been known and
named since European civilisation reached
the southern hemisphere. Considering the
advantages of later astronomers as compared
with the circumstances of the early star-
gazers who named our northern star-groups,
it cannot be pretentied that they accomplished
their work satisfactorily ; for the southern
constellations, speaking generally, are not only
difficult to identify, but are inappropriately
named and grouped.

The chief stars in the southern hemisphere
are easily remembered, in the same way as
those in the north — the Cross and Achernar are
at different sides of the Pole ; so are Argo and
Scorpio. And with the march of the seasons
their positions are constantly changing.

CHAPTER VIII.

SUN, MOON, AND PLANETS.

We have now discussed the various constella-
tions and the best method of recognising them
and identifying their principal stars. These
stars lie at immense distances from the Earth ;
they form the background of the motions of
the bodies of the Solar System.

The ancient Greeks recognised seven bodies

102 PRACTICAL ASTRONOMY.

which were clearly not stars — the Sun, the
Moon, Mercury, Venus, Mars, Jupiter, and
Saturn. All the stars which the ancients
grouped into constellations were known to be
fixed in position relatively one to the other.
Sun, Moon, and planets were known to move
round the starry sphere, and to have different
motions. Indeed, the word " planet " is Greek
for " wanderer." While the solar and lunar
motions are regular, the planets obviously
wander round tho heavens.

The Zodiac. — We may briefly consider the
apparent motions of the Sun and Moon, and of
the various planets, and also the best method
of identifying the " wandering stars." The
ancients recognised the fact that Sun, Moon,
and planets moved round the heavens within
a belt of sky which they termed the Zodiac,
and which passed through the twelve con-
stellations, Aries, Taurus, Gemini, Cancer, Leo,
Virgo, Libra, Scorpio, Sagittarius, Capricornus,
Aquarius, and Pisces.

The Sun. — The position of the Sun in the
heavens is not so obvious as that of the Moon
and planets ; but astronomers in prehistoric
times were aware of the fact that the Sun
moved round the sky in a path called the
ecliptic, reaching right through the zodiacal
constellations. In the chapters on the stars
in their seasons we saw that some of the

SUN, MOON, AND PLANETS. 10$

zodiacal constellations such as Taurus and
Gemini are high in the heavens, and others
such as Scorpio and Sagittarius are low down
and not far above the horizon. Here, then,,
we have the key to the seasonal changes.
When the Sun in its apparent path is in the
high constellations of the Zodiac it is summer ;.
the orb of day is high above the horizon and is-
visible for a protracted period ; when, on the
other hand, the Sun is in Scorpio or Sagittarius
it is winter. The Sun is low in the sky and is
only visible for a comparatively short time.
When the brilliant constellations of winter
are on the meridian at midnight, the Sun is.
in the zodiacal constellations opposite, namely,
the " summer star-groups,'' Scorpio and Sagit-
tarius. In summer the Sun is in the winter
constellations. The reason of this tilting of the
ecliptic is the fact mentioned in the first
chapter, namely, that the axis of the Earth is
not perpendicular to the plane of its orbit, but
inclined twenty-three degrees. At the spring
equinox, in March, day and night are equal
all over the Earth — at the poles and the
equator. At this period both the poles are
exposed to the Solar days in an equal degree ;
but with the gradual revolution of the Earth
in its orbit the northern hemisphere is inclined
more and more to the solar beams, and the
southern hemisphere less and less. Gradually

104 PRACTICAL ASTRONOMY.

spring passes into summer. At the summer
solstice in June the days are much longer than
the nights in the northern hemisphere, while
in the southern the reverse state of things
prevails. After June the period of daylight
in the northern hemisphere gradually de-
creases until in September day and night are
equal all over the globe. The axis of the
Earth is again upright relative to the Sun ;
the northern hemisphere is tilted more and
more away from the Sun as autumn passes
into winter, until at the winter solstice it
reaches its greatest inclination away from the
sun — the reverse state of affairs being the case
in the south. After the winter solstice the
period of daylight gradually increases, as the
Earth is tilted more and more towards the
solar beams until the spring equinox in March,
when day and night are equal all over the globe.
The result of this cycle of change is that in
spring and autumn the Sun rises due east and
sets due west ; in summer it rises in the north-
east and sets north-west, and is about eighteen
hours above the horizon — just as is the case
with the high constellations of the Zodiac,
Taurus and Gemini ; in winter it rises in the
south-east and sets in the south-west, and is
above the horizon for a comparatively short
time, as in the case of the low constellations
of the Zodiac, Scorpio and Sagittarius.

