FROM GEMINI TO LEO AND ROUND ABOUT
"If thou wouldst gaze on starry Charioteer,
And hast heard legends of the wondrous Goat,
Vast looming shalt thou find on the Twins' left,
His form bowed forward."--POSTE'S ARATUS.
[Illustration: MAP NO. 4.]
The zodiacal constellations of Gemini, Cancer, and Leo, together with
their neighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices,
will furnish an abundance of occupation for our second night at the
telescope. We shall begin, using our three-inch glass, with alpha, the
chief star of Gemini (map No. 4). This is ordinarily known as Castor.
Even an inexperienced eye perceives at once that it is not as bright as
its neighbor Pollux, beta. Whether this fact is to be regarded as
indicating that Castor was brighter than Pollux in 1603, when Bayer
attached their Greek letters, is still an unsettled question. Castor may
or may not be a variable, but it is, at any rate, one of the most
beautiful double stars in the heavens. A power of one hundred is amply
sufficient to separate its components, whose magnitudes are about two
and three, the distance between them being 6", p. 226 deg.. A slight yet
distinct tinge of green, recalling that of the Orion nebula, gives a
peculiar appearance to this couple. Green is one of the rarest colors
among the stars. Castor belongs to the same general spectroscopic type
in which Sirius is found, but its lines of hydrogen are broader than
those seen in the spectrum of the Dog Star. There is reason for
thinking that it may be surrounded with a more extensive atmosphere of
that gaseous metal called hydrogen than any other bright star possesses.
There seems to be no doubt that the components of Castor are in
revolution around their common center of gravity, although the period is
uncertain, varying in different estimates all the way from two hundred
and fifty to one thousand years; the longer estimate is probably not far
from the truth. There is a tenth-magnitude star, distance 73", p. 164 deg.,
which may belong to the same system.
From Castor let us turn to Pollux, at the same time exchanging our
three-inch telescope for the four-inch, or, still better, the five-inch.
Pollux has five faint companions, of which we may expect to see three,
as follows: Tenth magnitude, distance 175", p. 70 deg.; nine and a half
magnitude, distance 206", p. 90 deg., and ninth magnitude, distance 229", p.
75 deg.. Burnham has seen a star of thirteen and a half magnitude, distance
43", p. 275 deg., and has divided the tenth-magnitude star into two
components, only 1.4" apart, the smaller being of the thirteenth
magnitude, and situated at the angle 128 deg.. A calculation based on Dr.
Elkin's parallax of 0.068" for Pollux shows that that star may be a
hundredfold more luminous than the sun, while its nearest companion may
be a body smaller than our planet Jupiter, but shining, of course, by
its own light. Its distance from Pollux, however, exceeds that of
Jupiter from the sun in the ratio of about one hundred and thirty to
one.
In the double star pi we shall find a good light test for our three-inch
aperture, the magnitudes being six and eleven, distance 22", p. 212 deg..
The four-inch will show that kappa is a double, magnitudes four and ten,
distance 6", p. 232 deg.. The smaller star is of a delicate blue color, and
it has been suspected of variability. That it may be variable is
rendered the more probable by the fact that in the immediate
neighborhood of kappa there are three undoubted variables, S, T, and U,
and there appears to be some mysterious law of association which causes
such stars to group themselves in certain regions. None of the variables
just named ever become visible to the naked eye, although they all
undergo great changes of brightness, sinking from the eighth or ninth
magnitude down to the thirteenth or even lower. The variable R, which
lies considerably farther west, is well worth attention because of the
remarkable change of color which it sometimes exhibits. It has been seen
blue, red, and yellow in succession. It varies from between the sixth
and seventh magnitudes to less than the thirteenth in a period of about
two hundred and forty-two days.
Not far away we find a still more curious variable zeta; this is also an
interesting triple star, its principal component being a little under
the third magnitude, while one of the companions is of the seventh
magnitude, distance 90", p. 355 deg., and the other is of the eleventh
magnitude or less, distance 65", p. 85 deg.. We should hardly expect to see
the fainter companion with the three-inch. The principal star varies
from magnitude three and seven tenths down to magnitude four and a half
in a period of a little more than ten days.
