SOME PARTICULAR SUNS.
In the constellation of the Swan there is a little, dim,
sixth-magnitude star, scarcely to be seen without a telescope. This
star, 61 Cygni by name, is the first whose distance from us it was
found possible to determine.
We may think it strange that so faint a star was even attempted.
Would not astronomers have naturally supposed it to be one of the
farther-distant stars? No, they did not. For though 61 Cygni showed but
a dim light, yet his motion--not the daily apparent motion, but the
real motion as seen from earth--was found to be so much more rapid than
the motion of most other stars that they rightly guessed 61 Cygni to be
a rather near neighbor of ours.
Do not misunderstand me, when I speak of a “more rapid motion,” and of
“rather near neighborhood.” The real rate of 61 Cygni’s rush through
space is believed to be about forty miles each second, or one thousand
four hundred and fifty millions of miles each year. All we can perceive
of this quick motion is that, in the course of three hundred and fifty
years, 61 Cygni travels over a space in the sky about as long as the
breadth of the full moon. Little enough, yet very far beyond what can
be detected in the greater number of even the brightest stars.
Then, again, as to the near neighborhood of this star, 61 Cygni is
near enough to have his distance measured, and that is saying a good
deal. Alpha Centauri, the nearest star of which we know in the southern
heavens, is two hundred and seventy-five thousand times as far distant
as the sun. But 61 Cygni, the nearest star of which we know in the
northern heavens, is nearly twice as far away as Alpha Centauri.
[Illustration: CYGNUS.]
We call 61 Cygni a star, for so he appears to common observers. In
reality, instead of being only one star, the speck of light which
we call 61 Cygni consists of _two stars_. The two are separated by
a gap about half as wide again as the wide gap between the sun and
Neptune. Yet so great is their distance from us that to the naked eye
the two seem to be one. These two suns would together make a sun only
about one-third as large as our sun. They differ in size, the quicker
movements of one showing it to be the smaller; and it is by means of
their known distance from one another, and their known rate of motion,
that their size, or rather their weight, can be roughly calculated. Of
course neither of the two shows any actual measurable disk. So much and
so little is with tolerable certainty known about this particular pair
of suns.
Next let us turn to Alpha Centauri--named _Alpha_, the first
letter of the Greek alphabet, because it is the brightest star in
the constellation of the Centaur. The second brightest star in a
constellation is generally called Beta, the third Gamma, the fourth
Delta, and so on; just as if we were to name them A, B, C, D, in order
of brightness.
The constellation Centaur lies in the southern heavens, close to the
beautiful constellation called the Southern Cross, and is invisible in
the northern hemisphere. Of all the stars shining in the heavens round
our earth, two only--Sirius and Canopus--show greater brilliancy than
Alpha Centauri.
As in the case of 61 Cygni, astronomers were led to attempt the
measurement of Alpha Centauri’s distance, by noticing how much more
distinct were his movements than the movements of other stars, though
less rapid both to the eye and in reality than those of 61 Cygni. Alpha
Centauri’s rate of motion is some thirteen miles each second.
And this, so far as we yet know, is our sun’s nearest neighbor in the
heavens outside his own family circle.
Strange to say, Alpha Centauri, like 61 Cygni, consists, not of a
single star, but of a pair of stars. It is a two-sun system--whether or
no surrounded by planets can not be told. We can only reason from what
we see to what we do not see. And as God did not form our earth “in
vain,” and did not form our sun “in vain,” so we firmly believe that he
did not form “in vain” any one of his myriads of suns scattered through
space. What is, has been, or will be the particular use of each one,
it would be rash to attempt to say. But that many among them have,
like our own sun, systems of worlds revolving round them, we may safely
consider very probable.
[Illustration: STARS WHOSE DISTANCES ARE BEST KNOWN. (See Table.)]
The two suns of the Alpha Centauri double-star are separated by a
distance about twenty-two times as great as the distance of the earth
from the sun, yet to the naked eye they show as a single star. Here
again one is much smaller than the other; and the smaller revolves
round the larger in about eighty-five years.
It is believed that the two together would form a sun about twice as
large and heavy as our sun. This belief is strengthened by the great
brilliancy of Alpha Centauri. Our own sun, placed at that distance from
us, would shine only one-third as brightly as he does.
