FROM LYRA TO ERIDANUS
"This Orpheus struck when with his wondrous song
He charmed the woods and drew the rocks along."--MANILIUS.
[Illustration: MAP NO. 17.]
We resume our celestial explorations with the little constellation Lyra,
whose chief star, Vega (alpha), has a very good claim to be regarded as
the most beautiful in the sky. The position of this remarkable star is
indicated in map No. 17. Every eye not insensitive to delicate shades of
color perceives at once that Vega is not white, but blue-white. When the
telescope is turned upon the star the color brightens splendidly.
Indeed, some glasses decidedly exaggerate the blueness of Vega, but the
effect is so beautiful that one can easily forgive the optical
imperfection which produces it. With our four-inch we look for the
well-known companion of Vega, a tenth-magnitude star, also of a blue
color deeper than the hue of its great neighbor. The distance is 50", p.
158 deg.. Under the most favorable circumstances it might be glimpsed with
the three-inch, but, upon the whole, I should regard it as too severe a
test for so small an aperture.
Vega is one of those stars which evidently are not only enormously
larger than the sun (one estimate makes the ratio in this case nine
hundred to one), but whose physical condition, as far as the
spectroscope reveals it, is very different from that of our ruling orb.
Like Sirius, Vega displays the lines of hydrogen most conspicuously, and
it is probably a much hotter as well as a much more voluminous body
than the sun.
Close by, toward the east, two fourth-magnitude stars form a little
triangle with Vega. Both are interesting objects for the telescope, and
the northern one, epsilon, has few rivals in this respect. Let us first
look at it with an opera glass. The slight magnifying power of such an
instrument divides the star into two twinkling points. They are about
two and a quarter minutes of arc apart, and exceptionally sharp-sighted
persons are able to see them divided with the naked eye. Now take the
three-inch telescope and look at them, with a moderate power. Each of
the two stars revealed by the opera glass appears double, and a fifth
star of the ninth magnitude is seen on one side of an imaginary line
joining the two pairs. The northern-most pair is named epsilon_1, the
magnitudes being fifth and sixth, distance 3", p. 15 deg.. The other pair is
epsilon_2, magnitudes fifth and sixth, distance 2.3", p. 133 deg.. Each pair
is apparently a binary; but the period of revolution is unknown. Some
have guessed a thousand years for one pair, and two thousand for the
other. Another guess gives epsilon_1 a period of one thousand years, and
epsilon_2 a period of eight hundred years. Hall, in his double-star
observations, simply says of each, "A slow motion."
Purely by guesswork a period has also been assigned to the two pairs in
a supposed revolution around their common center, the time named being
about a million years. It is not known, however, that such a motion
exists. Manifestly it could not be ascertained within the brief period
during which scientific observations of these stars have been made. The
importance of the element of time in the study of stellar motions is
frequently overlooked, though not, of course, by those who are engaged
in such work. The sun, for instance, and many of the stars are known
to be moving in what appear to be straight lines in space, but
observations extending over thousands of years would probably show that
these motions are in curved paths, and perhaps in closed orbits.
If now in turn we take our four-inch glass, we shall see something else
in this strange family group of epsilon Lyrae. Between epsilon_1 and
epsilon_2, and placed one on each side of the joining line, appear two
exceedingly faint specks of light, which Sir John Herschel made famous
under the name of the _debillissima_. They are of the twelfth or
thirteenth magnitude, and possibly variable to a slight degree. If you
can not see them at first, turn your eye toward one side of the field of
view, and thus, by bringing their images upon a more sensitive part of
the retina, you may glimpse them. The sight is not much, yet it will
repay you, as every glance into the depths of the universe does.
