regularly distributed; nevertheless, look at that whitish, undecided,
vapory glimmer which girdles the heavens as with a belt. It is the
Milky Way.[1] As we approach the borders of this star-cloud in our
inspection, the stars appear more and more crowded together, and
most of them so small that the eye can scarcely distinguish them.
The accumulation of stars in the direction of the Milky Way is more
especially visible when we examine the heavens with the aid of a
powerful telescope.
The Milky Way itself is nothing more than an immensely extended zone
of stars, that is, of suns, since each star, from the most brilliant
to the faintest, is a sun.
Here, then, is an immense group, a gigantic assemblage of worlds,
which seems to embrace all the universe, if it be true that the
greater number of the scattered stars situated out of the Milky Way
nevertheless form part of it. In reality, this multitude of millions
of suns is divided into numerous and distinct groups, and those into
others still more restricted in number, each composed of two or three
suns.
What breadth of space does each of these groups occupy? What is
the measure of the space which holds them all? The most powerful
imagination in vain attempts to answer these questions intelligibly;
here numbers fail us.
Let us add—a fact well proved, and one which will seem strange to
many—
Our sun himself is a star of the Milky Way.
In examining attentively every part of the starry vault, a keen eye
perceives here and there whitish spots resembling little clouds. One
would say they were so many patches detached from the Milky Way, from
which, however, they are often very distinct and very distant. The
telescope discovers by thousands those cloud-patches, these—to give
them their astronomical name—_Nebulæ_.
It was formerly imagined that each of these star-clouds was nothing
more than an accumulation of stars, very close together, and very
numerous—so many Milky Ways lying outside our own, and for the most
part so distant that the most powerful instruments were able only
to distinguish a confused glimmering. One of the most important
observations of modern times, however, has shown that many of
these nebulæ, including the most glorious one in our northern
hemisphere—that in the sword-handle of Orion—are but masses of
glowing gases.
Others, again, of these cloud-like masses—cloud-like by reason of
their distance—show us, faintly shining on a background of apparent
nebulæ, brilliant stars, larger no doubt, or more brilliant, than
their fellows, and some of these objects called “Star-Clusters,”
which are nearest to us, are among the most glorious objects revealed
to us by our telescopes.
Let us attempt now to conceive what fearful distances separate these
archipelagoes of worlds from our own!
Unfathomable abysses whose unspeakable depths the most powerful
telescopes increase indefinitely! Profound, endless, bottomless, but
lighted up by millions of suns!
Such appears to us the universe from the natural observatory where we
are placed. But to obtain a more complete idea of its constitution,
of the infinite variety of its members, we must descend from those
regions, where the sight and mind are lost, to a group, nearer to
us, and therefore more accessible to the investigations of man—to
that group, or system, of which the earth forms part.
Of this the sun is the centre.
Round this focus of light and heat, but at various distances, revolve
more than a hundred secondary bodies—Planets, some of which are
accompanied by smaller ones—Satellites. Not self-luminous, they
would be invisible to us, if the light, which they receive from the
sun, were not reflected toward the earth, making them also appear
as luminous points spread over the celestial vault like so many
stars. Such would be the appearance of the earth seen in space, at a
distance sufficiently great.
A common character distinguishes all the celestial bodies that form
part of this group—the Solar System—from the multitude of other
stars. For while the suns, composing what is called the Sidereal
Universe, are situated at distances seemingly infinite, the bodies
composing the group of which we speak are relatively much nearer the
earth, are, in fact, our neighbors.
What results from this double fact? Two very simple consequences,
easily understood.
The first is, that the stars do not undergo any sensible change
of position in the starry vault. Their distance is such that they
appear actually at rest in the depths of space; hence the term _Fixed
Stars_—now abandoned, because a minute and elaborate study of their
relative positions has established the fact that the stars really do
move in the remote regions of the heavens. The apparent immobility
of which we have spoken, and which is one of their characteristics,
is evidenced by the uniformity of appearance preserved for
centuries by the artificial groups of stars, to which the name of
Constellations has been given.
Now, it is otherwise with the bodies that revolve round our sun: they
are near enough to the earth to allow of their displacements in space
being perceived in short intervals of time. Traveling, by virtue of
their proper motions along the starry vault, distances which appear
greater as their own distance from us is less, these bodies received
at the outset the name they have since retained—_Planets_, or
Wandering Stars.
