star which is named Alcor (signification uncertain). The Arabs are
said to have called these two stars the “Horse and his Rider,” and
to have regarded it as a test of good vision to be able to see them
both. It is certainly not a severe test at present. Mizar itself
is telescopically double, presenting a beautiful sight in a small
telescope, the distance asunder being about 14″. The smaller star is
like an emerald in hue, and the color is usually remarked at once by
the beginner in telescopic observation. The larger star is one of
those strange objects called “spectroscopic binaries”--two suns locked
in the embrace of gravitation and spinning round a centre so near to
each other that to anything less penetrating than the magic eye of the
spectroscope they appear as a single body.
Merak and Dubhe are the celebrated “Pointers,” so called because a line
drawn from the former to the latter, and continued toward the pole,
passes close to Polaris, the Pole-star, of which we shall presently
speak. The distance between these stars is about five degrees, so that
they serve as a rough measuring-stick for estimating distances in the
sky. Immediately west of the meridian will be seen a curving row of
stars which indicate the head of the Bear. Three of his feet, or claws,
are represented by as many pairs of stars between the Great Dipper and
the Sickle of Leo, one of the pairs being east of the meridian, one
west of it, and one nearly upon it. Below the outer end of the handle
of the Dipper, in the direction of Denebola, a fairly bright star, Cor
Caroli, which English loyalty named for the heart of the unfortunate
King Charles I., shines on the collar of one of the “Hunting Dogs,”
Canes Venatici, which Boötes is represented as holding in a leash as
he chases Ursa Major round the pole. This, too, is a beautiful double,
the contrasted colors of whose widely separated stars are finely shown
by a small telescope.
Now let the eye run along the curve of the Dipper’s handle, beginning
at the bowl, and then, springing on, continue the same curve eastward;
it will encounter, at a distance about equal to the whole length of the
Dipper, a very great and brilliant star--Arcturus, brighter than Spica
and Regulus, and usually, when not very far risen from the horizon, of
a distinctly reddish hue. It is the chief star of Boötes, the “Driver,”
the “Vociferator,” the “Herdsman,” or the “Bear-watcher,” as it has
been variously rendered. We shall have more to say about Boötes in
another chapter, but Arcturus is a star so splendid and famous that
it cannot be passed in silence the first time the beginner catches
sight of it. There is a standing dispute concerning the relative rank
in brightness of Arcturus among the leading stars of the northern
hemisphere. Its principal rivals are Vega in the Lyre, and Capella in
Auriga. But all three differ in color, and that makes it more difficult
to decide upon their relative brilliance, since different eyes vary in
their sensitiveness to color. The Harvard Photometric _Durchmusterung_
gives Vega the first and Arcturus the third rank among these three;
but many eyes recognize rather a pre-eminence of Arcturus. My own
impression has usually been that Arcturus looms larger than either Vega
or Capella, but that Vega is the most penetratingly brilliant. It is
very curious to notice the effect of the colors of these stars. The
sharp blue ray in the light of Vega gives it a diamond-like quality
which is lacking in Capella, whose light is white with just a suspicion
of amber. Arcturus is a very pale topaz when high in the sky, and a
ruddy yellow, sometimes flaming red, when near the horizon. It is a
thrilling recollection of the writer’s early boyhood that he felt an
undefined fear of Arcturus when seen rising ominously red and flashing
through the leafless boughs of an apple orchard in the late evenings of
February. All the ancients feared Arcturus for its supposed influence
in producing storms and bad harvests.
Arcturus is a sun of enormous magnitude, estimated all the way from one
to six thousand times as great in luminosity as our sun. It is also
travelling with great rapidity, its speed, according to some estimates,
amounting to two or three hundred miles per second; but most of this
is cross-motion with reference to us, its general direction being
toward the south-southwest. If it is travelling three hundred miles per
second, it would traverse the space between the sun and the nearest
star, Alpha Centauri, in about three thousand years. We shall touch on
Arcturus again when dealing with Boötes in the next chapter.