STARS WHOSE DISTANCES ARE BEST KNOWN.
+--+--------------------+----------+------------------+
| | NAME OF STAR. |MAGNITUDE.|DISTANCE IN MILES.|
+--+--------------------+----------+------------------+
| 1| Alpha Centauri, | 1.0 | 25 trillions. |
| 2| 61 Cygni, | 5.1 | 43 ” |
| 3| 2,398, Draco, | 8.2 | 55 ” |
| 4| Sirius, | 1.0 | 58 ” |
| 5| 9,352, Lacaille, | 7.5 | 66 ” |
| 6| Procyon, | 1.3 | 71 ” |
| 7| Lalande, 21,258, | 8.5 | 74 ” |
| 8| Œltzen, 11,677, | 9.0 | 74 ” |
| 9| Sigma Draconis, | 4.7 | 78 ” |
|10| Aldebaran, | 1.5 | 81 ” |
|11| Epsilon Indi, | 5.2 | 87 ” |
|12| Œltzen, 17,415, | 9.0 | 94 ” |
|13| 1,516, Draco, | 7.0 | 101 ” |
|14| Omicron Eridani, | 4.4 | 101 ” |
|15| Altair, | 1.6 | 101 ” |
|16| Bradley, 3,077, | 5.5 | 101 ” |
|17| Eta Cassiopeiæ, | 3.6 | 118 ” |
|18| Vega, | 1.0 | 128 ” |
|19| Capella, | 1.2 | 174 ” |
|20| Arcturus, | 1.0 | 204 ” |
|21| Pole Star, | 2.1 | 215 ” |
|22| Mu Cassiopeiæ, | 5.2 | 320 ” |
|23| 1,830, Groombridge,| 6.5 | 426 ” |
+--+--------------------+----------+------------------+
This table presents the most trustworthy data which we have yet
obtained with reference to stellar distances. As a great number of
attempts have been made on stars which, by their brightness or by the
magnitude of their proper motion, would appear to be the nearest to us,
we may believe that the star now considered as the nearest is really
so, and that there is no other less distant. Thus our sun, a star
in the immensity, is isolated in infinitude, and _the nearest_ sun
reigns at twenty-five trillions of miles from our terrestrial abode.
Notwithstanding its unimaginable velocity of 186,400 miles a second,
light moves, flies, during four years and one hundred and twenty-eight
days to come from this sun to us. Sound would take more than three
millions of years to cross the same abyss. At the constant velocity of
thirty-seven miles an hour, _an express train starting from the sun
Alpha Centauri would not arrive here till after an uninterrupted course
of nearly seventy-five millions of years_.
Here, then, are the nearest suns to us. These stars, twenty-three
in number, are almost the only ones which have shown a perceptible
parallax; still the result is very doubtful for the last four, of which
the parallax is less than a tenth of a second. Attempts have been made
to ascertain the parallax of all the stars of the first magnitude,
and the result has been negative for those which are not entered in
this list. Canopus, Rigel, Betelgeuse, Achernar, Alpha of the Cross,
Antares, Spica, and Fomalhaut, do not show a perceptible parallax. The
fine star Alpha Cygni, which shines near 61 Cygni, does not present to
the most accurate researches any trace of fluctuation: it is, then,
incomparably more distant than its modest neighbor--at least five
times, and perhaps twenty times, fifty times, one hundred times beyond
that. What must be the colossal size and amazing light of these suns,
of which the distance is greater than three hundred to four hundred
trillions of miles, and which nevertheless still shine with so splendid
a brightness!
We did not know the distance of any stars till the year 1840. This
shows how recent this discovery is; indeed, we have hardly now begun
to form an approximate idea of the real distances which separate the
stars from each other. The parallax of 61 Cygni, the first which was
known, was determined by Bessel, and resulted from observations made at
Königsberg from 1837 to 1840. Since then, the first figure obtained has
been corrected by a series of more recent observations.
Such distances are amazing and almost terrifying to the imagination.