The other fourth-magnitude star near Vega is zeta, a wide double,
magnitudes fourth and sixth, distance 44", p. 150 deg.. Below we find beta,
another very interesting star, since it is both a multiple and an
eccentric variable. It has four companions, three of which we can easily
see with our three-inch; the fourth calls for the five-inch; the
magnitudes are respectively four, seven or under, eight, eight and a
half, and eleven; distances 45", p. 150 deg.; 65", p. 320 deg.; 85", p. 20 deg.; and
46", p. 248 deg.. The primary, beta, varies from about magnitude three and a
half to magnitude four and a half, the period being twelve days,
twenty-one hours, forty-six minutes, and fifty-eight seconds. Two
unequal maxima and minima occur within this period. In the spectrum of
this star some of the hydrogen lines and the D_3 line (the latter
representing helium, a constituent of the sun and of some of the stars,
which, until its recent discovery in a few rare minerals was not known
to exist on the earth) are bright, but they vary in visibility.
Moreover, dark lines due to hydrogen also appear in its spectrum
simultaneously with the bright lines of that element. Then, too, the
bright lines are sometimes seen double. Professor Pickering's
explanation is that beta Lyrae probably consists of two stars, which,
like the two composing beta Aurigae, are too close to be separated with
any telescope now existing, and that the body which gives the bright
lines is revolving in a circle in a period of about twelve days and
twenty-two hours around the body which gives the dark lines. He has also
suggested that the appearances could be accounted for by supposing a
body like our sun to be rotating in twelve days and twenty-two hours,
and having attached to it an enormous protuberance extending over more
than one hundred and eighty degrees of longitude, so that when one end
of it was approaching us with the rotation of the star the other end
would be receding, and a splitting of the spectral lines at certain
periods would be the consequence. "The variation in light," he adds,
"may be caused by the visibility of a larger or smaller portion of this
protuberance."
Unfortunate star, doomed to carry its parasitical burden of hydrogen and
helium, like Sindbad in the clasp of the Old Man of the Sea! Surely, the
human imagination is never so wonderful as when it bears an astronomer
on its wings. Yet it must be admitted that the facts in this case are
well calculated to summon the genius of hypothesis. And the puzzle is
hardly simplified by Belopolsky's observation that the body in beta Lyrae
giving dark hydrogen lines shows those lines also split at certain
times. It has been calculated, from a study of the phenomena noted
above, that the bright-line star in beta Lyrae is situated at a distance
of about fifteen million miles from the center of gravity of the
curiously complicated system of which it forms a part.
We have not yet exhausted the wonders of Lyra. On a line from beta to
gamma, and about one third of the distance from the former to the
latter, is the celebrated Ring Nebula, indicated on the map by the
number 4447. We need all the light we can get to see this object well,
and so, although the three-inch will show it, we shall use the
five-inch. Beginning with a power of one hundred diameters, which
exhibits it as a minute elliptical ring, rather misty, very soft and
delicate, and yet distinct, we increase the magnification first to two
hundred and finally to three hundred, in order to distinguish a little
better some of the details of its shape. Upon the whole, however, we
find that the lowest power that clearly brings out the ring gives the
most satisfactory view. The circumference of the ring is greater than
that of the planet Jupiter. Its ellipticity is conspicuous, the length
of the longer axis being 78" and that of the shorter 60". Closely
following the nebula as it moves through the field of view, our
five-inch telescope reveals a faint star of the eleventh or twelfth
magnitude, which is suspected of variability. The largest instruments,
like the Washington and the Lick glasses, have shown perhaps a dozen
other stars apparently connected with the nebula. A beautiful sparkling
effect which the nebula presents was once thought to be an indication
that it was really composed of a circle of stars, but the spectroscope
shows that its constitution is gaseous. Just in the middle of the open
ring is a feeble star, a mere spark in the most powerful telescope. But
when the Ring Nebula is photographed--and this is seen beautifully in
the photographs made with the Crossley reflector on Mount Hamilton by
the late Prof. J. E. Keeler--this excessively faint star imprints its
image boldly as a large bright blur, encircled by the nebulous ring,
which itself appears to consist of a series of intertwisted spirals.
Not far away we find a difficult double star, 17, whose components are
of magnitudes six and ten or eleven, distance 3.7", p. 325 deg..