SUN, MOON, AND PLANETS. 105

The seasons, then, are due to the inclination
of the Earth's axis. But another cause is also
at work, though in a very modified degree.
The Earth's orbit is not a perfect circle, but
an ellipse ; therefore at one point of its orbit
the Earth is closer to the Sun than at the other.
In our northern winter the Earth is three
millions of miles nearer than in summer.
Here we have an apparent paradox — that the
time of closest approach to the Sun is the
time of greatest cold. When we consider the
question, the apparent paradox soon dis-
appears. In the northern hemisphere the
lesser distance of the Sun modifies the rigours
of winter, and its greater distance mitigates
the warmth of summer. In the southern
hemisphere, on the other hand, the conditions
are reversed. The period of greatest heat
occurs when the Sun is at its least distance,
and that of greatest cold when it is furthest
away. Thus the climate in the northern
hemisphere is rendered more equable than
that in the southern.

To the observer without a telescope the Sun
can scarcely be described as an interesting
object. When spots are numerous, at the
sun-spot maximum, the larger ones are some-
times visible to the unaided eye through
smoked glass. But the visibility of sun-spots
to the unaided eye is a very rare occurrence.

106 PRACTICAL ASTRONOMY.

With a small telescope provided with a dark
eyepiece many interesting observations on
spots — isolated and in groups — may be made.
To the observer provided with such an in-
strument the Sun is a fascinating study.

The Moon. — The motion of the Sun round
the heavens is only apparent. It is the Earth
which moves along the ecliptic and causes the
apparent motion of the orb of day. With the
Moon the case is different. Alone of all the
celestial bodies the Moon really revolves round
the Earth. Its circuit of the zodiacal con-
stellations represents a true motion. This
circuit occupies 29 days and over 12 hours,
roughly a month. In reality the Moon's
period of revolution round the Earth is 27 days
7 hours. The difference between the real and
apparent periods is due to the Earth's revolution
round the Sun. carrying the Moon along with it.

The phases of the Moon have been noted
from the earliest ages ; they are due to the
fact that the Moon is a dark body shining by
reflected light. At " new Moon " the Earth,
the Moon, and the Sun are in a straight line,
with the Moon in the middle position. The
Sun is shining direct on the side of the Moon
which is turned away from the Earth, and our
satellite is invisible. At " first quarter " we
only see half of the Moon illuminated. It is
then at the point of its orbit, midway between

SUN, MOON, AND PLANETS. 107

"new Moon" and "full Moon." At full
Moon the Sun, the Earth, and the Moon are in
a straight line, with the Earth in the middle
position. The Sun is shining directly on the
Moon, and we see it fully illuminated, while
at " last quarter " only half of the Moon is
illuminated, as seen from Earth.

Owing to its eastward motion along the
Zodiac, the Moon rises about 50 minutes later
each day. This is the average amount of
delay, but the amount varies ; sometimes it
is less than half an hour, sometimes an hour
and a quarter. The difference depends on the
angle which the Moon's path makes with the
horizon ; this angle is least in the constellation
Pisces, visible in autumn. Hence we have the
phenomenon of the " Harvest Moon," when
our satellite rises less than half an hour later
every evening.

There is much less moonlight in summer
than in winter. At first this may seem to be
due to the lengthened period of daylight —
the moonlight not being required and con-
sequently not noticed ; such, however, is not
the case. There is really less moonlight in
summer than winter. This arises from the
fact that before the Moon can be " full " and
shining with complete radiance, it must be
*' in opposition " to the Sun ; that is, situated
in the diametrically opposite region of the sky.

108 PRACTICAL ASTRONOMY.

In winter the Sun is passing through the lower
zodiacal constellations, consequently the Moon
at the full phase passes through the higher.
The full Moon at midwinter is in the same
situation as the Sun at midsummer. Thus in
winter there is more moonlight than sunlight.
In summer the conditions are reversed. The
Sun is in the higher constellations ; conse-
quently the full Moon at midsummer occupies
the place of the Sun at midwinter, and thus
there is more sunlight than moonlight.

The Moon may be studied by means of the
binocular, and even in a small telescope it is
a wonderful spectacle.

The full phase of the Moon is the most useful
to mankind, but it is not the most interesting
to the astronomer. At that phase the Sun is
shining direct on the Moon, and consequently
the objects of the lunar surface cast no shadows.
A view of the full Moon in a telescope is dis-
tinctly disappointing. A few days before the
full phase useful observations may be made.
The astronomer, however, studies the Moon at
all its phases ; in fact, it is only by long-
continued observation that anything can be
learned concerning our satellite.

When one looks at the Moon through a
telescope — large or small — for the first time,
the most striking feature is the rugged and
mountainous character of the lunar surface.