[Illustration: WONDERFUL NEBULA IN GEMINI (1532).]
With the four-or five-inch we get a very pretty sight in delta, which
appears split into a yellow and a purple star, magnitudes three and
eight, distance 7", p. 206 deg..
Near delta, toward the east, lies one of the strangest of all the
nebulae. (See the figures 1532 on the map.) Our telescopes will show it
to us only as a minute star surrounded with a nebulous atmosphere, but
its appearance with instruments of the first magnitude is so
astonishing and at the same time so beautiful that I can not refrain
from giving a brief description of it as I saw it in 1893 with the great
Lick telescope. In the center glittered the star, and spread evenly
around it was a circular nebulous disk, pale yet sparkling and
conspicuous. This disk was sharply bordered by a narrow _black_ ring,
and outside the ring the luminous haze of the nebula again appeared,
gradually fading toward the edge to invisibility. The accompanying cut,
which exaggerates the brightness of the nebula as compared with the
star, gives but a faint idea of this most singular object. If its
peculiarities were within the reach of ordinary telescopes, there are
few scenes in the heavens that would be deemed equally admirable.
In the star eta we have another long-period variable, which is also a
double star; unfortunately the companion, being of only the tenth
magnitude and distant less than 1" from its third-magnitude primary, is
beyond the reach of our telescopes. But eta points the way to one of the
finest star clusters in the sky, marked 1360 on the map. The naked eye
perceives that there is something remarkable in that place, and the
opera glass faintly reveals its distant splendors, but the telescope
fairly carries us into its presence. Its stars are innumerable, varying
from the ninth magnitude downward to the last limit of visibility, and
presenting a wonderful array of curves which are highly interesting from
the point of view of the nebular origin of such clusters. Looking
backward in time, with that theory to guide us, we can see spiral lines
of nebulous mist occupying the space that now glitters with interlacing
rows of stars. It is certainly difficult to understand how such lines of
nebula could become knotted with the nuclei of future stars, and then
gradually be absorbed into those stars; and yet, if such a process does
not occur, what is the meaning of that narrow nebulous streak in the
Pleiades along which five or six stars are strung like beads on a
string? The surroundings of this cluster, 1360, as one sweeps over them
with the telescope gradually drawing toward the nucleus, have often
reminded me of the approaches to such a city as London. Thicker and
closer the twinkling points become, until at last, as the observers eye
follows the gorgeous lines of stars trending inward, he seems to be
entering the streets of a brilliantly lighted metropolis.
Other objects in Gemini that we can ill miss are: , double, magnitudes
three and eleven, distance 73", p. 76 deg., colors yellow and blue; 15,
double, magnitudes six and eight, distance 33", p. 205 deg.; gamma,
remarkable for array of small stars near it; 38, double, magnitudes six
and eight, distance 6.5", p. 162 deg., colors yellow and blue (very pretty);
lambda, double, magnitudes four and eleven, distance 10", p. 30 deg., color
of larger star blue--try with the five-inch; epsilon, double, magnitudes
three and nine, distance 110", p. 94 deg..
From Gemini we pass to Cancer. This constellation has no large stars,
but its great cluster Praesepe (1681 on map No. 4) is easily seen as a
starry cloud with the naked eye. With the telescope it presents the most
brilliant appearance with a very low power. It was one of the first
objects that Galileo turned to when he had completed his telescope, and
he wonderingly counted its stars, of which he enumerated thirty-six, and
made a diagram showing their positions.
The most interesting star in Cancer is zeta, a celebrated triple. The
magnitudes of its components are six, seven, and seven and a half;
distances 1.14", p. 6 deg., and 5.7", p. 114 deg.. We must use our five-inch
glass in order satisfactorily to separate the two nearest stars. The
gravitational relationship of the three stars is very peculiar. The
nearest pair revolve around their common center in about fifty-eight
years, while the third star revolves with the other two, around a center
common to all three, in a period of six or seven hundred years. But the
movements of the third star are erratic, and inexplicable except upon
the hypothesis advanced by Seeliger, that there is an invisible, or
dark, star near it by whose attraction its motion is perturbed.