From Lyra we pass to Cygnus, which, lying in one of the richest parts of
the Milky Way, is a very interesting constellation for the possessor of
a telescope. Its general outlines are plainly marked for the naked eye
by the figure of a cross more than twenty degrees in length lying along
the axis of the Milky Way. The foot of the cross is indicated by the
star beta, also known as Albireo, one of the most charming of all the
double stars. The three-inch amply suffices to reveal the beauty of this
object, whose components present as sharp a contrast of light yellow and
deep blue as it would be possible to produce artificially with the
purest pigments. The magnitudes are three and seven, distance 34.6", p.
55 deg.. No motion has been detected indicating that these stars are
connected in orbital revolution, yet no one can look at them without
feeling that they are intimately related to one another. It is a sight
to which one returns again and again, always with undiminished pleasure.
The most inexperienced observer admires its beauty, and after an hour
spent with doubtful results in trying to interest a tyro in double stars
it is always with a sense of assured success that one turns the
telescope to beta Cygni.
Following up the beam of the imaginary cross along the current of the
Milky Way, every square degree of which is here worth long gazing into,
we come to a pair of stars which contend for the name-letter chi. On our
map the letter is attached to the southernmost of the two, a variable of
long period--four hundred and six days--whose changes of brilliance lie
between magnitudes four and thirteen, but which exhibits much
irregularity in its maxima. The other star, not named but easily
recognized in the map, is sometimes called 17. It is an attractive
double whose colors faintly reproduce those of beta. The magnitudes are
five and eight, distance 26", p. 73 deg.. Where the two arms of the cross
meet is gamma, whose remarkable _cortege_ of small stars running in
curved streams should not be missed. Use the lowest magnifying power.
At the extremity of the western arm of the cross is delta, a close
double, difficult for telescopes of moderate aperture on account of the
difference in the magnitudes of the components. We may succeed in
dividing it with the five-inch. The magnitudes are three and eight,
distance 1.5", p. 310 deg.. It is regarded as a binary of long and as yet
unascertained period.
In omicron^2 we find a star of magnitude four and orange in color,
having two blue companions, the first of magnitude seven and a half,
distance 107", p. 174 deg., and the second of magnitude five and a half,
distance 358", p. 324 deg.. Farther north is psi, which presents to us the
combination of a white five-and-a-half-magnitude star with a lilac star
of magnitude seven and a half. The distance is 3", p. 184 deg.. A very
pretty sight.
We now pass to the extremity of the other arm of the cross, near which
lies the beautiful little double 49, whose components are of magnitudes
six and eight, distance 2.8", p. 50 deg.. The colors are yellow and blue,
conspicuous and finely contrasted. A neighboring double of similar hues
is 52, in which the magnitudes are four and nine, distance 6", p. 60 deg..
Sweeping a little way northward we come upon an interesting binary,
lambda, which is unfortunately beyond the dividing power of our largest
glass. A good seven-inch or seven-and-a-half-inch should split it under
favorable circumstances. Its magnitudes are six and seven, distance
0.66", p. 74 deg..
The next step carries us to a very famous object, 61 Cygni, long known
as the nearest star in the northern hemisphere of the heavens. It is a
double which our three-inch will readily divide, the magnitudes being
both six, distance 21", p. 122 deg.. The distance of 61 Cygni, according to
Hall's parallax of 0.27", is about 70,000,000,000,000 miles. There is
some question whether or not it is a binary, for, while the twin stars
are both moving in the same direction in space with comparative
rapidity, yet conclusive evidence of orbital motion is lacking. When one
has noticed the contrast in apparent size between this comparatively
near-by star, which the naked eye only detects with considerable
difficulty, and some of its brilliant neighbors whose distance is so
great as to be immeasurable with our present means, no better proof will
be needed of the fact that the faintness of a star is not necessarily an
indication of remoteness.