SUN, MOON, AND PLANETS. 109

The surface is diversified by great grey plains,
which were once supposed to be seas, and
mountainous uplands, comprising ranges of
hills and mountains, and great numbers of
walled plains and volcanic craters. These
volcanic craters are by far the most numerous
objects on the Moon. Volcanic action seems
to have been much stronger on our satellite
than our Earth — relatively to size. However,
this action seems to be now practically extinct,
and the Moon is generally believed to be a dead
world. Professor Pickering's studies indicate
the possibility that a very thin atmosphere
does exist, and that there is a rudimentary
vegetation. But, even if this be so, we are
correct in regarding the Moon as dead.

The Planets.— There can be little difficulty
in identifying the principal planets — Venus,
Mercury, Mars, Jupiter, and Saturn. Of the
seven chief planets of the Solar System outside
of our own world, only these five are visible
to the unaided eye. Uranus is practically
invisible without the aid of a telescope, and
Neptune absolutely so.

Absolutely the larger planets are divided
into two groups according to size — the Inner
Planets, comparatively close to the Sun, Mer-
cury, Venus, the Earth, and Mars, compara-
tively small in size ; and the Outer Planets —
beyond the ring of minor planets — Jupiter,

110 PRACTICAL ASTRONOMY.

Saturn, Uranus, and Neptune, planets of large
size. At present, however, we are discussing
the heavens as they appear to us ; we are
inhabitants of one of these inner planets, the
Earth. Consequently the planets appear to
us to be divided into two groups — those which
revolve round the Sun in orbits within the
Earth's pathway, and those revolving without.
These two groups are generally spoken of as
the " inferior " and " superior " planets. In
reality the more correct names are, the interior
and exterior planets. The interior planets are
Mercury and Venus, and the exterior planets
Mars, Jupiter, and Saturn — Uranus and Neptune
being beyond the reach of the unaided vision.
The two groups of planets have many points
of difference. The interior planets, Venus and
Mercury, are never seen far from the Sun.
They can never be in " opposition " ; that is
to say, they never rise at sunset, reach the
meridian at midnight and set at sunrise.
Neither is ever seen on an absolutely dark
sky ; they seem to oscillate to and fro on
either side of the orb of day. The exterior
planets on the other hand are to be seen in all
parts of the heavens ; they may be in " con-
junction," invisible in the solar beams, or in
" opposition," on the meridian at midnight
and visible all night. Thus there are many
more opportunities for observing the exterior

SUN, MOON, AND PLANETS. Ill

planets and their motions among the stars.
These motions are much less simple than those
of the Sun and Moon. The motion of the Sun
along the ecliptic is simply the Earth's motion
reflected in the heavens ; the Moon's circuit
of the Zodiac is simply the actual revolution
of the Moon round our world. But the
planetary motions are a combination of real
and apparent movements. The Earth is a
planet, and in motion round the Sun ; the
planets are also moving round the Sun. Hence
the Earth's motion is partly reflected in the
irregularities of the planetary motions. Thus
the planets are sometimes apparently moving
from west to east ; sometimes from east to
west. Sometimes they appear almost sta-
tionary. It is, however, no part of our present
purpose to enter into a discussion of the
planetary motions and their irregularities,
which have attracted the attention of astron-
omers and mathematicians in all ages.

Venus is the most brilliant planet — " the
evening star " and " the morning star," the
".Hesperus" and "Phosphorus" of the
Greeks. From very early times the identity
of the morning star and the evening star has
been recognised. The late Professor Schia-
parelli suggests that it was recognised so long
ago as the epoch of the Book of Job ; he be-
lieves " Mazzaroth in its season " to refer to

112 PKACTICAL ASTKONOMY.

the periodical appearances of Venus. Be this
as it may, the motions of Venus have been
familiar to mankind from the earliest ages.

Venus is said to be at superior conjunction
when the Earth, the Sun, and Venus are in
a straight line, with the Sun in the middle.
Venus, owing to its position within the Earth's
orbit, exhibits phases similar to the Moon, and
at this time it is fully illuminated, but is lost
in the rays of the Sun. Then the planet
emerges from the sunlight as " evening star."
When it reaches the position known as " great-
est elongation east " of the Sun, the disc seen
through a small telescope is fully illuminated
like the Moon at the quarters. As Venus
draws nearer to the Earth the disc increases
in size, but the illuminated portion decreases
until the planet — now a dwindling crescent —
is again lost in the rays of the Sun at the posi-
tion known as " inferior conjunction." This
position is analogous to "new Moon." The
planet is invisible, as its dark side is turned
towards the Earth. Shortly after this it
reappears as a " morning star " ; it is at first
a thin crescent, increasing in size until it
reaches the position known as " greatest
elongation west." It is now at its best posi-
tion for observation as a morning star. Seen
through the telescope the disc becomes smaller
and more fully illuminated, until it again

SUN, MOON, AND PLANETS. 113-

reaches " superior conjunction," and is lost in
the solar rays. The interval from conjunc-
tion to conjunction — superior conjunction to
superior conjunction, or inferior to inferior —
is 584 days, and is known as the " synodic
period " of Venus.

