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<v Speaker 1>Section twenty five of Sun, Moon and Stars Astronomy for Beginners.

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<v Speaker 1>This is a LibriVox recording. All LibriVox recordings are in

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<v Speaker 1>the public domain. For more information or to volunteer, please

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<v Speaker 1>visit LibriVox dot org. Read by Bill Welch Sun Moon

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<v Speaker 1>and Stars Astronomy for Beginners by Agnes Geeburn, Groups and

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<v Speaker 1>clusters of suns. He telleth the number of the stars.

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<v Speaker 1>He calleth them all by their names, Psalm one forty seven,

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<v Speaker 1>line four. We have been thinking a good deal about

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<v Speaker 1>single stars and double stars as seen from Earth. Now

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<v Speaker 1>we have to turn our attention to groups, clusters, masses

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<v Speaker 1>of stars in the far regions of space. Have you

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<v Speaker 1>ever noticed, on a winter night, when the sky was

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<v Speaker 1>clear and dotted with twinkling stars, a band of faintly

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<v Speaker 1>glimmering light stretching across the heavens from one horizon to

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<v Speaker 1>the other. The band is irregular in shape, sometimes broader,

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<v Speaker 1>sometimes narrower, Here more bright, there, more dim. If you

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<v Speaker 1>were in the southern hemisphere, you would see the same

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<v Speaker 1>soft belt of light passing all across the southern heavens.

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<v Speaker 1>This band or belt is called the milky Way. Sometimes

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<v Speaker 1>it is called the stellar system or the universe. Early

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<v Speaker 1>in this book, Mansion was made of the word universe

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<v Speaker 1>as used in two senses. The more modern use of

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<v Speaker 1>it for the Milky Way, or for the particular great

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<v Speaker 1>galaxy or gathering of stars to which our sun belongs

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<v Speaker 1>is the smaller meeting. But what is the Milky Way?

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<v Speaker 1>Is it made up of stars? So much we know

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<v Speaker 1>as the astronomer turns his telescope to the zone of

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<v Speaker 1>faintly gleaming light, he finds the stars appearing behind stars

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<v Speaker 1>in countless multitudes, and the stronger his telescope, the more

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<v Speaker 1>the white light changes into distant stars. Our sun we

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<v Speaker 1>believe to be one of the stars of the Milky Way,

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<v Speaker 1>merely one star among millions of stars, merely one golden

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<v Speaker 1>grain among the millions of sparkling gold dust grains scattered

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<v Speaker 1>lavishly through creation, scattered not recklessly, not by chance, but placed,

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<v Speaker 1>arranged and guided each by its maker's upholding hand. The

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<v Speaker 1>Milky Way, the galaxy, or the universe, as it has

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<v Speaker 1>been variously called, has great interest for astronomers. Many have

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<v Speaker 1>been the attempts made to discover its actual size, its

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<v Speaker 1>true shape, how many stars it contains, how far it extends.

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<v Speaker 1>But to all such questions the only safe answers to

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<v Speaker 1>be returned are fenced around with perhaps and maybe. There

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<v Speaker 1>are many very remarkable clusters of stars to be seen

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<v Speaker 1>in the heavens. Some few visible as faint spots of

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<v Speaker 1>light to the naked eye, though the greater number are

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<v Speaker 1>only to be seen through a telescope, either with the

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<v Speaker 1>naked eye or in the telescopes of varying power. They

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<v Speaker 1>show first as mere glimmers of light, which, viewed with

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<v Speaker 1>a more powerful telescope, separate into clusters of distant stars.

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<v Speaker 1>The most common shape of these clusters is globular to

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<v Speaker 1>the eye, appearing simply round. Stars gather densely near the

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<v Speaker 1>center and gradually open out to a thin scattering about

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<v Speaker 1>the edge. Thousands of suns are often thus collected into

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<v Speaker 1>one cluster. The clusters are to be seen in all

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<v Speaker 1>parts of the sky, but the greater number seen to

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<v Speaker 1>be gathered into the space covered by the Milky Way

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<v Speaker 1>and by the famous South Magellanic clouds, some of them

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<v Speaker 1>utifully colored, as for instance, a cluster in Tucan not

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<v Speaker 1>visible from England, the center of which is rose colored

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<v Speaker 1>bordered with white. No doubt it contains a large number

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<v Speaker 1>of bright red suns surrounded by scattering of white suns.