The mind is bewildered and almost overwhelmed when attempting to form a
conception of such portions of immensity, and feels its own littleness,
the limited nature of its powers, and its utter incapacity for grasping
the amplitudes of creation. But though it were possible for us to wing
our flight to such a distant orb as 61 Cygni, we should still find
ourselves standing only on the verge of the starry firmament where ten
thousands of other orbs a thousand times more distant would meet our
view. We have reason to believe that a space equal to that which we are
now considering intervenes between most of the stars which diversify
our nocturnal sky. The stars appear of different magnitudes; but we
have the strongest reason to conclude that in the majority of instances
this is owing, not to the difference of their real magnitudes, but to
the different distances at which they are placed from our globe.
If, then, the distance of a star of the first or second magnitude, or
those which are nearest to us, be so immensely great, what must be the
distance of stars of the sixteenth or twentieth magnitude, which can
be distinguished only by the most powerful telescopes? Some of these
must be many millions of times more distant than the nearest star whose
distance now appears to be determined. And what shall we think of the
distance of those which lie beyond the reach of any telescope that has
yet been constructed, stretching beyond the utmost limits of mortal
vision, within the unexplored regions of immensity? Here even the most
vigorous imagination drops its wing, and owns itself utterly unable to
penetrate this mysterious and boundless unknown.
Turning now from the sun, whose distance was first measured, and from
the nearest star with which we are acquainted, let us think about the
most radiant star in the heavens--Sirius, “the blazing Dog-star of the
ancients;” named by one astronomer “the king of suns.”
First, as to the color of Sirius. He belongs to the order of “White
Suns,” and among all the white suns known to us, Sirius ranks as
chief. There may be many at greater distances far surpassing him in
size, and weight, and brilliancy; but we can only speak so far as we
know. Strange to say, Sirius was not always a “white sun;” for ancient
writers describe him as being, in their days, a _red_ star. This change
is very singular, and difficult to understand. But Sirius is not the
only example of the kind. Many alterations in color have been noticed
as taking place, often in a much shorter space of time. For instance,
one star, which was a white sun in the days of Herschel, is now a
golden sun.
Secondly, as to the distance of Sirius. Like a few other stars, Sirius
lies not quite so far away as to be beyond reach of measurement.
No base-line upon earth would cause the slightest seeming change of
position in him; but as our earth journeys round the sun, the line from
one side of her orbit to the other is found wide enough. A base-line
of one hundred and eighty-six millions of miles does cause just a tiny
seeming change.
It is very little even with Alpha Centauri, and with Sirius it is much
less. The “displacement” of Sirius is so slight that to measure his
distance with exactness is impossible. Sirius lies more than twice as
far away from earth as Alpha Centauri. To reach Sirius, the straight
line between earth and sun must be repeated six hundred and twenty-six
thousand times. Light, which reaches us from the sun in eight minutes
and a half, and from Alpha Centauri in four years and a third, can not
reach us from Sirius in less than nine years.
Thirdly, as to the size of Sirius. Here, of course, we are in
difficulties. Radiantly as Sirius shines on a clear night, and dazzling
as he looks through a powerful telescope, he shows no real disk or
round surface, but only appears as one point of brilliant light.
Some believe him to be much the same size as our sun, while others
believe him to be very much larger. But we have no certain ground to
rest upon. The only safe method of calculating the probable size--or,
rather, weight--of a star is through the discovery of a companion,
and a knowledge of its distance from the chief star, and its time of
revolution round the chief star.
Fourthly, as to the motions of Sirius--not his nightly apparent
movement, caused by the earth’s turning on her axis, but his real
journey through space. For a long while it was only possible to observe
the movements of a star when the star was traveling _sideways_ to us
across the sky. A star coming straight towards us, or going straight
away from us, would seem to be at rest. Lately, however, by means
of that remarkable instrument, the spectroscope, it has been found
possible to measure the motions of stars coming towards or going away
from us. This is possible as yet only in a few scattered cases, but
among those few is the brilliant Sirius.
The sideways motion of Sirius had been known before. It now appears
that he does not move exactly sideways to us, but is rushing away in a
slanting direction at the rate of thirty miles each second, or about
one thousand millions of miles a year.
How many millions upon millions of miles Sirius must now be farther
from us than in the days of the ancients! Yet he shines still, the most
brilliant star in the sky. So small a matter are all those millions of
miles, compared with the whole of his vast distance from us, that we do
not perceive any lessening of light.