Venus at times is exceptionally brilliant, and
the ignorant have from time to time regarded
the planet as a return of the " star of Beth-
lehem," or as a portent. The phases of the
planet are not visible to the unaided eye, but
may be seen in a small telescope. These phases
were discovered by Galileo three centuries ago
with the newly-invented telescope. As a tele-
scopic spectacle Venus is one of the most ex-
quisite in the heavens, but owing to its thick
atmosphere and the difficulty of observing it,
little is known of its physical constitution.

Mercury' passes through the same series of
changes as Venus in a shorter time, its synodic
period being 116 days. Like Venus, Mercury
exhibits " phases," but these are not visible
in the smallest telescopes. Mercury is very
difficult of observation, and it is no small
tribute to the skill and perseverance of the
prehistoric astronomers that Mercury was
known in those early times. The planet is
never far from the Sun, and can only be seen
at its elongations as morning or evening star.
Even at these periods it is difficult to observe,.

(2,015) 8

114 PRACTICAL ASTRONOMY.

and is only to be seen when the horizon is
absolutely clear and free from clouds. It is
recorded that Copernicus never succeeded in
seeing the planet, although he often tried ;
the explanation of his failure being that he
lived on the banks of the Vistula, where the
horizon is never free from the mists which
rise from the river.

The exterior planets — Mars, Jupiter, and
Saturn — are to be seen in all parts of the
Zodiac. None of them are so bright as Venus,
but all are very noticeable. It is impossible
to mistake or confuse them. Jupiter, gener-
ally the superior of Mars, shines with a clear
steady yellow light ; at times, however, Mars
at its near approaches to the Earth is equal
to Jupiter in brilliance. It shines with a
steady fiery red light, from which peculiarity
it was termed " the planet of war " by the
ancients. Saturn, fainter than Mars or Jupiter,
is equal in brilliancy to a star of the first
magnitude ; it shines steadily with a dull
yellow light. All three planets are to be seen
in " opposition " to the sun when they rise
at sunset and set at sunrise ; and as they
make their nearest approaches at opposition,
they have been closely studied both in tele-
scopic and pre- telescopic times.

The synodic period of Jupiter — from con-
junction to conjunction or opposition to oppo-

SUN, MOON, AND PLANETS. 115

sition — is 399 days, and of Saturn 378 days.
Thus the farther off a planet is, the shorter is
its synodic period. With Mars the case is
different ; the synodic period is 780 days, over
two years. Mars is much closer to the Earth
than Jupiter and Saturn, and its apparent
motion is more complex. Oppositions of Mars,
too, vary greatly in brilliance. The orbit of
Mars is very elliptical in comparison with other
planetary orbits. The pathways of Mars and
the Earth approach nearest at the point occu-
pied by the Earth about the end of August,
and they diverge most at the point occupied
by our world in February. Hence when Mars
is in opposition in autumn it is very bright,
and in spring much fainter. This, however, is
somewhat modified by the fact that in spring
the planet is in the high zodiacal constellations,
and in autumn in the low star-groups. Favour-
able oppositions, and also unfavourable, recur
at intervals of about fifteen years. Thus there
were very favourable oppositions, when the
planet was very brilliant, in 1877, 1892, and
1907, and unfavourable appearances in 1886,
1901, and 1916.

A small telescope will show the satellites of
Jupiter and the ring of Saturn. It has been
alleged that the satellites of the former planet
have been seen with the unaided eye, but the
evidence is far from conclusive. In a small

116 PRACTICAL ASTRONOMY.

telescope, however, they are easily seen, and
form a beautiful telescopic spectacle. A small
instrument will, however, show no features
on Mars ; a good telescope is required to
show the surface-markings, while the famous
" canals " are only to be seen with powerful
instruments in favourable climates.

CHAPTER IX.

ASTRONOMICAL PHENOMENA.

Under the head of astronomical phenomena
we include occurrences and appearances in the
heavens — eclipses of the Sun and Moon, tran-
sits of Venus and Mercury, comets, meteors,
the zodiacal light, and the Aurora Borealis.
Such appearances attract a large amount of
attention — more, perhaps, than is their due.

