Speaker 1: Section twenty six of Sun, Moon and Stars Astronomy for Beginners.
Speaker 1: This is a LibriVox recording. All LibriVox recordings are in
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Speaker 1: and Stars Astronomy for Beginners by Agnes Gibern. The Milky Way,
Speaker 1: who knoweth not in all these that the hand of
Speaker 1: the Lord hath wrought this job twelve, line nine. One
Speaker 1: star differeth from another star In Glory Corinthians fifteen, line
Speaker 1: forty one. The Milky Way forms a soft band of
Speaker 1: light round the whole heavens. In the southern hemisphere, as
Speaker 1: in the northern hemisphere, it is to be seen. In
Speaker 1: some parts the band narrows, in some parts it widens.
Speaker 1: Here it divides into two branches. There we find dark
Speaker 1: spaces in its mists. One such space in the south
Speaker 1: is to the naked eyes, so black and almost starless
Speaker 1: as to have been named the coal Sack. But photography
Speaker 1: shows abundance of stars to lie there. Also, all along
Speaker 1: over the background of soft dim light lies a scattering
Speaker 1: of brighter stars shining on its surface. Much interest and
Speaker 1: curiosity have long been felt about this mysterious milky Way.
Speaker 1: That it consists of innumerable suns, and that our sun
Speaker 1: is one among them has been believed for a considerable time.
Speaker 1: But other questions arise. How many stars does the Milky
Speaker 1: Way contain? What is its shape? How far does it reach?
Speaker 1: No harm in asking the questions only we have to
Speaker 1: be satisfied in astronomy. To ask many questions which cannot
Speaker 1: yet receive answers. No harm for man to learn that
Speaker 1: the utmost reach of his intellect must fall short in
Speaker 1: any attempt to sound the depths of the universe, even
Speaker 1: as the arm of a child would fall short in
Speaker 1: seeking to sound the depths of the ocean over the
Speaker 1: side of a little boat. For attempts had been made
Speaker 1: to sound the depths of our star galaxy out of
Speaker 1: this little earth boat. The idea first occurred to the
Speaker 1: great Herschell, and a grand idea, it was only a
Speaker 1: hopeless one. He turned his powerful telescope north south east west.
Speaker 1: He counted the stars visible at one time in this
Speaker 1: in that in the other directions he found a marked
Speaker 1: difference in the numbers. The portions of sky seen through
Speaker 1: his telescope was about one quarter the size of that
Speaker 1: covered by the moon. Sometimes he could merely perceive two
Speaker 1: or three bright points on a black background. At other
Speaker 1: times the field of his his telescope was crowded. In
Speaker 1: the fuller portions of the Milky Way, he had four
Speaker 1: or five hundred stars under view at once. In one place,
Speaker 1: he saw about one hundred and sixteen thousand stars pass
Speaker 1: before him in a single quarter of an hour. Herschel
Speaker 1: took it for granted that the stars of the Milky Way,
Speaker 1: uncountable in numbers, are as a rule, much the same
Speaker 1: in size. So the brightest stars would as a rule
Speaker 1: be nearest, and dimmest stars would, as a rule be
Speaker 1: furthest off where he found stars clustering thickly beyond his
Speaker 1: power to penetrate, he believed that the Milky Way reached
Speaker 1: very far in that direction, where he found black space
Speaker 1: unlighted by stars or lighted by few stars. He decided
Speaker 1: that he had found the borders of our galaxy in
Speaker 1: that direction. Following these rules which he had laid down,
Speaker 1: he made a sort of rough sketch of what he
Speaker 1: sow posed might be the shape of the Milky Way.
Speaker 1: He thought it was somewhat flat, extending to a good
Speaker 1: distance breadth wise and a much greater distance lengthwise, and
Speaker 1: he placed our Sun not far from the middle. This
Speaker 1: imagined shape of the Milky Way is called the cloven
Speaker 1: disk theory. To explain the appearance of the Milky Way
Speaker 1: in the sky, Herschel supposed it to be a cloven
Speaker 1: or split through half of its length, with a black
Speaker 1: space between the two split parts. It seems that Herschel
Speaker 1: did not hold strongly to this idea in later years,
Speaker 1: and the rules on which he formed it no longer
Speaker 1: hold good. For how do we know that the stars
Speaker 1: of the Milky Way are as a rule much the
Speaker 1: same in size? Certainly the planets of the Solar System
Speaker 1: are very far from being uniform, and the few stars
Speaker 1: whose weight can with any certainty be measured seem to
Speaker 1: vary considerably. There is a great difference also between the
Speaker 1: large and small suns in many of the double stars. Again,
Speaker 1: although bright stars undoubtedly are as a rule, the nearest
Speaker 1: and dim stars furthest off, there are many exceptions. Look
Speaker 1: at Sirius and sixteen one Signy Sirious, the most radiant
Speaker 1: star in the heavens, and sixty one Signey almost invisible
Speaker 1: to the naked eye. According to this rule, sixteen one
Speaker 1: Signey ought to lie at an enormous distance beyond Sirius.