It is an interesting fact that while Sirius is moving away from us,
we are also moving away from him. Our “first station ahead,” in the
constellation Hercules, lies exactly in the opposite direction from
Sirius. But the sun does not move so fast as Sirius. He is believed
to accomplish only about one hundred and fifty millions of miles each
year, drawing all his planets with him.
Fifthly, has Sirius a family, or system, like that of our sun?
Why not? Common sense and reason alike answer with a “Probably,
yes”--not only about Sirius, but about other stars also. No doubt
the systems--the number, size, weight, speed, distance, and kind of
planets--differ very greatly. No doubt there are boundless varieties of
beauty and grandeur.
But that our sun should be the head of so wonderful and complex a
system, that his rays should be the source of life and heat to so many
dependents, and that all the myriads of suns besides should be mere
solitary lamps shining into empty space, warming, lighting, controlling
_nothing_, is an idea scarcely to be looked in the face.
Of course, there may be other and different uses for some of these
suns, beyond our understanding. We must not be positive in the matter.
It seems, however, pretty certain that Sirius at least is not a
solitary, unattended sun.
Astronomers, carefully watching his movements, were somewhat perplexed.
As with Uranus, the attraction of a heavy body beyond was suspected
from the nature of the planet’s motions, so it happened again with the
far more distant Sirius. Astronomers could only explain his movements
by supposing the attraction of some large and near satellite. No one
knew anything about such a satellite, but it was felt that one must
exist.
Nearly twenty years had elapsed after Bessel had predicted the
disturber of Sirius before the telescopic discovery which confirmed it
was made. The circumstances under which that discovery was made are
not, indeed, so dramatic as those which attended the discovery of
Neptune, but yet they have an interest of their own. In February, 1862,
Alvan Clark & Sons, the celebrated telescope-makers, of Cambridge,
Massachusetts, were completing a superb eighteen-inch object-glass for
the Chicago Observatory. Turning the instrument on Sirius, for the
purpose of trying it, the practiced eye of Alvan Graham Clark, the
son, soon detected something unusual, and he exclaimed, “Why, father,
the star has a companion!” The father looked, and there was a faint
companion due east from the bright star, and distant about ten seconds
of a degree. This was exactly the predicted direction of the companion
of Sirius, and yet the observers knew nothing of the prediction. As
the news of this discovery spread, many great telescopes were pointed
on Sirius; and it was found that when observers knew exactly where to
look for the object, many instruments would show it. The new companion
star to Sirius lay in the true direction, and it was now watched with
the keenest interest, to see whether it also was moving in the way
it should move,--if it were really the body whose existence had been
foretold. Four years of observation showed that this was the case, so
that hardly any doubt could remain that the telescopic discovery had
been made of the star which had caused the inequality in the motion of
Sirius.
It is certainly a very remarkable fact that, out of the thousands of
stars with which the heavens are adorned, no single star has yet been
found which certainly shows an appreciable disk in the telescope. We
are aware that some skillful observers have thought that certain small
stars do show disks; but we may lay this aside, and appeal only to the
ordinary fact that our best telescopes turned on the brightest stars
show merely glittering points of light, so hopelessly small as to elude
our most delicate micrometers. The ideal astronomical telescope is,
indeed, one which will show Sirius, or any other bright star, as nearly
identical as possible with Euclid’s definition of a point, being that
which has no parts and no magnitude.
Lastly, what is Sirius made of? The late discovery of spectrum
analysis, or of the instrument called the spectroscope, helps us here.
A little further explanation on this subject will be given later. It
may be observed in passing that before the said discovery, astronomers
can scarcely be asserted to have known with any certainty that stars
were suns. They could, indeed, be sure that at the vast distances of
the fixed stars no bodies, shining by merely reflected light, could
possibly be visible to us. But there knowledge stopped.
Now we can say more. Now the spectroscope, by breaking up and dividing
for us the slender ray of light traveling from each star, has shown to
us something of the nature of the stars. Now we know that the stars,
like our sun, are burning bodies, surrounded by atmospheres full of
burning gas.
It has even been found out that in Sirius there are large quantities of
sodium and magnesium, besides other metals, and an abundant supply of
hydrogen gas.