Eclipses and Transits. — These kindred phe-
nomena are due to the fact that every body
in the universe shining by reflected light casts
a shadow into space in a direction opposite to
the source of illumination. Thus the Earth
casts a shadow, and similarly Venus, Mars,
Jupiter, and the other planets cast shadows.
The shadows cast by the Earth and the Moon
are the cause of the phenomena known as
solar and lunar eclipses. The Earth casts a

ASTKONOMICAL PHENOMENA. 117

shadow, and when the Moon, the Earth, and
the Sun are in a line, with our world in the
middle, the terrestrial shadow which extends
beyond the orbit of the Moon falls in the
direction of our satellite. If the pathway of
the Moon were exactly in the same plane or
level as that of our world, it would pass through
the shadow every time it reached the position
known as full Moon.

As a matter of fact, however, the Moon's
orbit is not exactly in the same plane as that
of the Earth, and only occasionally an eclipse
does take place. Sometimes a lunar eclipse is
total — that is to say, the Moon is completely
immersed in the Earth's shadow — and some-
times only partial, a portion of the disc re-
maining outside the true shadow. A total
eclipse of the Moon is a very remarkable and
beautiful phenomenon. As the Moon becomes
gradually immersed in shadow, the illuminated
portion becomes smaller and smaller until it
completely disappears. The Moon is not, how-
ever, usually totally invisible. It generally
assumes a dark copper-coloured hue, due to the
refraction of sunlight through the atmosphere
of the Earth. This is supposed to be due to
the fact that the blue rays of the Sun are
absorbed in traversing the atmosphere of the
Earth, just as the sunset and sunrise skies
assume a ruddy colour.

118 PEACTICAL ASTRONOMY.

Eclipses of the Sun take place at new Moon,
when the Earth, the Moon, and the Sun are in
a straight line, the Moon occupying the middle
position. Sometimes the shadow of the Moon
falls on our planet. This shadow is much
smaller than the shadow of the Earth, and it
only covers a small strip of territory on the
globe ; to observers within this strip the Sun
is for a few minutes totally eclipsed. Outside
this strip there is a partial eclipse, part of the
solar disc being obscured by the Moon. Occa-
sionally an eclipse is partial without being total
at any part of the Earth's surface. At times
an eclipse is " annular," when the Moon is at
the farthest point of its orbit and does not
appear large enough to cover the Sun. At
such times we are an " annulus " or ring of
light round the Moon's disc. Of these three
kinds of eclipses only total eclipses are useful
to astronomers. This is owing to the fact that
at such times the disc of the Moon appears
large enough to cover the Sun, but not large
enough, fortunately for astronomical science,
to hide from view the immediate vicinity of
the orb of day.

Since the days of the early Chaldeans astron-
omers have been familiar with a period by
which the recurrence of solar and lunar eclipses
can be predicted. This is known as the Saros.
Its length is 18 years 111 days. In the words

ASTRONOMICAL PHENOMENA. 119

of an American astronomer, " At the end of
this period the centres of the Sun and Moon
return very nearly to their relative positions
at the beginning of the cycle ; also certain
technical conditions relating to the Moon's
orbit and essential to the accuracy of the saros
are fulfilled." Thus a total solar eclipse took
place on May 17, 1882 ; it recurred on May 28,
1900 ; and again on June 8, 1918. Eclipses,
however, do not recur on the same part of
the Earth's surface ; hence at any given place
total solar eclipses are very rare. There has
not been a total solar eclipse in the United
Kingdom since 1724, and there will not be one
visible until 1927. For those who have never
seen a total eclipse, the following description
by an American writer, Mrs. Todd, is worth
reading, as illustrating the magnificence of the
spectacle : " With frightful velocity the actual
shadow of the Moon is often seen approaching,
a tangible darkness advancing almost like a
wall, swift as imagination, silent as doom. The
immensity of Nature never comes quite so near
as then, and strong must be the nerve not to
quiver as this blue-black shadow rushes upon
the spectator with incredible speed. Some-
times the shadow engulfs the observers
smoothly, sometimes apparently with jerks ;
but all the world might well be dead and cold
and turned to ashes. Often the very air seems

120 PRACTICAL ASTRONOMY.

to hold its breath for sympathy ; at other
times a lull suddenly awakens into a strange
wind, blowing with unnatural effect. Then out
upon the darkness, gruesome but sublime,
flashes the glory of the incomparable corona,
a silvery, soft, unearthly light, with radiant
streamers, stretching at times millions of un-
comprehended miles into space, while the rosy
flaming protuberances skirt the black rim of
the Moon in ethereal splendour. It becomes
ouriously cold, dew frequently falls, and the
chill is frequently mental as well as physical.
Suddenly, instantaneous as a lightning flash,
an arrow of actual sunlight strikes the land-
scape, and Earth comes to life again, while
corona and protuberance melt into the return-
ing brilliance."

Transits are kindred phenomena to eclipses.
Only the interior planets, Mercury and Venus,
are to be seen in transit across the Sun. Tran-
sits occur, like solar eclipses, when our world,
Venus, and the Sun, or our world, Mercury,
and the Sun are in a straight line. There is
no eclipse, owing to the small apparent size of
Mercury and Venus ; we merely see black discs
as spots crossing the face of the Sun.