We may prepare our eyes for a beautiful exhibition of contrasted colors
once more in the star . This is really a quadruple, although only two of
its components are close and conspicuous. The magnitudes are five, six,
seven and a half, and twelve; distances 2.4", p. 121 deg.; 208", p. 56 deg.; and
35", p. 264 deg.. The color of the largest star is white and that of its
nearest companion blue; the star of magnitude seven and a half is also
blue.
The star cluster 4681 is a fine sight with our largest glass. In the map
we find the place marked where the new star of 1876 made its appearance.
This was first noticed on November 24, 1876, when it shone with the
brilliance of a star of magnitude three and a half. Its spectrum was
carefully studied, especially by Vogel, and the very interesting changes
that it underwent were noted. Within a year the star had faded to less
than the tenth magnitude, and its spectrum had completely changed in
appearance, and had come to bear a close resemblance to that of a
planetary nebula. This has been quoted as a possible instance of a
celestial collision through whose effects the solid colliding masses
were vaporized and expanded into a nebula. At present the star is very
faint and can only be seen with the most powerful telescopes. Compare
with the case of Nova Aurigae, previously discussed.
Underneath Cygnus we notice the small constellation Vulpecula. It
contains a few objects worthy of attention, the first being the nebula
4532, the "dumb-bell nebula" of Lord Rosse. With the four-inch, and
better with the five-inch, we are able to perceive that it consists of
two close-lying tufts of misty light. Many stars surround it, and large
telescopes show them scattered between the two main masses of the
nebula. The Lick photographs show that its structure is spiral. The star
11 points out the place where a new star of the third magnitude appeared
in 1670. Sigma 2695 is a close double, magnitudes six and eight,
distance 0.96", p. 78 deg..
[Illustration: MAP NO. 18.]
We turn to map No. 18, and, beginning at the western end of the
constellation Aquarius, we find the variable T, which ranges between
magnitudes seven and thirteen in a period of about two hundred and three
days. Its near neighbor Sigma 2729 is a very close double, beyond the
separating power of our five-inch, the magnitudes being six and seven,
distance 0.6", p. 176 deg.. Sigma 2745, also known as 12 Aquarii, is a good
double for the three-inch. Its magnitudes are six and eight, distance
2.8", p. 190 deg.. In zeta we discover a beauty. It is a slow binary of
magnitudes four and four, distance 3.1", p. 321 deg.. According to some
observers both stars have a greenish tinge. The star 41 is a wider
double, magnitudes six and eight, distance 5", p. 115 deg., colors yellow
and blue. The uncommon stellar contrast of white with light garnet is
exhibited by tau, magnitudes six and nine, distance 27", p. 115 deg.. Yellow
and blue occur again conspicuously in psi, magnitudes four and a half
and eight and a half, distance 50", p. 310 deg.. Rose and emerald have been
recorded as the colors exhibited in Sigma 2998, whose magnitudes are
five and seven, distance 1.3", p. 346 deg..
The variables S and R are both red. The former ranges between magnitudes
eight and twelve, period two hundred and eighty days, and the latter
between magnitudes six and eleven, period about three hundred and ninety
days.
The nebula 4628 is Rosse's "Saturn nebula," so called because with his
great telescope it presented the appearance of a nebulous model of the
planet Saturn. With our five-inch we see it simply as a planetary
nebula. We may also glance at another nebula, 4678, which appears
circular and is pinned with a little star at the edge.