In endeavoring to picture the condition of things in zeta Cancri we
might imagine our sun to have a companion sun, a half or a third as
large as itself, and situated within what may be called planetary
distance, circling with it around their center of gravity; while a third
sun, smaller than the second and several times as far away, and
accompanied by a _black_ or non-luminous orb, swings with the first two
around another center of motion. There you would have an entertaining
complication for the inhabitants of a system of planets!
Other objects in Cancer are: Sigma 1223, double star, magnitudes six and
six and a half, distance 5", p. 214 deg.; Sigma 1291, double, magnitudes
both six, distance 1.3", p. 328 deg.--four-inch should split it; iota,
double, magnitudes four and a half and six and a half, distance 30", p.
308 deg.; 66, double magnitudes six and nine, distance 4.8", p. 136 deg.; Sigma
1311, double, magnitudes both about the seventh, distance 7", p. 200 deg.;
1712, star cluster, very beautiful with the five-inch glass.
[Illustration: MAP NO. 5.]
The constellation of Auriga may next command our attention (map No. 5).
The calm beauty of its leading star Capella awakens an admiration that
is not diminished by the rivalry of Orion's brilliants glittering to the
south of it. Although Capella must be an enormously greater sun than
ours, its spectrum bears so much resemblance to the solar spectrum that
a further likeness of condition is suggested. No close telescopic
companion to Capella has been discovered. A ninth-magnitude companion,
distant 159", p. 146 deg., and two others, one of twelfth magnitude at 78",
p. 317 deg., the other of thirteenth magnitude at 126", p. 183 deg., may be
distant satellites of the great star, but not planets in the ordinary
sense, since it is evident that they are self-luminous. It is a
significant fact that most of the first-magnitude stars have faint
companions which are not so distant as altogether to preclude the idea
of physical relationship.
But while Capella has no visible companion, Campbell, of the Lick
Observatory, has lately discovered that it is a conspicuous example of a
peculiar class of binary stars only detected within the closing decade
of the nineteenth century. The nature of these stars, called
spectroscopic binaries, may perhaps best be described while we turn our
attention from Capella to the second star in Auriga beta (Menkalina),
which not only belongs to the same class, but was the first to be
discovered. Neither our telescopes, nor any telescope in existence, can
directly reveal the duplicity of beta Aurigae to the eye--i. e., we can
not see the two stars composing it, because they are so close that their
light remains inextricably mingled after the highest practicable
magnifying power has been applied in the effort to separate them. But
the spectroscope shows that the star is double and that its components
are in rapid revolution around one another, completing their orbital
swing in the astonishingly short period of _four days_! The combined
mass of the two stars is estimated to be two and a half times the mass
of the sun, and the distance between them, from center to center, is
about eight million miles.
The manner in which the spectroscope revealed the existence of two
stars in beta Aurigae is a beautiful illustration of the unexpected and,
so to speak, automatic application of an old principle in the discovery
of new facts not looked for. It was noticed at the Harvard Observatory
that the lines in the photographed spectrum of beta Aurigae (and of a few
other stars to be mentioned later) appeared single in some of the
photographs and double in others. Investigation proved that the lines
were doubled at regular intervals of about two days, and that they
appeared single in the interim. The explanation was not far to seek. It
is known that all stars which are approaching us have their spectral
lines shifted, by virtue of their motion of approach, toward the violet
end of the spectrum, and that, for a similar reason, all stars which are
receding have their lines shifted toward the red end of the spectrum.
Now, suppose two stars to be revolving around one another in a plane
horizontal, or nearly so, to the line of sight. When they are at their
greatest angular distance apart as seen from the earth one of them will
evidently be approaching at the same moment that the other is receding.
