Astronomical object

“ Picture the tiny waves of light crossing the countless billions of miles of space during those two thousand years, and reaching us so widely spread out that the few faint rays which strike our eye are quite useless, and for us that star has no existence; we cannot see it. Then go and ask the giant telescope, by turning the object-glass in the direction where that star lies in infinite space. The widespread rays are collected and come to a minute bright image in the dark tube. ”

“ The geocentric system of astronomy, with its eccentrics and its epicycles, was an hypothesis utterly at variance with fact, which nevertheless did great things for the advancement of astronomical knowledge. ”

“ Our sun occupies a somewhat central position in the system. The stars are classed into sizes, as first magnitude, second magnitude, &c., on to the thirteenth or fourteenth magnitude, but all beyond the fifth magnitude (by far the greater number) are only visible by the aid of the telescope. There are about 5000 stars visible to the naked eye. ”

“ If now the stars be regarded as motionless and the sun be moving towards a particular point on the celestial sphere, then by an obvious effect of perspective the stars near that point will appear to recede from it and one another on the celestial sphere, while those in the opposite region will approach one another, the magnitude of these changes depending on the rapidity of the sun's motion and on the nearness of the stars in question. ”

“ Those wonderful varieties in the appearance of the solar surface which have so long perplexed astronomers, not only supply in themselves interesting subjects of observation and examination, but gain an enhanced meaning from the consideration that they speak meaningly to us of the structure of an orb which is the source of light and heat enjoyed by a series of dependent worlds whereof our earth is—in size at least—a comparatively insignificant member. ”

“ Moreover modern astronomers, as well as ancient, find it convenient for very many purposes to make use of this sphere, though it has no material existence, as a means of representing the directions in which the heavenly bodies are seen and their motions. ”

“ GRAVITATIONAL ASTRONOMY IN THE 18TH CENTURY.
"Astronomy, considered in the most general way, is a great problem of mechanics, the arbitrary data of which are the elements of the celestial movements; its solution depends both on the accuracy of observations and on the perfection of analysis."
Laplace, