and easily recognized constellations in the heavens. This is the
constellation of Scorpio, The Scorpion, which will be found not far
above the southern horizon at this time. The small constellation
of Libra, The Scales, which lies just to the northwest of Scorpio,
was at one time a part of this constellation and represented the
creature's claws, but some centuries ago its name was changed to
Libra. Both Scorpio and Libra are numbered among the twelve zodiacal
constellations--that is, they lie along the ecliptic, or apparent
yearly path of the sun among the stars. Scorpio is the most brilliant
and interesting of all the zodiacal groups. The heart of the Scorpion
is marked by the magnificent first-magnitude star Antares, which is
of a deep reddish color. The name signifies Rival of Ares (Mars).
It is so called because it is the one star in the heavens that most
closely resembles Mars, and it might be mistaken for the ruddy planet
if one were not familiar with the constellations. At times, when Mars
is at a considerable distance from the earth, it is almost equal
in brightness and general appearance to this glowing red star in
the heart of the Scorpion. In its trips around the sun, Mars passes
occasionally very close to Antares, and the two then present a very
striking appearance.
[Illustration: JULY--LIBRA AND SCORPIO]
With a telescope of medium size, one will find an exquisite little
green companion-star close to Antares. The little companion is so
close to Antares that it is difficult to find it in the glare of
light from its more brilliant neighbor. Antares is one of the giant
stars of the universe. In fact it is, so far as we know, the greatest
of all the giants. Its diameter is more than five hundred times that
of our own sun and nearly twice that of the giant star Betelgeuze in
Orion. If placed at the center of the solar system its surface would
lie far beyond the orbit of Mars.
Both Ophiuchus and Scorpio are crossed by the Milky Way, that broad
belt of numberless faint stars that encircles the heavens. Some of
the most wonderful and beautiful regions of the Milky Way are to be
found in these two constellations.
At various times in the past, there have suddenly flashed forth
brilliant stars in the Milky Way which are known as "temporary
stars," or "novæ." These outbursts signify that some celestial
catastrophe has taken place, the nature or cause of which is not
clearly understood. Some of the most brilliant of these outbursts
have occurred in these two constellations. The life of a nova is very
short, a matter of a few months, and it rapidly sinks into oblivion,
so nothing is to be seen of some of the most brilliant of all these
stars that have appeared in this region in the past. A few are still
faintly visible in large telescopes.
IX
AUGUST
It was one of the twelve labors of Hercules, the hero of Grecian
mythology, to vanquish the dragon that guarded the golden apples in
the garden of the Hesperides. Among the constellations for July we
found the large group of stars that represents the hero himself,
and this month we find just to the north of Hercules the head of
Draco, The Dragon. The foot of the hero rests upon the dragon's head,
which is outlined by a group of four fairly bright stars forming a
quadrilateral or four-sided figure. The brightest star in this group
passes in its daily circuit of the pole almost through the zenith
of London. That is, as it crosses the meridian of London, it is
almost exactly overhead. From the head of Draco, the creature's body
can be traced in a long line of stars curving first eastward, then
northward, toward the pole-star to a point above Hercules, where it
bends sharply westward. The body of the monster lies chiefly between
its head and the bowl of the Little Dipper. The tail extends in a
long line of faint stars midway between the two Dippers, or the
constellations of Ursa Major and Ursa Minor, the tip of the tail
lying on the line connecting the Pointers of the Big Dipper with the
pole-star Polaris.
Draco, as well as Ursa Major and Ursa Minor, is a circumpolar
constellation in our latitude; that is, it makes its circuit of the
pole without at any time dipping below the horizon in latitudes
north of 40°. It is, therefore, visible at all hours of the night in
mid-latitudes of the northern hemisphere, but is seen to the best
advantage during the early evening hours in the summer months. There
are no remarkable stars in this constellation with the exception of
Alpha, which lies halfway between the bowl of the Little Dipper and
Mizar, the star at the bend in the handle of the Big Dipper.