Disregarding for the present the exquisite circlet of Corona Borealis,
the “Northern Crown,” and the quadrilateral figure in Hercules, seen
northeast of Arcturus, we turn to the great dragon, Draco, whose
diamond-shaped head may be seen far over in the northeast above
sparkling Vega, which is just on the horizon. As a reference to the
charts of the circumpolar stars at the end of the book will show,
Draco is a remarkably crooked constellation, its line of stars winding
round between the “Little Dipper” in Ursa Minor, which has Polaris at
the end of its handle, and the “Great Dipper” of Ursa Major. Its most
interesting, though not now its brightest, star is Alpha, or _Thuban_,
Arabic for “dragon.” It lies between the end of the handle of the Great
Dipper and the bowl of the small one. About forty-six hundred years
ago Alpha Draconis was the Pole-star, and is believed to have shone
down the long tube-like passage in the great pyramid of Cheops into
the watching eyes of the priestly astronomers, assembled to view it
in the mysterious chamber hollowed out of the solid rock deep under
the foundations of the mighty pile. They thus had a telescope more
than three hundred feet long as immovable as the solid earth, but,
alas for their calculations, the star itself shifted its position,
and their gigantic observing tube became useless until modern science
inferred from its position the date of their building. How imposing
to the imagination this association between a particular star and the
mightiest structure made by human hands on the earth! Two centuries
ago Thuban was more than twice as bright as it is now, and when the
Egyptian priests sedulously observed it from their gloomy cavern, more
than a thousand years before the magic-working days of Moses, it may
have been brighter still.
Gamma (γ), or Eltanin (the “Dragon”), in the triangular head, is now
the brightest star in the constellation, and it, too, has a history.
Lockyer and others have identified it as the orientation star of
Rameses’ great temple at Karnak, and of the temples of Hathor and Mut
at Dendera and Thebes. There is something magnificent in this thought
of the ancient temple-builders--to square their work by the stars, and
to construct long rows of sphinxes and majestic columns to conduct a
ray from the sky to the eye of the god in his dark and hidden chamber,
where no impious foot dared follow.
When you are tired of tracing the windings of the Dragon, turn to Ursa
Minor and Polaris. The “Little Bear,” it has been remarked, has an even
more preposterous tail than his greater brother. Polaris is at the end
of the tail, or the end of the handle of the Little Dipper, and the
bowl of the latter is on the bear’s flank.
If one knows nothing else of uranography, one should at least know
Polaris, the “North Star.” To recognize that star is to be able to
orient yourself wherever you may be in the northern hemisphere. A whole
volume could be written on its connection with human affairs. For at
least two thousand years it has been the cynosure of sailors, and of
wanderers by land as well. You cannot be lost if you have Polaris to
guide you. The magnetic compass varies and misleads, the sun and
the moon change their places, all the other stars circle through the
heavens, but Polaris is always there, shining over the pole of the
earth, the image of steadfastness. Only the slow Precession of the
Equinoxes affects it. At the present time it is within one degree and
a quarter of the true pole of the heavens, and it is drawing nearer
that point, so that in two hundred years it will be less than half a
degree from it--less than the apparent diameter of the moon. The little
circle that it daily describes in the sky may be disregarded, for it
is hardly noticeable except with instruments; but it is easy to fix
the star’s position with considerable accuracy by simple observation.
Note that the Great Dipper and the “W”-shaped figure in Cassiopeia are
on opposite sides of the pole. When one is above, the other is below;
when one is on the east, the other is on the west. Draw an imaginary
line from the star Mizar in the Great Dipper to the star Delta (δ) in
Cassiopeia and it will pass almost directly through the pole. Polaris
is on that line, a degree and a quarter from the pole in the direction
of Delta Cassiopeiæ. If the observation is made when Delta is above
the pole and Mizar below it, Polaris will be on the meridian, or north
and south line, a degree and a quarter above the pole; when Delta is
west of the pole and Mizar east of it, Polaris will be a degree and a
quarter west of the meridian; when Delta is below the pole and Mizar
above it, Polaris will be on the meridian a degree and a quarter below
the pole; and, finally, when Delta is east of the pole and Mizar west
of it, Polaris will be a degree and a quarter east of the meridian. The
intermediate positions you can easily deduce for yourself.
But Polaris will not continue to be the unerring guide to the north
that it now is. The Precession of the Equinoxes is carrying the
pole progressively westward in right ascension, so that Polaris
will eventually be left far behind. But the motion of the pole is
in a circle about twenty-three and a half degrees in radius, and it
requires about 25,800 years to complete a revolution round this circle.