It is thus that, when we stand in the middle of an extensive plain,
we judge distant objects—those that border the horizon—to be
immovable; while we instantly perceive the slightest change of place
in the near ones. It is true that when we ourselves move, the real
movements become complicated with the apparent movements, but the
former must be distinguished, if we wish to have an exact idea of the
actual course traveled. This complication of the apparent movements
of the planets—a necessary consequence of the movement of the
earth—is one of the most striking testimonials to the reality of the
latter; but it must also be added, that this was precisely the stone
of stumbling of ancient astronomy until the time—and that not long
ago—when the real movements were made known. Movements of rotation,
movements of revolution, around the common centre, the duration of
these movements, distances, forms and dimensions, distribution of
light and heat, all change in passing from one planet to another. And
yet, marvelous thing, the same laws govern, all in such a way that
the unity of plan is not less marked than the astonishing variety of
the phenomena.
One circumstance common to all the bodies of the solar system
forcibly strikes the imagination. It is, that these enormous
masses—these globes, many of which are much heavier than the earth,
and lastly, the earth itself—are not only suspended in space, but
move through the ether with velocities truly stupendous.
Imagine yourself a spectator, standing immovable in space. A luminous
body appears in the distance, little by little you see it approach
and increase in size; its immense circumference, which exceeds a
hundred thousand leagues, is in rapid rotation, which makes each
point on its periphery travel through nine miles a second. The globe
itself passes before you, carried through space with a velocity
twenty-four times greater than that of a cannon-ball. In such a way
Jupiter would appear to you traveling in its orbit. This headlong
course would banish it forever to the most remote regions of the
visible universe, if it were not subdued and held by the powerful
attraction of a globe a thousand times larger than its own—by the
sun himself. Not only does astronomy show, by undeniable proofs, the
reality of these marvelous movements—not only has she arrived at the
knowledge of their invariable constancy, at least during thousands of
centuries; but she has found in their very rapidity the cause of the
stability of all the celestial bodies.
If there is difficulty in imagining such masses freely circulating in
the ether, how much more are we impressed when we consider that these
rapid movements are not confined to the planets; and when we look
upon the sun with all his retinue as moving in an orbit yet unknown,
himself attracted no doubt by a more powerful sun, or by a group
of suns! All the stars which by reason of their infinite distances
appear immovable, move in different directions; and we shall see
later, that if these movements are performed with extreme slowness,
the slowness is apparent only. In reality, these are the most rapid
celestial movements that we know of.
Thousands of centuries will be necessary before these immense
sidereal voyages are accomplished. Their vast periods are to the
length of our year what the dimensions of the earth are to the
distances of the stars; and, according to the happy expression of
Humboldt, they make of the universe an eternal timekeeper. Thus,
in the contemplation of celestial phenomena, the idea of infinite
duration impresses itself on the mind with the same irresistible
power as the idea of the infinity of space.
FOOTNOTES:
[1] Via Lactea. It is also called the Galaxy, from the Greek word for
the same thing.
SPACE.—RICHARD A. PROCTOR
Although astronomy tells us in the clearest words of the vast depths
of space which surround our earth on all sides, we are not thereby
enabled to realize their enormous extension. It is not merely that
the unknown depths beyond the range of our most powerful telescopes
are inconceivable, but that the parts of space which we can examine
are on too large a scale for us to conceive their real dimensions. It
is hardly going too far to say that our powers of actual conception
are limited to the extent of space over which the eye _seems_ to
range in the daytime. Of course, in the daytime, at least in clear
weather, there is one direction in which the eyesight ranges over a
distance of many millions of miles—namely, where we see the sun. But
the sense of sight is not cognizant of that enormous distance, and
simply presents the sun to us as a bright disk in the sky, or perhaps
rather nearer to us than the sky. Even the distance of the sky itself
is underestimated. A portion of the light we receive from the sky
on a clear day comes from parts of the atmosphere distant more than
thirty or forty miles from us; but the eye does not recognize the
fact. The blue sky seems a little further off than the clouds, but
not much; the light clouds of summer seem a little, but not much,
further off than the heavier clouds of a winter sky; a cloud-covered
winter sky seems a little further off than heavy rain-clouds. The
actual varieties of distance among clouds of various kinds are not
much more clearly discerned than the actual varieties of distance
among the heavenly bodies. The estimate formed of the distance of a
cloud-covered sky overhead probably amounts to little more than a
mile, and it is very doubtful whether the mind presents the remotest
depths of a blue sky overhead at more than two miles. Toward the
horizon the distance seems greater, and probably on a cloudy day
the sky near the horizon is unconsciously regarded as at a distance
of about five miles, while blue sky near the horizon may be regarded
as lying at a distance of six or seven miles, the arch of a blue sky
seeming to be far more deeply curved than that of a cloud-covered sky.
It is to distances such as these that the mind unconsciously refers
the celestial bodies. We know that the moon is about 2,000 miles in
diameter, but the mind refuses to present her to us as other than
a round disk much smaller than those other objects in sight which
occupy a much larger portion of the field of vision. The sun can not
be conceived to exceed the moon enormously in size, seeing that he
appears no larger; and all the multitude of stars are judged by the
sight to be mere bright points of light in reality as they appear to
be.