Speaker 1: Yet in actual fact serious is the further away of
Speaker 1: the two. For ought we know there may be many
Speaker 1: small telescopic stars, much nearer to us than many of
Speaker 1: the brighter stars, which we can plainly see with the
Speaker 1: naked eye, and only invisible without the help of the
Speaker 1: telescope because of their smallness, not so much because of
Speaker 1: their distance. This line of reasoning shows how we easily
Speaker 1: mistakes may have been made in a matter of no
Speaker 1: slight importance. Some chapters back, I spoke of the light
Speaker 1: traveling to us from far distant stars, stars so distant
Speaker 1: that their light must have taken thousands of years to
Speaker 1: reach us. Only there is no must we do not
Speaker 1: actually know the fact. A writer says, the illustrious Herschel
Speaker 1: penetrated on one occasion into this spot, the star cluster
Speaker 1: of the sword hand in the constellation of Perseus, until
Speaker 1: he found himself among the depths, whose light could not
Speaker 1: have reached him in less than four thousand years. So
Speaker 1: Herschel believed, But he did not know. There is no
Speaker 1: certain could not in the matter. The distance of those
Speaker 1: stars had not and has not been mathematically measured. Herschel
Speaker 1: judge of it by their dimness, by the strong power
Speaker 1: needed to make them visible, and by the rules which
Speaker 1: he had adopted as most likely true. This was no
Speaker 1: sure mode of judging. The stars might be as far
Speaker 1: distanced as he is supposed. On the other hand, they
Speaker 1: might be very much nearer, if too far for our
Speaker 1: measuring line to reach them. They may be only just
Speaker 1: too far, and their seeming smallness and dimness, instead of
Speaker 1: being caused by vast reaches of space between, may simply
Speaker 1: be caused by actual smallness or actual dimness. There are
Speaker 1: little suns as well as great suns in the Milky Way.
Speaker 1: It is possible that hundreds of little suns may exist
Speaker 1: for every single specimen of a great sun. Again, when
Speaker 1: Herschel found black spaces in the heavens almost void of stars,
Speaker 1: and believed that he had reached the outside borders of
Speaker 1: the Milky Way, he might be right, or he might
Speaker 1: be mistaken. The limit might lie there, or thousands more
Speaker 1: of small stars might extend in that very direction, too
Speaker 1: far off for their little glimmer to be seen through
Speaker 1: the most powerful telescope. A good deal of attention has
Speaker 1: been paid to the arrangement of stars in the skies.
Speaker 1: The more the matter is looked into, the more it
Speaker 1: appears that stars are neither regular in size nor regular
Speaker 1: in distribution. It would seem that they are not flung
Speaker 1: broadcast through the heavens, each one alone and independent of
Speaker 1: the rest. They are placed, often, as they have already seen,
Speaker 1: in pairs, in triplets, in quartets, in clusters. Also, the
Speaker 1: great masses of them in the heavens seem to be
Speaker 1: more or less arranged in streams and sprays and spirals.
Speaker 1: It should, however, be understood, that what may look to
Speaker 1: us like streams or spirals may in reality be nothing
Speaker 1: of the kind. Distance is very deceptive. Even on Earth.
Speaker 1: Any object far off may appeared to be close to
Speaker 1: another object from which it is really separated by many miles.
Speaker 1: And if this is so on our little Earth, how
Speaker 1: much more easily may one be mistaken in celestial landscapes.
Speaker 1: We must now try to form a few clear ideas
Speaker 1: about the richer and poorer parts of the heavens as
Speaker 1: viewed from Earth. In considering stars of the first six magnitudes,
Speaker 1: only stars visible to the naked eye. A somewhat larger
Speaker 1: number is found in the southern hemisphere than in the
Speaker 1: northern hemisphere. In both hemispheres there are regions densely crowded
Speaker 1: with stars in regions, by comparison, almost empty. It has
Speaker 1: been long question whether the number of bright stars is
Speaker 1: or is not greater in the Milky Way than in
Speaker 1: other parts of the sky. Careful calculations have at length
Speaker 1: been made. It appears that the whole of the Milky Way,
Speaker 1: that zone of soft light passing round the Earth covers.