[Illustration: AUGUST--DRACO AND LYRA]
About four thousand seven hundred years ago, this star was the
pole-star--lying even nearer to what was then the north pole of the
heavens than Polaris does to the present position of the pole. The
sun and moon exert a pull on the bulging equatorial regions of the
earth, which tends to draw the plane of the earth's equator down
into the plane of the ecliptic. This causes the "Precession of the
Equinoxes" and at the same time a slow revolution of the earth's axis
of rotation about the pole of the ecliptic. The north pole of the
heavens as a result describes a circle about the pole of the ecliptic
of radius 23-1/2° in a period of 25,800 years.
Each bright star that lies near the circumference of this circle
becomes in turn the pole-star sometime within this period. The star
Alpha, in Draco, had its turn at being pole-star some forty-seven
centuries ago. Polaris is now a little over a degree from the north
pole of the heavens. During the next two centuries it will continue
to approach the pole until it comes within a quarter of a degree
of it, when its distance from the pole will begin to increase
again. About twelve thousand years hence the magnificent Vega,
whose acquaintance we will now make, will be the most brilliant and
beautiful of all pole-stars.
Vega (Arabic for "Falling Eagle") is the resplendent, bluish-white,
first-magnitude star that lies in the constellation of Lyra, The Lyre
or Harp, a small, but important, constellation just east of Hercules
and a little to the southeast of the head of Draco. Vega is almost
exactly equal in brightness to Arcturus, the orange-colored star in
Boötes, now lying west of the meridian in the early evening hours.
It is also a near neighbor of the solar system, its light taking
something like forty years to travel to the earth. Vega is carried
nearly through the zenith of Washington and all places in the same
latitude by the apparent daily rotation of the heavens. It is a star
that we have no difficulty in recognizing, owing to the presence of
two nearby stars that form, with it, a small equal-sided triangle
with sides only two degrees in extent. If our own sun were at the
distance of Vega, it would not appear as bright as one of these faint
stars, so much more brilliant is this magnificent sun than our own.
The two faint stars that follow so closely after Vega and form the
little triangle with it are also of particular interest. Epsilon
Lyræ, which is the northern one of these two stars, may be used as a
test of keen eyesight. It is the finest example in the heavens of a
quadruple star--that is, "a double-double star." A keen eye can just
separate this star into two without a telescope, and with the aid of
a telescope, each of the two splits up into two stars, making four
stars in place of the one visible to the average eye. Zeta, the other
of the two stars that form the little triangle with Vega, is also a
fine double star. The star that lies almost in a straight line with
Epsilon and Zeta and a short distance to the south of them is a very
interesting variable star known as Beta Lyræ. Its brightness changes
very considerably in a period of twelve days and twenty-two hours.
This change of brightness is due to the presence of a companion
star. The two stars are in mutual revolution, and their motion is
viewed at such an angle from the earth that, in each revolution, one
star is eclipsed by the other, producing a variation in the amount
of light that reaches our eyes. By comparing this star from day to
day with the star just a short distance to the southeast of it, which
does not vary in brightness, we can observe for ourselves this change
in the light of Beta Lyræ. There are a number of stars in the heavens
that vary in brightness in the same manner as Beta Lyræ, and they are
called eclipsing-variable stars.
On the line connecting Beta Lyræ with the star southeast of it and
one-third of the distance from Beta to this star, lies the noted
Ring Nebula in Lyra, which is a beautiful object even in a small
telescope. It consists of a ring of luminous gas surrounding a
central star. The star shines with a brilliant, bluish-white light
and is visible only in powerful telescopes though it is easily
photographed since it gives forth rays to which the photographic
plate is particularly sensitive. In small telescopes the central part
of this nebula appears dark but with a powerful telescope a faint
light may be seen even in the central portion of the nebula. This is
one of the most interesting and beautiful telescopic objects in the
heavens.
It is in the general direction of the constellation of Lyra that our
solar system is speeding at the rate of more than a million miles a
day. This point toward which we are moving at such tremendous speed
lies a little to the southwest of Vega, on the border between the
constellations of Lyra and Hercules, and is spoken of as The Apex of
the Sun's Way.