Transits of Venus occur in pairs, separated
by intervals of eight years ; and the pairs are
separated by intervals of 105 J and 121 J years.
There were transits in 1631 and 1639, 1761

ASTRONOMICAL PHENOMENA. 121

and 1769, 1874 and 1882; and the next pair
will take place in 2004 and 2012. Transits of
Mercury are much more frequent.

Comets and Meteors. — These kindred celes-
tial bodies have attracted the attention of
mankind from the earliest ages. Among the
ancients and to the people of the Middle Ages
comets were a source of terror, and were
believed to be terrible portents of wars, fam-
ines, and other national disasters.

In the present day these feelings have given
place to wonder and admiration. Of all celes-
tial phenomena, comets attract the great-
est and most widespread attention. In our
present knowledge we may divide comets
into two classes — those which have been
proved to revolve round the Sun and whose
returns can be predicted, and those comets
which have not been demonstrated to be
members of the Sun's family. To the first
class belongs the famous comet of Halley,
whose last appearance in 1910 fell so far short
of popular expectation ; and also the faint
comet of Encke, which returns every three
years, and others. Most of the periodic
comets are faint, and do not attract atten-
tion even when visible to the unaided eye.

The brilliant comets of 1811, 1843, and 1858,
and other notable comets of the last century,
may or may not belong to the Solar System ;

122 PRACTICAL ASTRONOMY.

if they revolve round the Sun, they must do
so in enormously long periods. Thus a bright
comet appears, unexpectedly as a general
rule ; its coming has not been predicted. This
was the case with the only bright comet of
recent years, the " great Daylight Comet " of
January 1910.

Meteors or shooting-stars are generally be-
lieved to be the products of the dissolution
of comets — minute particles of matter which
become ignited on entering the Earth's atmos-
phere. They travel in ones, twos, threes, and
in swarms or streams. The chief streams are
the Leonids, Perseids, Lyrids, Andromedids,
&c. ; but there are many others, and not a
night passes without several meteors shooting
across the sky.

The study of meteors is one peculiarly
adapted for the observer without a telescope ;
indeed, in this branch of astronomy both
telescope and binocular are useless. All our
knowledge of meteors is due to observation of
meteors — time of flight, length of path, bril-
liance, colour, &c. — by the unaided eye ; and
the greater part of the work in this branch of
astronomy has been accomplished by one non-
professional astronomer — Mr. W. F. Denning
of Bristol.

A remarkable fact in connection with meteors
is that from midnight to dawn is a much more

ASTRONOMICAL PHENOMENA. 123

favourable time for observation than from
sunset to midnight. The explanation is that
more meteors meet the Earth than overtake
it, and as Mr. Maunder remarks — " the Earth
has its sunrise point in front as it moves for-
ward in its orbit, its sunset point behind."

The Zodiacal Light. — This is a phenomenon
which is much better seen in tropical than in
temperate regions, but it is occasionally ob-
served in Europe. A pearly glow is sometimes
noticed in the spring to spread over a portion
of the sky where the Sun has disappeared. In
autumn the same phenomenon is also to be
seen before sunrise. It is in tropical regions,
however, that it is seen in its full glory.
Instead of being seen like a cone, as in our
latitudes, it appears as a band of light, and the
portions near to the Sun seem as brilliant as
the Galaxy. The exact nature of the zodiacal
light has long been more or less of a mystery.
The general idea among astronomers is that
it is due to diffused dust, in all probability
meteoric matter which forms an outer append-
age to the Sun. Opposite in the heavens to
the Light is a much fainter phenomenon known
by its German name of " the Gegenschein," or
counter-glow. Probably it is also of meteoric
composition.

The Aurora Borealis. — This phenomenon,
closely connected with the magnetism of the

124 PRACTICAL ASTRONOMY.

Earth, is one of the most striking of celes-
tial spectacles. Properly speaking, the aurora
should perhaps be classed among atmospheric
phenomena, but its close connection with the
sun-spot period renders it more directly akin
to the heavens proper.

The Aurora Borealis — bhe "Northern Lights"
— is a regular phenomenon in the Arctic
regions, and is often visible in the Shet-
lands and Orkneys, the north of Scotland,
and Northern Europe. In lower latitudes the
aurora is a rare spectacle, and attracts
a great deal of attention. It consists of
streamers, bands, curtains, and rays of light
of varying tints and different degrees of bril-
liancy. These tremble and shoot up and down
the sky with startling effect ; hence the popular
name of the aurora — " the Merry Dancers."