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<v Speaker 1>By some it is supposed that many of these clusters

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<v Speaker 1>may be other vast galaxies of stars, more or less

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<v Speaker 1>like the Milky Way, lying at enormous distances from us. Others,

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<v Speaker 1>on the contrary, rather maintain that such clusters, instead of

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<v Speaker 1>being separate universes from our own, are merely lesser star

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<v Speaker 1>systems included within our great stellar system, and probably all

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<v Speaker 1>traveling round some one center. For the present, this must

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<v Speaker 1>be considered an open question. But in either case, if

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<v Speaker 1>worlds are journeying among the suns of such a starry cluster,

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<v Speaker 1>what sights might not be witnessed by their possible inhabitants.

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<v Speaker 1>We do not, indeed know the distances between the separate

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<v Speaker 1>suns of a cluster, which may be far greater than

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<v Speaker 1>appears to us. Yet on the other hand, it may

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<v Speaker 1>well be that there are near enough together to shed

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<v Speaker 1>bright light on all sides of a planet revolving in

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<v Speaker 1>their midst The planet might or might not have within

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<v Speaker 1>view a single sun equal in apparent size to our

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<v Speaker 1>Sun as seen from Earth. Yet thousands of lesser suns

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<v Speaker 1>shining night and day would cause a radiance which we

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<v Speaker 1>never enjoy. No not night. In such a world, there

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<v Speaker 1>could be no night. Worlds in the midst of a

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<v Speaker 1>star cluster must be regions of perpetual day, no night,

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<v Speaker 1>no starry heaven, no sunrise lights or sunset glories, no

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<v Speaker 1>shadow mingling with sunshine, but one continual, ceaseless blaze of brightness.

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<v Speaker 1>We can hardly picture, even in imagination, such a condition

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<v Speaker 1>of things. Besides star clusters, there are also nebulaie. The

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<v Speaker 1>word nebula comes from the Latin word for cloud, and

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<v Speaker 1>the nebulae are so named for their hazy and cloudlike appearance.

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<v Speaker 1>It is not always easy at first sight to distinguish

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<v Speaker 1>between nebulaie and very distant star clusters. Both have the

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<v Speaker 1>same dim or cloudy look. In days gone by, the

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<v Speaker 1>star clusters were often included by astronomers under the general

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<v Speaker 1>term of nebulae, and, as with star clusters, so with

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<v Speaker 1>many nebulaie. More powerful telescopes have shown them to be

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<v Speaker 1>great systems or collections of innumerable stars, crowded together by

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<v Speaker 1>vastness of distance. But although some nebulaie are really to

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<v Speaker 1>a certain extent, much the same as star clusters. Others

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<v Speaker 1>are entirely differ. The spectroscope, by its delicate test, proves

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<v Speaker 1>them to consist of enormous masses of glowing gas, and

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<v Speaker 1>not to be solid bodies at all, even in the

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<v Speaker 1>limited sense in which we may call our sun a

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<v Speaker 1>solid body. Whether they are on their road to become

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<v Speaker 1>solid bodies by and by is another question. Certainly they

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<v Speaker 1>are not so yet. By glowing gas, I do not

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<v Speaker 1>mean burning gas, like the gas alight at a chandelier burner.

