AN INTRODUCTION TO THE STARS
"_He who knows what sweets and virtues are in the ground, the waters--the
planets, the heavens, and how to come at these enchantments, is the rich
and royal man._"
--_Emerson_.
THE dome of the heavens with its constellations of stars turns westward
at the rate of about 15 degrees an hour.
Thus the stars, in unchanging order, rise majestically above the horizon
in the east, wend their way across the great expanse of sky above our
heads, and disappear below the horizon in the west. It is only necessary
to note the position of a particularly bright star or a conspicuous
constellation lying near the horizon and then return after several hours
have elapsed and again note its position in the sky to prove this
general movement toward the west. This is an interesting experiment for
it is often a surprise to people to hear that the stars of the heaven
are constantly shifting their position throughout the hours.
Each star has an individual pathway which describes an arc across the
heavens, the exception to this being the circum polar stars which
describe complete circles around a point north of the zenith.
The center indicated by the curved pathways of the stars is called the
Pole of the Heavens, and in the northern hemisphere this important
location is marked by the North Star. The North Star, also called
_Polaris_ or the Pole Star, lies almost directly above the north
pole of the earth, and is located in the sky by the "pointers" on the
bowl of the Big Dipper.
[Figure 02]
Since we cannot realize the whirling of the earth on its axis which
causes the heavenly bodies to appear to pass in the opposite direction,
it is the same to us as if the axis of the earth continued upward to
Polaris, thus causing this star to seem to stand still, while all the
other stars in the course of twenty-four hours seem to whirl in fixed
orbits around it.
"The earth in circling round the moving sun,
Seems to give motion to the nearer stars,
Bending the tracks they trace across the sky."
This remarkable performance may be photographed on a clear, moonless
night if a camera is properly focused on the North Star and left exposed
in that position for two or three hours. The photograph thus obtained
will consist of a series of circular trails around the central star.
These are produced by the stars moving slowly over the plate in
consequence of their changing positions,--just as if the stars instead
of our own little world had really moved. This is what the ancient
peoples believed and in the words of Aratus
"the axis shifts not a whit, but unchanging is forever fixed, and in the
midst of it holds the earth in equipoise, and wheels the heavens itself
around."
Since the stars were always in the same order with reference to one
another, it was thought that perhaps these luminaries were the heads of
golden nails which made the heavenly dome secure. Thus through their
apparent immovability, they acquired the name of "fixed" stars, although
this fixity has long since been disproved.
The stars nearest to the North Star complete their circles above the
horizon and are called circumpolar stars. The Big Dipper, the Little
Dipper, Draco and the "W" of Cassiopeia are star groups which do
this for an observer in the north temperate latitudes. If watched
throughout the night any one of these star groups may be seen to
complete half of its circle around the North Star, although the other
half of the journey would be invisible on account of the daylight.
Although the circumpolar stars may be seen to complete their pathways
above the horizon, the pathways of all the other stars are completed on
the other side of the earth,--the greater the distance from the North
Star, the larger their arcs above the horizon, until the distance of 90
degrees is reached. This greatest curve is shown by the stars which rise
almost directly in the east. The stars which rise south of east have
only a small portion of their pathways visible.
It would seem that since the stars move as a complete unit, the aspect
of the star dome would appear the same at the same hour of the night
throughout the year. But this is known not to be the case for in
consequence of the earth's motion around the sun, or the apparent
advance of the sun among the stars, the same position of the stars
re-occurs four minutes earlier each day, and the star groups appear a
little farther west at a given hour each evening. They appear at the
same time only after the lapse of a year. This is the reason that the
dates and hours for the appearance of the different stars are given in
the star maps. Since four minutes a day total up to two hours a month, a
star seen to rise at ten o'clock in one month will be seen to rise at
eight o'clock the next month, and at six o'clock the following month,
and so on through the daylight at the rate of two hours a month, until
it has again worked back to a place in the darkness of the evening sky.
The number of the stars is beyond determination, but those visible to
the unaided eye amount to only a few thousands.
Many stars on the border-line of invisibility send us flickering glints
of light although seldom can we clearly see more than two thousand at
one time and usually many of these are blotted out by the thick veil of
atmosphere which surrounds the earth.