The spectral lines of the first will therefore be shifted toward the
violet, and those of the second will be shifted toward the red. Then if
the stars, when at their greatest distance apart, are still so close
that the telescope can not separate them, their light will be combined
in the spectrum; but the spectral lines, being simultaneously shifted in
opposite directions, will necessarily appear to be doubled. As the
revolution of the stars continues, however, it is clear that their
motion will soon cease to be performed in the line of sight, and will
become more and more athwart that line, and as this occurs the spectral
lines will gradually assume their normal position and appear single.
This is the sequence of phenomena in beta Aurigae. And the same sequence
is found in Capella and in several other more or less conspicuous stars
in various parts of the heavens.
Such facts, like those connecting rows and groups of stars with masses
and spiral lines of nebula are obscure signboards, indicating the
opening of a way which, starting in an unexpected direction, leads deep
into the mysteries of the universe.
Southward from beta we find the star theta, which is a beautiful
quadruple. We shall do best with our five-inch here, although in a fine
condition of the atmosphere the four-inch might suffice. The primary is
of the third magnitude; the first companion is of magnitude seven and a
half, distance 2", p. 5 deg.; the second, of the tenth magnitude, distance
45", p. 292 deg.; and the third, of the tenth magnitude, distance 125", p.
350 deg..
We should look at the double Sigma 616 with one of our larger apertures
in order to determine for ourselves what the colors of the components
are. There is considerable diversity of opinion on this point. Some say
the larger star is pale red and the smaller light blue; others consider
the color of the larger star to be greenish, and some have even called
it white. The magnitudes are five and nine, distance 6", p. 350 deg..
Auriga contains several noteworthy clusters which will be found on the
map. The most beautiful of these is 1295, in which about five hundred
stars have been counted.
The position of the new star of 1892, known as Nova Aurigae, is also
indicated on the map. While this never made a brilliant appearance, it
gave rise to a greater variety of speculative theories than any previous
phenomenon of the kind. Although not recognized until January 24, 1892,
this star, as photographic records prove, was in existence on December
9, 1891. At its brightest it barely exceeded magnitude four and a half,
and its maximum occurred within ten days after its first recognition.
When discovered it was of the fifth magnitude. It was last seen in its
original form with the Lick telescope on April 26th, when it had sunk to
the lowest limit of visibility. To everybody's astonishment it
reappeared in the following August, and on the 17th of that month was
seen shining with the light of a tenth-magnitude star, _but presenting
the spectrum of a nebula!_ Its visual appearance in the great telescope
was now also that of a planetary nebula. Its spectrum during the first
period of its visibility had been carefully studied, so that the means
existed for making a spectroscopic comparison of the phenomenon in its
two phases. During the first period, when only a stellar spectrum was
noticed, remarkable shiftings of the spectral lines occurred, indicating
that two and perhaps three bodies were concerned in the production of
the light of the new star, one of which was approaching the earth, while
the other or the others receded with velocities of several hundred miles
per second! On the revival in the form of a planetary nebula, while the
character of the spectrum had entirely changed, evidences of rapid
motion in the line of sight remained.
But what was the meaning of all this? Evidently a catastrophe of some
kind had occurred out there in space. The idea of a collision involving
the transformation of the energy of motion into that of light and heat
suggests itself at once. But what were the circumstances of the
collision? Did an extinguished sun, flying blindly through space, plunge
into a vast cloud of meteoric particles, and, under the lashing impact
of so many myriads of missiles, break into superficial incandescence,
while the cosmical wrack through which it had driven remained glowing
with nebulous luminosity? Such an explanation has been offered by
Seeliger. Or was Vogel right when he suggested that Nova Aurigae could
be accounted for by supposing that a wandering dark body had run into
collision with a system of planets surrounding a decrepit sun (and
therefore it is to be hoped uninhabited), and that those planets had
been reduced to vapor and sent spinning by the encounter, the second
outburst of light being caused by an outlying planet of the system
falling a prey to the vagabond destroyer? Or some may prefer the
explanation, based on a theory of Wilsing's, that _two_ great bodies,
partially or wholly opaque and non-luminous at their surfaces, but
liquid hot within, approached one another so closely that the tremendous
strain of their tidal attraction burst their shells asunder so that
their bowels of fire gushed briefly visible, amid a blaze of spouting
vapors. And yet Lockyer thinks that there was no solid or semisolid mass
concerned in the phenomenon at all, but that what occurred was simply
the clash of two immense swarms of meteors that had crossed one
another's track.