The small constellation Equuleus contains a surprisingly large number of
interesting objects. Sigma 2735 is a rather close double, magnitudes six
and eight, distance 1.8", p. 287 deg.. Sigma 2737 (the first star to the
left of Sigma 2735, the name having accidentally been omitted from the
map) is a beautiful triple, although the two closest stars, of
magnitudes six and seven, can not be separated by our instruments. Their
distance in 1886 was 0.78", p. 286 deg., and they had then been closing
rapidly since 1884, when the distance was 1.26". The third star, of
magnitude eight, is distant 11", p. 75 deg.. Sigma 2744 consists of two
stars, magnitudes six and seven, distance 1.4", p. 1.67 deg.. It is probably
a binary. Sigma 2742 is wider double, magnitudes both six, distance
2.6", p. 225 deg.. Another triple, one of whose components is beyond our
reach, is gamma. Here the magnitudes are fifth, twelfth, and sixth,
distances 2", p. 274 deg. and 366". It would also be useless for us to try
to separate delta, but it is interesting to remember that this is one of
the closest of known double stars, the magnitudes being fourth and
fifth, distance 0.4", p. 198 deg.. These data are from Hall's measurements
in 1887. The star is, no doubt, a binary. With the five-inch we may
detect one and perhaps two of the companion stars in the quadruple beta.
The magnitudes are five, ten, and two eleven, distances 67", p. 309 deg.;
86", p. 276 deg.; and 6.5", p. 15 deg.. The close pair is comprised in the
tenth-magnitude star.
[Illustration: MAP NO. 19.]
Map No. 19 introduces us to the constellation Pegasus, which is
comparatively barren to the naked eye, and by no means rich in
telescopic phenomena. The star epsilon, of magnitude two and a half, has
a blue companion of the eighth magnitude, distance 138", p. 324 deg.; colors
yellow and violet. A curious experiment that may be tried with this star
is described by Webb, who ascribes the discovery of the phenomenon to
Sir John Herschel. When near the meridian the small star in epsilon
appears, in the telescope, underneath the large one. If now the tube of
the telescope be slightly swung from side to side the small star will
appear to describe a pendulumlike movement with respect to the large
one. The explanation suggested is that the comparative faintness of the
small star causes its light to affect the retina of the eye less quickly
than does that of its brighter companion, and, in consequence, the
reversal of its apparent motion with the swinging of the telescope is
not perceived so soon.
The third-magnitude star eta has a companion of magnitude ten and a
half, distance 90", p. 340 deg.. The star beta, of the second magnitude, and
reddish, is variable to the extent of half a magnitude in an irregular
period, and gamma, of magnitude two and a half, has an
eleventh-magnitude companion, distance 162", p. 285 deg..
[Illustration: MAP NO. 20.]
Our interest is revived on turning, with the guidance of map No. 20,
from the comparative poverty of Pegasus to the spacious constellation
Cetus. The first double star that we meet in this constellation is 26,
whose components are of magnitudes six and nine, distance 16.4", p.
252 deg.; colors, topaz and lilac. Not far away is the closer double 42,
composed of a sixth and a seventh magnitude star, distance 1.25", p.
350 deg.. The four-inch is capable of splitting this star, but we shall do
better to use the five-inch. In passing we may glance at the
tenth-magnitude companion to eta, distance 225", p. 304 deg.. Another wide
pair is found in zeta, magnitudes three and nine, distance 185", p. 40 deg..
The next step brings us to the wonderful variable omicron, or Mira,
whose changes have been watched for three centuries, the first observer
of the variability of the star having been David Fabricius in 1596. Not
only is the range of variability very great, but the period is
remarkably irregular. In the time of Hevelius, Mira was once invisible
for four years. When brightest, the star is of about the second
magnitude, and when faintest, of the ninth magnitude, but at maximum it
seldom exhibits the greatest brilliance that it has on a few occasions
shown itself capable of attaining. Ordinarily it begins to fade after
reaching the fourth or fifth magnitude. The period averages about three
hundred and thirty-one days, but is irregularly variable to the extent
of twenty-five days. Its color is red, and its spectrum shows bright
lines, which it is believed disappear when the star sinks to a minimum.
Among the various theories proposed to account for such changes as these
the most probable appears to be that which ascribes them to some cause
analogous to that operating in the production of sun spots. The
outburst of light, however, as pointed out by Scheiner, should be
regarded as corresponding to the maximum and not the minimum stage of
sun-spot activity. According to this view, the star is to be regarded as
possessing an extensive atmosphere of hydrogen, which, during the
maximum, is upheaved into enormous prominences, and the brilliance of
the light from these prominences suffices to swamp the photospheric
light, so that in the spectrum the hydrogen lines appear bright instead
of dark.