Consequently, at the end of that period, Polaris will have come back
to reign again as the North Star for many centuries. In the interim
other stars will have occupied its place. About 11,500 years from now
the brilliant Vega, or Alpha Lyræ, will be the North Star, and in
about 21,000 years Alpha Draconis (Thuban) will once more shine down
the great northward-pointing passage in the pyramid of Cheops, if that
pyramid shall still exist.
Polaris, unlike some of the others stars that we have been looking
at, is running away into space instead of approaching us, at a speed
which has been estimated at about 1,380,000 miles per day. Its present
distance is not less than 200,000,000,000,000 miles. It has an
invisible companion with which it circles in an orbit of a few million
miles diameter in a period of about four days.
Polaris is also a celebrated visual double. With a telescope of two
or three inches aperture you can see close by its flaming rays a
minute blue star, a delicately beautiful sight. In the older days of
telescopes, before they had attained the perfection which improvements
in glass-making and lens-shaping have rendered possible, this little
companion star of Polaris was a universal test of excellence. Its
prestige was historical. The amateur owner of a telescope who could
see that star clearly felt a joy that he could hardly express. The old
makers of object-glasses, by rule of thumb, always tried them on the
companion of the Polestar as a standard test for small apertures. The
small star is of the ninth magnitude, and situated about 18″.6 from its
primary.
The stars Beta (β), or Kochab (the “Star”), and Gamma (γ), in Ursa
Minor, are called the Wardens, or Guards, of the Pole. In low northern
latitudes, where these stars sweep the horizon at their lower
culmination, Shakespeare’s description in _Othello_ would be literally
true during a great storm at sea:
“The wind-shak’d surge, with high and monstrous mane,
Seems to cast water on the burning Bear
And quench the guards of th’ ever-fixed pole.”
The constellations Cepheus, Cassiopeia, and Perseus, now low in the
northwest and north, we leave for description to another chapter.
II
THE EVENING SKY AT THE SUMMER SOLSTICE
At 10 o’clock P.M. on the 21st of June, the longest day of the
northern hemisphere, the aspect of the sky is that shown in Chart II,
accompanying this chapter. The same chart will answer for 11 P.M. on
the 5th or 6th of June; 9 P.M. on the 7th of July, and 8 P.M. on the
22d or 23d of July. In fact, for any of the hours mentioned the date
may be shifted several days forward or backward without seriously
affecting the comparison of the chart with the sky, and the same may be
said of each of the other circular charts. The stars simply rise about
four minutes earlier each evening, and four minutes of time correspond
to one degree of space measured on the face of the sky. So the whole
sky shifts about one degree westward every twenty-four hours.
For the observation of the heavens at the epoch of the Summer Solstice,
observers who are situated at least as far south as 40° north latitude
have an advantage over those whose place on the earth is much farther
north, because in the more northern regions sunset occurs later, and
in England and Northern Europe the day, at this time, may exceed
sixteen hours in length, while twilight is perceptible throughout
the night. This interferes with the brilliancy of the stars.
[Illustration: CHART II--THE SUMMER EVENING SKY]
At no other season do the heavenly bodies seem so intimately associated
with the earth as in summer. All nature is now attuned, and the stars
glow softly in the tepid atmosphere, stirred by faint breezes, like
veritable flowers of the sky. The firmament becomes a vast garden lit
with beautiful lamps, which seem to have been placed there to dimly
illuminate nocturnal wanderers in the transparent gloom beneath. Their
beauty is as refreshing as the cooling breath of night itself. A mystic
influence steals from them over the earth.
“If a man would be alone,” says Emerson, “let him look at the stars.”
Yet he cannot be alone with them; they are too friendly; they speak too
plainly a universal language, which, though he cannot translate it,
he _feels_ in every fibre. There is nothing more absolutely common to
all men than the influence of the stars. No one ever gazed up at them
without feeling a change come over his spirit. Truly, “they separate
between him and what he touches.” They free him from the bondage of
time and space. There is no trouble that they cannot assuage. And there
is no time like the summer for becoming intimate with them. One who has
been touched by the magic of their love could lie all the night long on
a bed of pine-needles and fill his soul with their beauty. The march of
red Antares and his glittering retinue across the meridian while the
earth sleeps in solstitial calm--who can describe that pageant?