Well, where nobody positively knows, everybody has free choice. In the
meantime, look at the spot in the sky where that little star made its
appearance and underwent its marvelous transformation, for, even if you
can see no remains of it there, you will feel your interest in the
problem it has presented, and in the whole subject of astronomy, greatly
heightened and vivified, as the visitor to the field of Waterloo becomes
a lover of history on the spot.
The remaining objects of special interest in Auriga may be briefly
mentioned: 26, triple star, magnitudes five, eight, and eleven,
distances 12", p. 268 deg., and 26", p. 113 deg.; 14, triple star, magnitudes
five, seven and a half, and eleven, distances 14", p. 224 deg., and 12.6",
p. 342 deg., the last difficult for moderate apertures; lambda, double,
magnitudes five and nine, distance 121", p. 13 deg.; epsilon, variable,
generally of third magnitude, but has been seen of only four and a half
magnitude; 41, double, magnitudes five and six, distance 8", p. 354 deg.;
996, 1067, 1119, and 1166, clusters all well worth inspection, 1119
being especially beautiful.
The inconspicuous Lynx furnishes some fine telescopic objects, all
grouped near the northwestern corner of the constellation. Without a
six-inch telescope it would be a waste of time to attack the double star
4, whose components are of sixth and eighth magnitudes, distance 0.8",
p. 103 deg.; but its neighbor, 5, a fine triple, is within our reach, the
magnitudes being six, ten, and eight, distances 30", p. 139 deg., and 96",
p. 272 deg.. In 12 Lyncis we find one of the most attractive of triple
stars, which in good seeing weather is not beyond the powers of a
three-inch glass, although we shall have a far more satisfactory view of
it with the four-inch. The components are of the sixth, seventh, and
eighth magnitudes, distances 1.4", p. 117 deg., and 8.7", p. 304 deg.. A
magnifying power which just suffices clearly to separate the disks of
the two nearer stars makes this a fine sight. A beautiful contrast of
colors belongs to the double star 14, but unfortunately the star is at
present very close, the distance between its sixth and seventh magnitude
components not exceeding 0.8", position angle 64 deg.. Sigma 958 is a pretty
double, both stars being of the sixth magnitude, distance 5", p. 257 deg..
Still finer is Sigma 1009, a double, whose stars are both a little above
the seventh magnitude and nearly equal, distance 3", p. 156 deg.. A low
power suffices to show the three stars in 19, their magnitudes being six
and a half, seven and a half, and eight, distances 15", p. 312 deg., and
215", p. 358 deg.. Webb describes the two smaller stars as plum-colored.
Plum-colored suns!
At the opposite end of the constellation are two fine doubles, Sigma
1333, magnitudes six and a half and seven, distance 1.4", p. 39 deg.; and
38, magnitudes four and seven, distance 2.9", p. 235 deg..
Under the guidance of map No. 6 we turn to Leo, which contains one of
the leading gems among the double stars, gamma, whose components, of the
second and fourth magnitudes, are respectively yellow and green, the
green star, according to some observers, having a peculiar tinge of red.
Their distance apart is 3.7", p. 118 deg., and they are undoubtedly in
revolution about a common center, the probable period being about four
hundred years. The three-inch glass should separate them easily when the
air is steady, and a pleasing sight they are.
The star iota is a closer double, and also very pretty, magnitudes four
and eight, colors lemon and light blue, distance 2.17", p. 53 deg.. Other
doubles are tau, magnitudes five and seven, distance 95", p. 170 deg.; 88,
magnitudes seven and nine, distance 15", p. 320 deg.; 90, triple, magnitudes
six, seven and a half, and ten, distance, 3.5", p. 209 deg., and 59", p.
234 deg.; 54, magnitudes four and a half and seven, distance 6.2", p. 102 deg.;
and 49, magnitudes six and nine, distance 2.4", p. 158 deg..