In lower latitudes aurorae should be looked
for more particularly when spots are numerous
on the solar disc. Great storms in the Sun
are generally accompanied by magnetic dis-
turbances and brilliant auroral displays on the
Earth. The nature of the connection has not
been fully explained, but of its reality there is
no doubt.

In this chapter particular attention has been
given to these astronomical phenomena which
are of comparatively rare occurrence — the
appearance of bright comets, meteoric dis-

ASTRONOMICAL PHENOMENA. 125

plays, eclipses of the Sun and Moon. These
phenomena never fail to awaken the curiosity
and interest of the average man. It is well
that they should ; and yet it is necessary to
remember that wonderful as are eclipses, re-
markable as are meteoric showers, far more
wonderful, far more marvellous are the or-
dinary facts which astronomy teaches us, far
more awe-inspiring is a thoughtful glance into
the immeasurable heavens. The marvellous
power and energy of the Sun, the never-failing
regularity of the Moon and planets in their
eternal revolution, the vast distances and
spaces, the calm shining of the changeless stars
— these are marvels visible to us daily and
nightly, and we heed them not. Familiarity
gives rise, if not to contempt, at least to in-
difference. As Emerson has truly said : "If
the stars should appear one night in a thousand
years, how would men believe and adore, and
preserve for many generations the remembrance
of the City of God which had been shown."

BIBLIOGRAPHY.

The Constellations and How to Find Them. By
William Peck, F.R.A.S. A series of monthly charts
showing the chief stars and their position in the
heavens. A useful guide for the beginner. (Gall &
Inglis, Edinburgh.)

Star-Groups. By J. Ellard Gore, F.R.A.S. A
more advanced book than the last-named. There
is a map for each constellation, and the individual
stars are plainly marked. Probably the best book
of its kind. (Crosby, Lockwood & Co., London.)

Astronomy Without a Telescope. By E. Walter
Maunder, F.R.A.S. A work descriptive of the
heavens as seen with the unaided eye. The first part
of the book describes the constellations season by
season. The second and third parts describe ex-
ercises and practical observations. An excellent
work. (" Knowledge " Office, London.)

A Popular Introduction to Astronomy. By Rev.
A. C. Henderson. A little book by an amateur
astronomer, who has worked out for himself the
exercises in astronomy which he describes. (Manson,
Lerwick, Shetland.)

A New Astronomy. By Professor D. P. Todd.
More advanced than the preceding books and less
purely descriptive of the heavens, as they are. This
work is most helpful to those beyond the stage of
merely looking at and identifying the stars. (Samp-
son, Low & Co., London.)

Astronomy for Amateurs. By Camille Flammarion.
This book is rather an astronomical survey than a
guide to the heavens ; but it contains some chapters
bearing on this branch of the subject. (Fisher
Unwin, London.)

INDEX.

Alcor, 28.

Alcyone, 46.

Aldebaran, 7, 21, 44, 45, 53, 64,

66, 99.
Al Fard, 61.
Algol, 50, 51, 91.
Altair, 87.

Anderson, T. D., 52.
Andromeda, 37, 92, 93, 94.
Antares, 77.

Aquarius, 89, 90, 92, 102.
Aquila, 79, 81, 86, 87, 88.
Ara, 96.

Arcturus, 66, 67, 68, 69.
Argo Navis, 97, 98, 99, 100, 101.
Aries, 19, 91, 102.
Auriga, 33, 37, 47.
Aurora Borealis, 116, 123.

Ball, Sir R. S., 80.
Barnard, E. E., 75.
Bellatrix, 41.
Betelgeux, 39, 40, 42, 43, 45, 54,

64, 77.
Bootes, 8, 64, 67, 69, 70, 75.

Cancer, 61, 62, 102.

Canes Venatici, 62.

Canis Major, 21, 38.

Canis Minor, 43.

Canopus, 97, 99.

Capella, 32, 33, 35, 48, 54, 64, 79.

Capricornus, 88, 89, 102.

Carlyle, T., 8.

Cassiopeia, 29, 30, 31, 32, 33,

34, 52, 95.
Castor, 46, 47.
Centauri, Alpha, 20, 75, 97.
Centaurus, 20, 97, 98, 100.
Cepheus, 34, 35.
Ceres, 15.
Cetus, 90, 91.
Coma Berenices, 62.
Comets. 15, 16, 121, 122.
Copernicus, N., 114.

Cor Caroli, 63.

Corona Borealis, 64, 70.

Corvus, 60.

Crater, 60, 61.

Cross, the Southern, 96, 98.

Cygni (61), 84, 85.

Cygnus, 8, 19, 81, 83, 85, 87, 98.

Delphinus, 88, 94.
Deneb, 84.

Denning, W. E., 122.
Draco, 8, 35.
Dyson, Sir F. W., 22.