Antares is _the_ summer star, and with it and the Scorpion we will
begin. Not so bright as Arcturus or Vega, which are now high aloft, it
has a charm peculiar to itself, arising partly from its fervid color,
partly from its surroundings, and partly from its position, not too
high above the southern horizon, which renders observation of the star
comparatively easy. The color is so distinctive that one might think
that he could recognize Antares chromatically if it were suddenly
transported to some other region of the sky and placed amid a strange
environment. Sometimes a flash of its fiery rays, striking sidewise
into the eye as one is looking elsewhere, startles the observer like a
red meteor. It is well named Antares--“Anti-Mars.” With the telescope
the wonder of color is increased, for close by the great star the
glass reveals a smaller one of a _vivid green_, an all but incredible
combination of complementarily tinted suns. And these suns are
undoubtedly actually linked together into a system, so that, if there
are planets revolving around both or either, the inhabitants of those
planets may behold the spectacle of two suns, one crimson and the other
emerald! The large star is of the first magnitude, and the small one of
the seventh; angular distance 3″.7.
The companion of Antares is historically associated with the most
interesting of American astronomers, a man whose life was a romance,
Gen. O. M. Mitchel. When his long-cherished design of setting up a
great telescope in America was at last fulfilled, at Cincinnati, in
1845, one of his first achievements was the discovery, to the surprise
of the astronomers of Europe, of the green star hiding in the rays of
Antares. At times it has been seen emerging from behind the moon, after
an occultation, ahead of its red comrade.
With a parallax of 0″.02, Newcomb estimated the luminosity of Antares
at nine hundred times that of our sun, and yet the spectroscope
indicates that it is a dying sun, fast approaching extinction. In its
younger days it may have been an orb of prodigious splendor.
The constellation Scorpio, of which Antares is the leader, is one of
the best marked in the sky. The two small stars Sigma (σ) and Tau (τ),
standing like attendants on either side of Antares, lend a singular
aspect to the central part of the constellation. Antares is usually
represented as the heart of the imaginary scorpion. Below Tau a curving
row of stars dips to the southern horizon, and then rises, farther
eastward, terminating with a conspicuous pair in the uplifted sting.
West of Antares a nearly vertical row represents the head. Of the
stars in this row, Beta (β) is interesting as a fine and easily seen
double, the distance being about 13″. A higher magnifying power shows
that the larger star has another faint companion, distant only 0″.7. Nu
(ν) is also telescopically interesting, for it consists of two pairs
of stars. Observe in Chart VII the strange way in which the outlines
of the constellation have been swung into loops in order to include
certain stars in Scorpio, recalling the crooked boundary between
Switzerland and Italy, by which each reserves particular peaks of the
Alps for itself.
East of Scorpio, where the Milky Way, falling in flakes and sheets of
silvery splendor upon the southeastern horizon, spreads abroad like an
overflowing river, lies Sagittarius, the “Archer,” often represented
in the old pictorial charts as a centaur. The stars Lambda (λ), Delta
(δ), and Epsilon (ε) form the bent bow. But modern eyes recognize more
easily a dipper, formed by the stars Zeta (ζ), Tau (τ), Sigma (σ),
Phi (φ), Lambda (λ), and Mu (μ). But the star-clusters in Sagittarius
are more interesting than the separate stars. A little southwest of
Mu is the famous cluster 8 M., of which Barnard has made a photograph
that is amazing beyond all description. Other clusters are all about
in this part of the sky. A good opera-glass or field-glass is almost
indispensable for one who would enjoy the glory of this wondrous
region. Its riches are almost oppressive in their lavish abundance.
Here one can have handfuls of stars for the picking up, like sands of
gold from the bed of Pactolus. As the glittering incrustations that
cover the roofs and walls of the Mammoth Cave are often compared to
the starry heavens, so, reversing the image, Sagittarius is like a
stupendous cavern of space all ablaze and aglitter with millions of
sparkling gems.