It is not possible to suppose that Mira can be the center of a system of
habitable planets, no matter what we may think of the more constant
stars in that regard, because its radiation manifestly increases more
than six hundred fold, and then falls off again to an equal extent once
in every ten or eleven months. I have met people who can not believe
that the Almighty would make a sun and then allow its energies "to go to
waste," by not supplying it with a family of worlds. But I imagine that
if they had to live within the precincts of Mira Ceti they would cry out
for exemption from their own law of stellar utility.
The most beautiful double star in Cetus is gamma, magnitudes three and
seven, distance 3", p. 288 deg.; hues, straw-color and blue. The leading
star alpha, of magnitude two and a half, has a distant blue companion
three magnitudes fainter, and between them are two minute stars, the
southernmost of which is a double, magnitudes both eleven, distance 10",
p. 225 deg..
The variable S ranges between magnitudes seven and twelve in a somewhat
irregular period of about eleven months, while R ranges between the
seventh and the thirteenth magnitudes in a period of one hundred and
sixty-seven days.
[Illustration: MAP NO. 21.]
The constellation Eridanus, represented in map No. 21, contains a few
fine double stars, one of the most interesting of which is 12, a rather
close binary. The magnitudes are four and eight, distance 2", p. 327 deg..
We shall take the five-inch for this, and a steady atmosphere and sharp
seeing will be necessary on account of the wide difference in the
brightness of the component stars. Amateurs frequently fail to make due
allowance for the effect of such difference. When the limit of
separating power for a telescope of a particular aperture is set at 1"
or 2", as the case may be, it is assumed that the stars composing the
doubles on which the test is made shall be of nearly the same magnitude,
or at least that they shall not differ by more than one or two
magnitudes at the most. The stray light surrounding a comparatively
bright star tends to conceal a faint companion, although the telescope
may perfectly separate them so far as the stellar disks are concerned.
Then, too, I have observed in my own experience that a very faint and
close double is more difficult than a brighter pair not more widely
separated, usually on account of the defect of light, and this is true
even when the components of the faint double are of equal magnitude.
Sigma 470, otherwise known as 32 Eridani, is a superb object on account
of the colors of its components, the larger star being a rich topaz and
the smaller an ultramarine; while the difference in magnitude is not as
great as in many of the colored doubles. The magnitudes are five and
seven, distance 6.7", p. 348 deg.. The star gamma, of magnitude two and a
half, has a tenth-magnitude companion, distant 51", p. 238 deg.. Sigma 516,
also called 39 Eridani, consists of two stars of magnitudes six and
nine, distance 6.4", p. 150 deg.; colors, yellow and blue. The supposed
binary character of this star has not yet been established.
In omicron^2 we come upon an interesting triple star, two of whose
components at any rate we can easily see. The largest component is of
the fourth magnitude. At a distance of 82", p. 105 deg., we find a
tenth-magnitude companion. This companion is itself double, the
magnitudes of its components being ten and eleven, distance 2.6", p.
98 deg.. Hall says of these stars that they "form a remarkable system." He
has also observed a fourth star of the twelfth magnitude, distant 45"
from the largest star, p. 85 deg.. This is apparently unconnected with the
others, although it is only half as distant as the tenth-magnitude
component is from the primary. Sigma 590 is interesting because of the
similarity of its two components in size, both being of about the
seventh magnitude, distance 10", p. 318 deg..
Finally, we turn to the nebula 826. This is planetary in form and
inconspicuous, but Lassell has described it as presenting a most
extraordinary appearance with his great reflector--a circular nebula
lying upon another fainter and larger nebula of a similar shape, and
having a star in its center. Yet it may possibly be an immensely distant
star cluster instead of a nebula, since its spectrum does not appear to
be gaseous.