How, then, can we hope to appreciate the vastness of space whereof
astronomy tells us? To the student of science attempting to conceive
the immensities of whose existence he is assured, the same lesson
might be taught in parable which the child of St. Augustine’s vision
taught the Numidian theologian. As reasonably might an infant hope to
pour the waters of ocean into a hollow, scooped with his tiny fingers
in the sand, as man to picture in his narrow mind the length and
breadth and depth of the abysses of space in which our earth is lost.
Yet, as a picture of a great mansion may be so drawn on a small scrap
of paper as to convey just ideas of its proportions, so may the great
truths which astronomy has taught us about the depths of space be so
presented that just conceptions may be formed of the proportions of
at least those parts of the universe which lie within the range of
scientific vision, though it would be hopeless to attempt to conceive
their real dimensions.
When we learn that a globe as large as our earth, suspended beside
the moon, would seem to have a diameter exceeding hers nearly four
times, so that the globe would cover a space in the heavens about
thirteen times as large as the moon covers, we form a just conception
of the size of the moon as compared with the earth, though the mind
can not conceive such a body as the moon or the earth really is.
When, in turn, we are told that if a globe as large as the earth, but
glowing as brightly as the sun, were set beside the sun, it would
look a mere point of light, we not only learn to picture rightly
to ourselves how largely the sun exceeds the earth, but also how
enormous must be the real distance of the sun.
Another step leads us to a standpoint whence we can form a correct
estimate of the vast distance of the fixed stars; for we can learn
that so enormous is the distance of even the nearest fixed star,
that the tremendous space separating the earth from that star sinks
in turn into the merest point, insomuch that if a globe as bright as
the sun had the earth’s orbit as a close-fitting girdle, then this
glorious orb (with a diameter of some 184,000,000 of miles) would
look very much smaller than such a globe as our earth would look at
the sun’s distance—would, in fact, occupy but about one-fortieth
part of the space in the sky which she, though she would then look a
mere point, would occupy if viewed from that distance.
But there is a way of viewing the immensities of space which, though
not aiding us indeed to conceive them, enables the mind to picture
their proportions better than any other. The dimensions of the
earth’s path around the sun sink into insignificance beside those
of the outermost planets; but these in their turn dwindle into
nothingness beside those of some among the comets. From the path of
these comets, if only sentient and reasoning beings could trace out
in a comet’s company those mighty orbits, and could have for the
duration of their existence not the brief span of time which measures
the longest human life, but many circuits of their comet home around
the same ruling orb (as we live during many circuits of our globe
around the sun), the dimensions of the star-depths, which even to
scientific insight are all but immeasurable, would be directly
discernible. Not only would the proportions of that mighty system be
perceived, whose fruits and blossoms are suns and worlds, but even
the gradually changing arrangement of its parts could be discerned.
Some comets, indeed, do not travel around the sun, but flit from
sun to sun on journeys lasting millions of years, paying each sun
but a single visit. A being inhabiting such a comet, and having
these interstellar journeys as the years of his existence, so that
he could live through many of them, would have a wonderful insight
into the economy of the stellar system. If his powers of conception
as far exceeded ours as the range of his travels and the duration
of his existence, he would be able to recognize the proportions of
a large part of the stellar universe as clearly as we recognize the
proportions of the solar system.
But leaving these wonderful wanderers, whose journeys are as far
beyond our powers of conception as the immensity of the regions
of star-strewn space, we may find, among the comets belonging to
the sun’s domain, bodies whose range of travel would give their
inhabitants far clearer views of the architecture of the heavens than
even the profoundest terrestrial astronomer can possibly obtain.
Such a comet as Halley’s, for instance, though one of comparatively
limited range in space, yet travels so far from the sun that, from
the extreme part of its path, it sees the stars displaced nearly
twenty times as much (owing to its own change of position) as they
are from the earth on opposite sides of her comparatively narrow
orbit. And the length of this comet’s year, if it indicated the lives
of all creatures traveling along with it, would suggest a power of
patiently watching the progress of changes lasting not a few of our
years only, but for centuries. Seventy-five or seventy-six years
elapse between each return of this comet to the sun’s neighborhood,
and one who should have lived during sixty or seventy circuits of
this body around its mighty orbit would have been able to watch the
rush of stars, with their velocities of many miles per second, until
visible displacements had taken place in their positions.