Above Scorpio and Sagittarius are the intertwined constellations
of Ophiuchus and Serpens. He who may wish to disentangle them is
referred to _Astronomy with the Naked Eye_. But the outlines can be
traced in Chart VII. The head of Serpens, like those of Hydra and
Draco, is plainly marked by a striking group of stars, in this case
resembling the figure called a “quincunx.” From this point just under
the “Northern Crown,” the serpent’s stars wind downward in beautiful
pairs and groups, crossing the meridian above Scorpio, and rising again
in the eastern part of the sky, above the little constellation of
Sobieski’s Shield, until they meet the borders of Aquila. Ophiuchus,
with his head high up toward Hercules, where it is marked by the
brightest star in that part of the sky, Alpha Ophiuchi, or Ras Alhague,
the “Head of the Serpent Charmer,” stands with legs braced wide apart,
grasping the serpent at the points marked by the stars Delta (δ) and
Epsilon (ε), and Tau (τ) and Nu (ν). It is Esculapius with his Serpent,
said the Greeks; it is St. Paul and the Viper of Melita, or Moses and
the Brazen Serpent, we don’t know which, said the churchmen. I am
not aware that in England they have ever been tempted to call it St.
George and the Dragon. Politics and national pride have not meddled
much with the stars, although there was once an attempt to fix the name
of Napoleon upon Orion. Ras Alhague is described by R. H. Allen as
sapphire in hue, while Alpha Serpentis is yellowish. The star Lambda
(λ) in Ophiuchus, also called Marfik, the “Elbow,” is a beautiful
binary, period 235 years, distance apart 1″.2. The smaller star is
smalt blue, a splendid telescopic object.
But, as in the case of Sagittarius, the greater wonders here are in the
form of star-clusters, and particularly nebulæ. Just above Antares,
in one of the feet of Ophiuchus, is a small star, Rho (to find which
the reader must consult a large star atlas, like Klein’s), around
which Barnard has discovered, by photography, a truly marvellous
nebula, a nebula which appears _to obscure the stars_ like a cloud of
cosmic dust. Great black lanes extend from and around it, and even the
luminous parts of the nebula seem to absorb the light of the stars
behind, diminishing their brightness a whole magnitude or more where
they are veiled by it. This entire region of sky is most strange to the
photographic eye. An outlier of the nebula just mentioned surrounds the
star Nu (ν) in Scorpio, and its veiling effect upon the stars is even
more evident. There is a similar appearance around the star Theta (θ)
Ophiuchi, not far away. The sense of some appalling mystery in this
part of the firmament is heightened by what Barnard says of a thing
which has reappeared again and again on his photographs during the past
fifteen years, at a point which he describes as lying very closely to
R. A. xviii hours, 25 m., 31 s.; Decl. S. 26°, 9′ (near the star Lambda
(λ) in Sagittarius).
“It is a small, black hole in the sky. It is round and sharply defined.
Its measured diameter on the negative is 2′.6. On account of its
sharpness and smallness and its isolation, this is perhaps the most
remarkable of all the black holes with which I am acquainted. It lies
in an ordinary part of the Milky Way, and is not due to the presence or
absence of stars, but seems really to be a marking on the sky itself”
(_Astrophysical Journal_, January, 1910).
These things really transcend explanation (see _Curiosities of the
Sky_).
Above Ophiuchus and his Serpent, almost exactly overhead in the
latitude of 40° N., we see the quadrilateral figure marked out by four
of the principal stars of the constellation Hercules. The head of
Draco, described in Chapter I, is beyond it toward the north-northeast.
Hercules stands feet upward in the sky, his head, indicated by the
star Alpha, or Ras Algethi, the “Kneeler’s Head,” being situated a few
degrees west-northwest of Ras Alhague. Thus the two giants have their
heads together. But while the occupation of Ophiuchus is plain, nobody,
not even in ancient times, when the constellation received its name,
has ever been able to say what Hercules is laboring at. When he was on
the earth everybody followed his deeds and understood, if they could
not emulate, them. He was as comprehensible as a modern pugilist. Now,
however, that he has been translated to the stars, his labors are of
a more mysterious nature, and, judging from his attitude, he finds
them harder than any he undertook for the benefit of mankind here
below. One is tempted to think that the powers he offended, when he
boldly entered the land of shades and snatched the wife of his friend,
King Admetus, from the hand of Death himself, are now taking an ample
vengeance.