Among the exceptionally bright stars which may be seen from the northern
hemisphere are:
Arcturus (in Boötes) Regulus (in Leo)
Aldebaran (in Taurus) Vega (in Lyra)
Altair (in Aquila) Antares (in Scorpio)
Betelgeuse (in Orion) Rigel (in Orion)
Capella (in Auriga) Sirius (in Canis Major)
Procyon (in Canis Minor) Spica (in Virgo)
Deneb (in Cygnus) Formalhaut (in Piscis Australis)
Yet even these cannot be seen at the same time but must be viewed from
different parts of the earth's journey around the sun.
These brightest stars, which are called first magnitude stars, should be
among one's first star acquaintances, for they serve conveniently as
guides to locate the other stars, which are also classified according to
magnitudes. The second, third, fourth and lesser magnitudes are each
progressively two and a half times lower in the scale of brightness. The
smallest stars discernible to the unaided eye of ordinary vision are
stars of the fifth magnitude, although a sharp eye can discern those of
the sixth and even of the seventh magnitude. All below this are
telescopic stars. With a 60-inch reflector 219,000,000 stars are
visible. The Mount Wilson 101-inch telescope brings the number up to
319,000,000. Stars are most dense in the region of the heavens called
the Milky Way. Sir William Herschel observed 116,000 go past the field
of his telescope in a quarter of an hour while directed at the densest
part of the Milky Way.
This vast collection of stars differ not only in brightness but also in
color.
The colors of the stars are brought out most vividly in the telescope if
the observer knows just where to look for those which are the most
pronounced. Some of the large stars are characterized by the most
exquisite coloring,--which is sometimes further enhanced, as a glass
will reveal, by a charming companion of a flamboyant or a delicate hue.
Some of these "companions" are green, blue, orange, purple, gray, maroon
and other colors, but such gayety is the exception rather than the rule.
About three-fourths of the stars are white or bluish-white and nearly
one-fourth of them are varying shades of yellow. The star Arcturus is of
the deepest shade of yellow while the star Spica is so exceedingly white
that poets and writers from the earliest times have spoken of the
"purity" of its rays.
Although every star visible to the unaided eye may be identified by a
Greek letter or a number, most of the brightest stars have individual
names.
These individual names were given by the Arabian astronomers who
nurtured astronomy through the Dark Ages when this science was almost
forgotten by the rest of the world. These odd names have a certain
appeal and many of them possess rippling musical qualities which add to
the plain word as twinkles add to the star. It is a pleasure to say
'Capella,' or 'Antares,' when we see the gleam of the "Shepherd's Star,"
or the glow on the "Heart of the Scorpion"; or to call such jewels as
shine on "Orion's Belt," 'Mintaka,' 'Alnilam' and 'Alnitak.' After the
introduction one naturally takes a particular interest in 'Capella,' or
'Antares,' or 'Mintaka,' or 'Alnilam,' and continues to refer to it
familiarly by name.
Each star not only attains a certain charm and individuality by having
its own particular name, number, magnitude, color and pathway, but
it also forms a part of a highly interesting group called a
constellation.
On a clear night points of starlight seem to fairly fill the sky, yet it
will be found, on careful examination, that the brightest of them often
seem to be assembled together in a very picturesque manner, forming the
outlines of figures such as the Dippers, the Crown, the Cross, the
Sickle or the Lyre. Since these designs unfailingly deck the heaven's
dome at the same place, hour and season each year, there is not the
hopeless confusion among the stars that the novice might think from his
occasional glances at the sky.
These star groups, or constellations, were probably first noted and
named in Chaldea where the ancient shepherds amused themselves by
tracing their heroes among the stars. One can well imagine the hold that
these dream-pictures would have on a lonely shepherd as he wandered
about the solitudes of the hills and gazed through the quietness of the
night at the distant stars. For long ages these stories were told by one
shepherd to another and so vivid were their fancies and so keenly were
they enjoyed that they made an indelible impress upon the folk-lore of
other nations and in this manner have been carried down to the present
day.
The stars are self-luminous, like our sun,--indeed, the stars are
distant suns, and the sun is a nearby star.
With the exception of the star or sun around which the earth and the
other planets of our solar system whirl, all the other suns are so
immensely remote from the earth that their huge diameters dwindle to a
mere twinkle of light. The diameters of some of the stars have been
measured and have been found to vary from a few thousand miles to many
million miles. Our sun, a most medium sized star, has also been measured
and has a diameter of 866,000 miles; this diameter, as seen from
any other system of planets, would also dwindle to a twinkle, and our
great sun would thus be lost among the other stars.