[Illustration: AUGUST--SAGITTARIUS]
In the southern sky we have this month the constellation of
Sagittarius, The Archer, which is just to the east of Scorpio and
a considerable distance south of Lyra. It can be recognized by its
peculiar form, which is that of a short-handled milk dipper, with
the bowl turned toward the south and a trail of bright stars running
from the end of the handle toward the southwest. This is one of
the zodiacal groups which contain no first-magnitude stars, but a
number of the second and third magnitude. It is crossed by the Milky
Way, which is very wonderful in its structure at this point. Some
astronomers believe that here--among the star-clouds and mists of
nebulous light which are intermingled with dark lanes and holes, in
reality dark nebulæ--lies the center of the vast system of stars and
nebulæ in which our entire solar system is but the merest speck. Some
of the grandest views through the telescope are also to be obtained
in this beautiful constellation of Sagittarius, which is so far
south that it is seen to better advantage in the tropics than in the
mid-latitudes of the northern hemispheres.
X
SEPTEMBER
One of the most beautiful constellations of the northern hemisphere
is Cygnus, The Swan, which is in the zenith in mid-latitudes about
nine o'clock in the evening the middle of September. It lies directly
in the path of the Milky Way which stretches diagonally across
the heavens from the northeast to the southwest at this time. In
Cygnus, the Milky Way divides into two branches, one passing through
Ophiuchus and Serpens to Scorpio, and the other through Sagitta and
Aquila to Sagittarius, to meet again in the southern constellation of
Ara, just south of Scorpio and Sagittarius. On clear, dark evenings,
when there is no moonlight, this long, dark rift in the Milky Way
can be seen very clearly. In Cygnus, as in Ophiuchus, Scorpio, and
Sagittarius we find wonderful star-clouds, consisting of numberless
stars so distant from us and, therefore, so faint that they do not
appear as distinct points of light except in the greatest telescopes.
It is the combined light from these numberless stars that cannot
be seen separately that produces the impression of stars massed in
clouds of nebulous light and gives to this girdle of the heavens
its name of the Milky Way. In Cygnus, as in a number of other
constellations of both hemispheres, the Milky Way is crossed by dark
rifts and bars and is very complicated in its structure. It is in
Cygnus, also, that one may see with the aid of powerful telescopes
the vast, irregular, luminous nebulæ, that are like great clouds of
fiery mist. These nebulæ are of enormous extent, for they cover space
that could be occupied by hundreds of stars.
[Illustration: SEPTEMBER--CYGNUS]
Cygnus is a constellation that is filled with the wonders and
mysteries of space and that abounds in beautiful objects of varied
kinds. It is a region one never tires of exploring with the
telescope. The principal stars in Cygnus form the well-known Northern
Cross, with the beautiful, white, first-magnitude star Deneb, or
Arided, as it is sometimes called, at the top of the cross, and
Albireo, the orange-and-blue double star at the foot. Albireo,
among all the pairs of contrasting hues, has the distinction of
being considered the finest double star in the heavens for small
telescopes. This star marks the head of The Swan, as well as the foot
of the Northern Cross, and Deneb marks the tail of The Swan. A short
distance to the southeast of Deneb, on the right wing of The Swan,
is a famous little star, 61 Cygni, barely visible to the naked eye
and forming a little triangle with two brighter stars to the east.
This star has the distinction of being the first one to have its
distance from the solar system determined. The famous mathematician
and astronomer Bessel accomplished this difficult feat in the year
1838. Since that day, the distances of many stars have been found
by various methods, but of all these stars only four or five are
known to be nearer to us than 61 Cygni. Its distance is about eight
light-years, so its light takes about eight years to travel the
distance that separates it from the solar system. As a result, we see
it not as it is tonight, but as it was at the time when the light
now entering our eyes first started on its journey eight years ago.
61 Cygni is also a double star, and the combined light of the two
stars gives forth only one-tenth as much light as our own sun. Most
of the brilliant first-magnitude stars give forth many times as much
light as the sun; but among the fainter stars, we find some that
appear faint because they are very distant, and some that are faint
because they are dwarf stars and have little light to give forth. To
the class of nearby, feebly-shining dwarf stars 61 Cygni belongs.
Deneb, on the other hand, is one of the giant stars, and is at an
immeasurably great distance from the solar system.