Leo contains a remarkable variable star, R, deep red in color, and
varying in a space of a hundred and forty-four days from the fifth to
the tenth magnitude. It has also several nebulae, of which only one needs
special mention, No. 1861. This is spindle-shaped, and large telescopes
show that it consists of three nebulae. The observer with ordinary
instruments finds little to see and little to interest him in these
small, faint nebulae.
We may just glance at two double stars in the small constellation of
Sextans, situated under Leo. These are: 9, magnitudes seven and eight,
distance 53", p. 292 deg.; and 35, magnitudes six and seven, distance 6.9",
p. 240 deg..
[Illustration: MAP NO. 6.]
Coma Berenices (map No. 6) includes several interesting objects. Let
us begin with the star 2, a double, of magnitudes six and seven and a
half, distance 3.6", p. 240 deg.. The color of the smaller star is lilac.
This hue, although not extremely uncommon among double stars elsewhere,
recurs again and again, with singular persistence, in this little
constellation. For instance, in the very next star that we look at, 12,
we find a double whose smaller component is _lilac_. The magnitudes in
12 are five and eight, distance 66", p. 168 deg.. So also the wide double
17, magnitudes five and a half and six, distance 145", exhibits a tinge
of _lilac_ in the smaller component; the triple 35, magnitudes five,
eight, and nine, distances 1", p. 77 deg., and 28.7", p. 124 deg., has four
colors yellow, _lilac_, and blue, and the double 24, magnitudes five and
six, distance 20", p. 270 deg., combines an orange with a _lilac_ star, a
very striking and beautiful contrast. We should make a mistake if we
regarded this wonderful distribution of color among the double stars as
accidental. It is manifestly expressive of their physical condition,
although we can not yet decipher its exact meaning.
The binary 42 Comae Berenicis is too close for ordinary telescopes, but
it is highly interesting as an intermediate between those pairs which
the telescope is able to separate and those--like beta Aurigae--which no
magnifying power can divide, but which reveal the fact that they are
double by the periodical splitting of their spectral lines. The orbit in
42 Comae Berenicis is a very small one, so that even when the components
are at their greatest distance apart they can not be separated by a
five-or six-inch glass. Burnham, using the Lick telescope, in 1890 made
the distance 0.7"; Hall, using the Washington telescope, in 1891 made it
a trifle more than 0.5". He had measured it in 1886 as only 0.27". The
period of revolution is believed to be about twenty-five years.
In Coma Berenices there is an outlying field of the marvelous nebulous
region of Virgo, which we may explore on some future evening. But the
nebulae in Coma are very faint, and, for an amateur, hardly worth the
trouble required to pick them up. The two clusters included in the map,
2752 and 3453, are bright enough to repay inspection with our largest
aperture.
[Illustration: MAP NO. 7.]
Although Hydra is the largest constellation in the heavens, extending
about seven hours, or 105 deg., in right ascension, it contains
comparatively few objects of interest, and most of these are in the head
or western end of the constellation, which we examined during our first
night at the telescope. In the central portion of Hydra, represented on
map No. 7, we find its leading star alpha, sometimes called Alphard, or
Cor Hydrae, a bright second-magnitude star that has been suspected of
variability. It has a decided orange tint, and is accompanied, at a
distance of 281", p. 153 deg., by a greenish tenth-magnitude star. Bu. 339
is a fine double, magnitudes eight and nine and a half, distance 1.3",
p. 216 deg.. The planetary nebula 2102 is about 1' in diameter, pale blue in
color, and worth looking at, because it is brighter than most objects of
its class. Tempel and Secchi have given wonderful descriptions of it,
both finding multitudes of stars intermingled with nebulous matter.
For a last glimpse at celestial splendors for the night, let us turn to
the rich cluster 1630, in Argo, just above the place where the stream of
the Milky Way--here bright in mid-channel and shallowing toward the
shores--separates into two or three currents before disappearing behind
the horizon. It is by no means as brilliant as some of the star clusters
we have seen, but it gains in beauty and impressiveness from the
presence of one bright star that seems to captain a host of inferior
luminaries.