Speaker 1: If we leave out the coal sat and other such
Speaker 1: gaps between one tenth and one eleventh of the whole heavens,
Speaker 1: the entire number of naked eye stars or stars of
Speaker 1: the first six magnitudes does not exceed six thousand, and
Speaker 1: of these, eleven hundred and fifteen lie scattered along the
Speaker 1: bed of the Milky Way stream. If the brighter stars
Speaker 1: were scattered all over the sky as thickly as throughout
Speaker 1: the Milky Way, their number would amount to twelve thousand
Speaker 1: instead of only six thousand. This shows us that the
Speaker 1: higher magnitude stars really are collected along the Milky Way
Speaker 1: in greater numbers than elsewhere in the dark spaces of
Speaker 1: the Milky Way. On the contrary, bright stars are so
Speaker 1: few that, if they were scattered in the same manner
Speaker 1: over all the sky, their present number of six thousand
Speaker 1: would come down to twelve hundred and forty, which would
Speaker 1: be a serious loss. No rest, no quiet, no repose
Speaker 1: in that great universe, which to our dim eyesight looks
Speaker 1: so fixed and still, but one perpetual rush of moving
Speaker 1: suns and worlds. For every star has its own particular motion,
Speaker 1: every sun is pressing forward in its own appointed path.
Speaker 1: And among the myriads of stars, bright blazing spheres of
Speaker 1: white or golden, red, blue, or green radiance, sweeping with
Speaker 1: steady rush through space, our Sun also hastens onward. When
Speaker 1: I speak of the Sun's movement, it must of course
Speaker 1: be understood that the Earth and planets all travel with him,
Speaker 1: much as a great steamer on the sea might drag
Speaker 1: in his wake a number of little boats. From one
Speaker 1: of the little boats, you could judge of the steamer's
Speaker 1: motion quite as well as if you were on the
Speaker 1: steamer itself. Astronomers judge partly of the Sun's motion by
Speaker 1: watching the seeming backward drift of stars to the right
Speaker 1: and left of him, and the watching can be as
Speaker 1: well accomplished from Earth as from the Sun himself. After all,
Speaker 1: this mode of judging is and must be very uncertain.
Speaker 1: Among the millions of stars visible, we know the distances
Speaker 1: roughly of less than one hundred, and every star has
Speaker 1: its own real motion, which has to be separated from
Speaker 1: the apparent change of position caused by the Sun's advance.
Speaker 1: It seems now probable that the Sun's course is directed
Speaker 1: more or less towards the neighborhood of the constellation Hercules.
Speaker 1: But if orbits of suns, like orbits of planets, are eclipses,
Speaker 1: he will curve away sideways long before he reaches Hercules.
Speaker 1: Another investigation gives a neighborhood of sixty one Signae as
Speaker 1: our next station. It is difficult to give any clear
Speaker 1: idea of the immensity of the universe, even of that
Speaker 1: portion of the universe which lies within reach of our
Speaker 1: most powerful telescopes. How far beyond such limits it may reach,
Speaker 1: we lose ourselves in imagining. Earlier in the book, we
Speaker 1: have supposed possible models of the Solar system, bringing down
Speaker 1: Sun and worlds to a small size, Yet keeping due proportions.
Speaker 1: What if we were to attempt to make a reduced
Speaker 1: model of the universe, that is, of just so much
Speaker 1: of it as comes within our ken. Suppose a man
Speaker 1: were to set himself to form such a model, including
Speaker 1: every star which has ever been seen. Let him have
Speaker 1: one tiny ball for the Sun, in another tiny ball
Speaker 1: for Alpha Centauri, and let him, as a beginning, set
Speaker 1: the two one yard apart. That single yard represents ninety
Speaker 1: one millions of miles two hundred and thirty thousand times repeated.
Speaker 1: Then let him arrange countless multitudes of other tiny balls
Speaker 1: at due distances, some five times, ten times, twenty times
Speaker 1: fifty times as far away from the Sun as Alpha Centauri.
Speaker 1: It is said that the known universe made upon a
Speaker 1: model of these proportions would be many miles in length
Speaker 1: and breadth, but the model would appear fixed as marble.
Speaker 1: The sizes and distances of the stars being so enormously reduced,
Speaker 1: their rates of motion would be lessened in proportion. Long
Speaker 1: intervals of time would need to pass before the faintest
Speaker 1: motion of one of the millions of tiny balls could
Speaker 1: become visible to the human eye. End of Section twenty
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