This, however, is as nothing compared with the mighty range in space
and the enormous period of the orbit of the great comet of the year
1811. This comet is, on the whole, the most remarkable ever known.
It was visible for nearly seventeen months, and though it did not
approach the sun within 100,000,000 miles, and was therefore not
subject to that violence of action which has caused enormous tails to
be thrown out from comets which have come within a few million miles
of him, or even within less than a quarter of his own diameter, it
flourished forth a tail 120,000,000 of miles in length. Its orbit
has, according to the calculations of the astronomer Argelander, a
space exceeding the earth’s distance from the sun 211 times, and thus
surpassing even the mighty distance of Neptune fully seven times.
It occupies in circuiting this mighty path no less than 3,065 of
our years (with a possible error either way of about forty-three
years). So that, according to Bible chronology, this comet’s last
appearance probably occurred during the rule of the Judge Tola,
son of Puah, son of Dodo, over the children of Israel, though it
may have occurred during the rule of his predecessor Abimelech, or
during that of his successor Jair.[2] During one-half of the enormous
interval between that time and 1811 the comet was rushing outward
into space, reaching the remotest part of its path somewhere about
the year 278 (A. D.), and from that time to 1811 it was on its
return journey. It is strange to think, however, that though the
remotest part of its path lay 211 times further from the sun than
the earth’s orbit, yet even this mighty path, requiring more than
3,000 years for a single circuit, can not be said to have carried the
comet into the star-depths. If the earth were to shift its position
by the some enormous amount, the nearest fixed star would have
its apparent position changed only by about an eighth part of the
apparent diameter of the sun or moon, or by about one-quarter of the
distance separating the middle star of the Bear’s tail from its close
companion.
But this fact of itself is most strikingly suggestive of the vast
distance of the stars. For consider what it means. Imagine the
middle star of the Bear’s tail to be the really nearest of all the
stars instead of lying probably twenty or thirty times further away.
Conceive a comet belonging to that sun after making its nearest
approach to it to travel away upon an orbit requiring 3,000 years
for each circuit. _Then_ (supposing that star equal to our sun in
mass) the comet, though rushing away from its sun with inconceivable
velocity during 1,500 years, would, at the end of that vast
period, seem to be no further away than one-fourth of the distance
separating the sun from its near companion. Look at the middle star
of the Bear’s tail on any clear night, and on its small satellite,
remembering this fact, and the awful immensity of the star-depths
are strongly impressed upon the mind. But the observer must not fail
to remember that the star really is many times more remote than we
have here for a moment supposed, and that such a comet’s range of
travel would be proportionately reduced. Moreover, many among the
stars are doubtless hundreds, even thousands, of times still further
away.
Let us turn lastly to the amazing comet of the year 1744. We find
that though it had the longest period of any which has ever been
assigned to a comet as the result of actual mathematical calculation,
yet its range in space would scarcely suffice to change the
position of the stars in such sort that the aspect of the familiar
constellations would be materially altered. Euler, the eminent
mathematician, calculated for this comet a period of 122,683 years,
which would correspond, I find, to a distance of recession equal to
2,469 times the distance of the earth from the sun, or about eighty
times the distance of Neptune. Yet this is but little more than
twelve times the greatest distance of the comet of 1811. Probably
the actual range of such an orbit from the middle star of the Bear’s
tail would be equal in appearance to the range described above on
the supposition that the star is no further from us than the nearest
known star (Alpha Centauri). That is, such a comet, if it could be
seen and watched during a period of about 122,000 years, would seem
to recede from the star to a distance equal to about one-fourth the
space separating it from its close companion, and then to return to
the point of nearest approach to its ruling sun.
Such are the immensities of star-strewn space! The journey of a comet
receding from the sun with inconceivable velocity during hundreds
of thousands of years carries it but so small a distance from him
compared with the distance of the nearest star as scarcely to change
the appearance of the celestial landscape; and yet the distances
separating the sun from the nearest of his fellow suns are but as
hairbreadths to leagues when compared with the proportions of the
scheme of suns to which he belongs. These distances, though so mighty
that by comparison with them the inconceivable dimensions of our
own earth sink into utter nothingness, do not bring us even to the
threshold of the outermost court of that region of space to which the
scrutiny of our telescopes extends. Yet the whole of that region is
but an atom in the infinity of space.
FOOTNOTES:
[2] It might be suggested that the appearance of this blazing comet
among the stars drove the more superstitious of the Israelites at
that time to the worship of star-gods, as we read how, during the
Judgeship of Jair, they “served Baalim and Ashtaroth, and the gods
of Syria and the gods of Moab, and the gods of the Philistines, and
forsook the Lord and served not Him.” To a people like the Jews, who
seem to have been in continual danger of returning to the Sabaistic
worship of their Chaldean ancestors, the appearance of a blazing
comet may have been a frequent occasion of backsliding.
EXTENT OF THE SIDEREAL HEAVENS.—SIR ROBERT S. BALL