Just south of Cygnus in the eastern branch of the Milky Way lie
Sagitta, The Arrow, and Aquila, The Eagle. Not far to the northeast
of Aquila is the odd little constellation of Delphinus, The Dolphin,
popularly referred to as Job's Coffin. There will be no difficulty in
finding this small star-group, owing to its peculiar diamond-shaped
configuration. Its five principal stars are of the fourth magnitude.
It is in the constellation of Delphinus that the most distant known
object in the heavens is located. This is the globular star cluster
known only by its catalogue number of N.G.C. 7006. It is estimated to
be at a distance of 220,000 light-years from the earth.
Sagitta, The Arrow, lies midway between Albireo and the brilliant
Altair in Aquila. The point of the arrow is indicated by the star
that is farthest east; and the feather, by the two faint stars to the
west. Like Delphinus, this constellation is very small and contains
no objects of particular interest.
Altair (Flying Eagle) is the brilliant white star of the first
magnitude in Aquila and is attended by two fainter stars, one on
either side, at nearly equal distances from it. These two stars serve
readily to distinguish this star, all three stars being nearly in a
straight line. Altair is one of the nearer stars, its distance from
the earth being about sixteen light-years. It gives forth about ten
times as much light as the sun.
[Illustration: SEPTEMBER--DELPHINUS, AQUILA AND SAGITTA]
We cannot leave the constellation of Aquila without referring to
the wonderful temporary star or nova, known as Nova Aquilæ No. 3
(because it was the third nova to appear in this constellation),
which appeared in the position indicated on the chart upon the
eighth of June, 1918. A few days previous to this date, there was
in this position an extremely faint star, invisible to the naked
eye and in small telescopes. This fact became known from later
examinations of old photographs of this region that had been taken
at the Harvard College Observatory, where the photographing of the
heavens is carried on regularly for the purpose of having a record
of celestial changes and happenings. Clouds prevented the obtaining
of any photographs of this part of the heavens on the four nights
preceding the eighth of June, but on this evening there shone in the
place of the faint telescopic star, a wonderful temporary star, or
nova, which was destined on the next evening to outshine all stars
in the heavens, with the exception of the brightest of all, Sirius,
which it closely rivaled in brilliancy at the height of its outburst.
Within less than a week's time, this faint star in the Milky Way for
some mysterious reason increased in brightness many thousandfold.
Such outbursts have been recorded before, but on rare occasions,
however. No star since the appearance of the nova known as Kepler's
Star, in the year 1604, which at its greatest brilliancy rivaled
Jupiter, shone with such splendor or attracted so much attention as
Nova Aquilæ. In the year 1901, there appeared in the constellation of
Perseus a star known as Nova Persei which at its brightest surpassed
Vega, but its splendor was not as great as that of the wonderful nova
of 1918.
It speaks well for the zeal and interest of amateur astronomers, as
well as for their acquaintance with the stars, that Nova Persei was
discovered by an amateur astronomer, Dr. Anderson, and that among
the deluge of telephone calls and telegrams received at the Harvard
College Observatory on the night of June 8th, announcing independent
discoveries of the "new star," were many from non-professional
astronomers.
Like all stars of this class, Nova Aquilæ No. 3 sank rapidly into
oblivion. In a few weeks it was only a third-magnitude star; a few
weeks more and it was invisible without a telescope. Many wonderful
and interesting changes have been recorded in the appearance of this
star, however, even after it became visible only in the telescope.
Soon after its outburst it appeared to develop a nebulous envelope,
as have other novas before it. It showed in addition many of the
peculiarities of the nebulæ, though the central star remained visible
as before the outburst.
Astronomers are still in doubt as to the cause of these outbursts,
which certainly indicate celestial catastrophies of some form on a
gigantic scale. All novas possess one characteristic in common--that
of appearing exclusively in the Milky Way; and another characteristic
is the development of a nebular envelope after the outburst of
greatest brightness. In some cases temporary stars have been known to
be variable in brightness for years before the great outburst. Such
a star was Nova Aquila, for the examination of photographs of this
region taken some years previous showed variations in its brightness
for a period of thirty years at least.