Throughout the sky are young stars, adult stars, and stars whose light
has almost flickered out, for stars, we find, even as all other things
in Nature, have a limited span of life. This life may last for untold
ages but as surely as stars are formed, so do they die.
The nucleus of a star is formed by gas under high pressure. This gas is
gathered together by the force of gravity and gradually condensed into a
glowing ball. In contracting the stars at first rise in temperature but
when too advanced condensation retards this contraction, then the star
gradually cools.
Recent studies have revealed the fact that stars when young are huge and
red. This early stage is called the giant stage. Antares, Betelgeuse,
Arcturus and Aldebaran are examples of stars at the beginning of their
careers. The giant red stars are gaseous throughout and of enormous
volume--Antares, the youngest and by far the largest of the four named
above, being 400,000,000 miles in diameter. The bluish stars are the
hottest stars; a red tinge indicates comparative coolness whether the
star is young or old. The blue stars are in the prime of life, intensely
hot and brilliant, and glow with a temperature of perhaps 10,000 degrees
at their luminous surfaces. With a gradual rise and fall of temperature,
stars burn, even as earthly flames, through a continuous series of
colors,--generally speaking, red, yellow, blue, yellow, red,--all of
which bear a special meaning to an astronomer. The yellow stars, like
our sun, are middle-aged; the dwarf red stars, old, like a dying ember.
After a star has expended its heat, if it does not in the meantime meet
with some accident, it becomes a darkened, lifeless and cold-surfaced
globe.
[Figure 03: AN IRREGULAR NEBULA IN SCUTUM SOBIESKI.
Photograph by Mount Wilson Observatory through 60-inch reflecting
telescope.]
The material believed to condense into great hot stars is scattered
about in various sections of the sky. This material has somewhat the
appearance of a summer-day cloud or an illuminated daub of paint,
occasionally as shapeless as a pinch of cotton; however, these objects,
called nebulæ, have, as a rule, a definite form, the most common being
the 'spiral,' the 'ring' and the 'planetary,' these terms also being the
descriptive names of such nebulæ. But most of the nebulæ are not for
ordinary folks to see for they lie at such vast distances that they are
only visible in a large telescope. Sometimes stars are disclosed
enmeshed in nebulous folds or again the nebula is seemingly sprinkled
with the gold of stars, and there is one object of this kind that every
amateur may locate. This is the Great Nebula of Orion which stretches
over the whole of the huge constellation of Orion but is concentrated at
the star at the center of the Sword which swings from the Giant's Belt.
"I never gazed upon it but I dreamt
Of some vast charm concluded in that star
To make fame nothing."
--_Tennyson_.
The Nebula of Orion may be seen in the south in the wintertime with a
comparatively small telescope. With a large telescope it is one of the
most beautiful and awe-inspiring sights in all the sky.
One theory of the life cycle of a star has it born "of nebulous vapor
and dead as a tiny, shrunken old sun" and thus the order of evolution
would be from nebulæ to extinct stars, but some astronomers believe
that stars may change back to nebulæ, "thus forming a universe having
no beginning and no end".
The earth travels in a long journey around the sun. This was surmised by
Copernicus in 1530 and proved by Kepler and Galileo about 1610.
Before this the earth was supposed to be the center about which the
universe moved.
[Figure 04]
The star scenes along this tremendous journey, which covers 576,000,000
miles and requires a year to complete, vary with the seasons of the
year--yet year after year as we retrace the same path, the same familiar
stars shine in the same familiar groups, each appearing in its set
position in the east and at the same time each season.
Viewed through the window of the earth's cold and icy atmosphere, the
stars seen during the winter part of the journey seem to scintillate
with particular brilliancy. Since we are then passing by the most
colorful stars and the most spectacular star groups the gorgeousness of
these scenes is unequaled. During the summer the stars are more demure
and tranquil in their light but their soft fires gleam with the gold of
romance which the ancient people cast about them in journeys of the
past. After once recognizing a few of these constellations or beholding
through a telescope the glories of a double star or the face of a
distant world, one will never again fail through indifference to raise
his eyes to the heavens. There is one thing certain--if all the wondrous
phenomena of visible stars could be seen on but one of the nights of our
long ride about the sun, the civilized world would spend its last cent
on glasses and sit up until dawn to feast its eyes on the sublimity of
the spectacle.