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<v Speaker 1>For actual burning, for being consumed and wasting away an

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<v Speaker 1>atmosphere such as ours, is necessary. The gases which compose

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<v Speaker 1>the outer envelopes of sun and stars, and the gases

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<v Speaker 1>which compose the whole body of many a nebula shine

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<v Speaker 1>with intensity of glowing but not consuming heat, and this

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<v Speaker 1>is termed incandescence. The number of nebulaie now known amounts

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<v Speaker 1>to thousands. There are usually divided into classes according to

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<v Speaker 1>their apparent shapes as seen from Earth. There are circular nebulaie,

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<v Speaker 1>oval nebulaie, anular nebulaie, conical nemuli, comentary nebuli, spiral nebulaie,

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<v Speaker 1>and nebulae of divers other descriptions. These apparent shapes would

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<v Speaker 1>doubtless change greatly if we could look upon them from

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<v Speaker 1>some other standpoint and at a lessened distance. Even when

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<v Speaker 1>seen in more powerful telescopes, they often wear a totally

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<v Speaker 1>different aspect. Many nebulae are believed to lie in incalculable distances,

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<v Speaker 1>and the light which comes to us from them may

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<v Speaker 1>have been hundreds of years upon its road, but opinions

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<v Speaker 1>differ much on this question. Some astronomers place many of

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<v Speaker 1>the nebulai as a matter of probability, far outside the

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<v Speaker 1>vast stellar system to which we, while others believe the

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<v Speaker 1>most of it. Not all of the gas's nebulae are

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<v Speaker 1>included within the bounds of our own particular starry universe.

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<v Speaker 1>Mention must be made of the great nebula in Orion.

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<v Speaker 1>The middle star of Orion's sword handle, when carefully noted

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<v Speaker 1>with the naked eye, can be seen to have a

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<v Speaker 1>slightly misty aspect. This, seen in powerful telescopes, develops into

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<v Speaker 1>a glorious nebulae, one of the grandest in our heavens.

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<v Speaker 1>It is shown by the spectroscope to consist partly of stars,

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<v Speaker 1>partly of glowing gas of countless suns, possibly not large

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<v Speaker 1>in size, but great in numbers, bathed in and surrounded

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<v Speaker 1>by a stupendous mass of glowing gas hydrogen gas, nitrogen gas,

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<v Speaker 1>in one other gas, the nature of which we do

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<v Speaker 1>not know. As for the size of this nebula, we

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<v Speaker 1>are driven to conjecture, but undoubtedly it is enormous. Measurement

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<v Speaker 1>of size is impossible where a measurement of distance cannot

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<v Speaker 1>be accomplished. It has, however, been suggested that if a

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<v Speaker 1>ball be imagined so huge as to fill the entire

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<v Speaker 1>circle of our Earth's annual pathway round the Sun, one

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<v Speaker 1>million of such vast globes of light might be less

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<v Speaker 1>in size than the nebula in Orion. How much larger

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<v Speaker 1>yet it may be. None can venture to say. Another

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<v Speaker 1>famous nebula is that in Andromeda. It can be seen

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<v Speaker 1>by the naked eye, and has been sometimes taken for

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<v Speaker 1>a comet. The spectroscope shows this nebula to be formed

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<v Speaker 1>seemingly not of glowing gas, but of multitudinous faint stars,

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<v Speaker 1>so it is more akin to an ordinary star cluster.

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<v Speaker 1>Before quitting this subject, illusion should be made to the

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<v Speaker 1>famous Bagelinic clouds in the southern heavens. Sometimes they are

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<v Speaker 1>called the cape clouds. They differ from other nebulae in

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<v Speaker 1>many points, and more particularly in their apparent size. The

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<v Speaker 1>Great cloud is about two hundred times the size of

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<v Speaker 1>the full moon, while the small cloud is about one

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<v Speaker 1>quarter as large. In appearance, they are not unlike two

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<v Speaker 1>patches of the Milky Way, separated and moved to a

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<v Speaker 1>distance from the main stream. These clouds are surrounded by

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<v Speaker 1>a very barren portion of the heavens, containing few stars,

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<v Speaker 1>but in themselves they are particularly rich. Seen through a

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<v Speaker 1>powerful telescope, they are found to abound with stars. The

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<v Speaker 1>Greater Cloud alone contains over six hundred from the seventh

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<v Speaker 1>to the tenth magnitudes, countless tiny star points of lesser magnitudes,

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<v Speaker 1>star clusters of all descriptions, and nearly three hundred nebulae,

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<v Speaker 1>all crowded into this seemingly limited space. End of Section

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<v Speaker 1>twenty five.