Up to the beginning of this century only about thirty novas had
been discovered. Since that date, thanks to the vigilance of the
astronomers of today and to the aid of photography, more have been
discovered than in all the preceding centuries. These outbursts
of new stars appear to be not so rare as the earlier astronomers
believed, though great outbursts as brilliant as that of Nova Aquila
are very uncommon.
XI
OCTOBER
The constellations that will be found nearest the meridian in early
October evenings are the circumpolar constellations Cepheus and
Cassiopeia, and in the southern sky, Capricornus and Aquarius.
Cepheus, The King, and Cassiopeia, his Queen, of whom we shall have
more to say later in connection with the constellations of Andromeda
and Perseus, sit facing the north pole of the heavens opposite
Ursa Major, The Great Bear, familiar to us under the name of The
Big Dipper. The foot of Cepheus rests upon the tail of the Little
Bear, and the star farthest north in the diagram is in the left
knee. The head is marked by a small triangle of faint stars, shown
in the diagram. One of these three faint stars--the one farthest
east--known as Delta Cephei, is a very remarkable variable star,
changing periodically in brightness every five and one-third days.
Its name has been given to a large class of variable stars--the
Cepheid variables--that resemble Delta Cephei in being giant suns,
faint only because they are at very great distances from the earth,
and varying in brightness with the greatest regularity in periods
that range from a few hours to several weeks. It has been found that
the longer the period of light change the greater is the star in
size and brightness. The Cepheids of longest period are 10,000 times
more brilliant than our own sun. Cepheus contains no very bright or
conspicuous stars. Alpha Cephei, the brightest star in the group,
marks The King's right shoulder. It is the star farthest to the west
in the diagram, and is only a third-magnitude star.
[Illustration: OCTOBER--CASSIOPEIA AND CEPHEUS]
Cassiopeia is a constellation with which every one in the northern
hemisphere should be familiar, owing to its very distinctive W-shape
and its far northern position, which brings it conspicuously into
view throughout the clear fall and winter evenings. Cassiopeia is
pictured in all star atlases that show the mythological figures,
with her face toward the north pole. The stars in the W outline the
body. Alpha, the star farthest south in the diagram marks the breast
of Cassiopeia. Her head and uplifted hands are represented by faint
stars south of Alpha. This star is occasionally referred to by its
Arabic name of Schedir. Beta, the leader of all the stars in the W in
their daily westward motion, is also known by an Arabic name, Caph.
In the constellation of Cassiopeia there appeared in the year 1572
A.D., a wonderful temporary star which suddenly, within a few days'
time, became as brilliant as the planet Venus and was clearly visible
in broad daylight. This star is often referred to as Tycho's Star,
because it was observed, and its position very accurately determined,
by Tycho Brahe, one of the most famous of the old astronomers. This
star remained visible to every one for about sixteen months, but it
finally faded completely from view, and it is believed that a faint,
nebulous red star, visible only in the telescope and close to the
position recorded by Tycho, represents the smoldering embers of the
star that once struck terror to the hearts of the superstitious and
ignorant among all the nations of Europe, who took it to be a sign
that the end of the world was at hand.
Both Cassiopeia and Cepheus lie in the path of the Milky Way, which
reaches its farthest northern point in Cassiopeia and passes from
Cepheus in a southerly direction into the constellation of Cygnus.
[Illustration: OCTOBER--AQUARIUS AND CAPRICORNUS]
Turning now to southern skies, we find on and to the west of the
meridian at this time the rather inconspicuous zodiacal constellation
of Capricornus, The Goat. It contains no stars of great brightness
and is chiefly remarkable for the fact that it contains one of the
few double stars that can be seen without the aid of a telescope.
The least distance in the heavens that the unaided human eye can
separate is about four minutes of arc. The star Alpha in Capricornus
is made up of two stars separated by a distance of six minutes
of arc, so that any one can readily see that it consists of two
stars very close together. This star, Alpha, will be found in the
extreme western part of the constellation, and can best be located
in conjunction with the star Beta, which is slightly brighter and
lies but a short distance almost due south of Alpha, the two stars
standing somewhat alone in this part of the heavens.