Earth, 10, 11, 13, 14, 15, 20, 21,
22, 23, 24, 57, 81, 82, 85, 86,
101, 103, 104, 105, 109, 110,
111, 112, 116, 117, 118, 124.

Eclipses, 116, 117, 118, 119.

Eddington, A. S., 22, 73.

Elkin, W., 68, 69.

Emerson, R. W., 125.

Encke, J. F., 121.

Eridanus, 47, 91, 100.

Flammarion, C, 22, 38.
Fomalhaut, 90.

Galaxy, the, 22, 30, 60, 64, 65,
78, 82, 83, 84, 85, 86, 87, 88,
96, 98, 99, 123.

Galileo, 113.

Gemini, 44, 46, 48, 61, 102, 103,
104.

Goodrick, J., 51.

Gore, J. E., 50, 65.

Hale, G. E., 12.

Halley, E., 121.

Henderson, T., 97.

Hercules, 71, 72, 73, 74, 75, 94.

Herschel, Sir J., 99.

Herschel, Sir W., 18, 35.

Hesiod, 17, 25, 45.

Homer, 17, 25, 42.

Hyades, the, 44.

Hydra, 61, 65.

128 INDEX.

Innes, R. T. A., 98.

Job, 17, 25, 42, 45.
Jupiter, 11, 15, 17, 18, 32, 102,
109, 114, 115.

Kapteyn, J. C, 22.

Leo, 6, 55, 56, 57, 62, 63, 65, 96,

102.
Lepus, 38, 47, 100.
Libra, 76, 102.
Lowell, P., 14.
Lupus, 96, 100.
Lyra, 33, 79.

Mars, 6, 11, 13, 14, 18, 77, 102,

109, 114, 115, 116.
Maunder, E. W., 5, 19, 30, 56,

69 90 123.
Mercury, 11, 13, 102, 109, 110,

112, 113, 120.
Meteors, 16, 57, 121, 122, 123.
Milky Way. See Galaxy.
Mirfak, 50.
Mizar, 28._
Montanari, 51.
Moon, the, 5, 10, 13, 16, 20, 23,

101, 102, 106, 107, 108, 109, 111,

116, 117, 118, 119, 120, 125.

Neptune, 11, 15, 110.
Newcomb, S., 80.
Nova Persei, 87, 88.

Ophiuchus, 71, 74.
Orion, 7, 8, 18, 37, 38, 39, 41, 43,
44, 45, 53, 54, 69, 77, 94, 96.

Pegasus, 92, 93, 96.
Perseus, 35, 37, 49, 50, 52, 95.
Pickering, W. H., 14, 109.
Pisces, 89, 90, 102.
Pleiades, 18, 45, 62.
Plough, the, 8, 25, 26, 27, 28,

29, 30, 32, 33, 34, 35, 45, 55,

63, 67, 95.
Pole Star, the, 28, 30, 35, 95.
Pollux, 46, 64.
Praesepe, 62.

Proctor, R. A., 85.
Procyon, 42, 43, 64.

Regulus, 56.

Richter, J. P., 24.

Rigel, 40, 41, 43, 47, 54, 64, 66.

Sagitta, 87, 94.

Sagittarius, 76, 78, 88, 102-104.

Saros, 118.

Saturn, 15, 102, 109, 114, 115.

Schiaparelli, G. V., 14, 111.

Scorpio, 38, 76, 77, 78, 88, 96,

101, 102, 103, 104.
Serpens, 71, 74, 75, 87.
Serviss, G. P., 69.
Shapley, H., 72, 73.
Shelley, P. B., 23.
Sirius, 7, 17, 19, 21, 43, 53, 64,

66, 97.
Solar System, the, 11, 16, 17,

18, 19, 22, 23, 41, 42, 85, 101,

121.
Spica, 68, 64.
Sun, the, 10, 12, 16, 21, 24, 40,

41, 43, 56, 69 81, 85, 102, 103.

104, 105, 106, 107, 108, 110, 111

113, 116, 117, 123, 124, 125.

Taurus, 21, 44, 48, 95, 102, 103,

104.
Tennyson, A., 44, 54.
Todd, Mrs., 119.
Triangulum, 94.
Tycho Brahe, 32.

Uranus, 11, 15, 110.
Ursa Major, 25, 28.
Ursa Minor, 29.

Vega, 32, 33, 35, 66, 68, 79.
Venus, 11, 13, 32, 102, 109, 110,

111, 112, 113, 120.
Virgo, 6, 58, 62, 63, 65, 96, 102.
Vogel, H. C, 51.

Wolf, M., 15.

Zodiac, 96, 102, 103, 104, 107,

111, 114.
Zodiacal Light, the, 123.

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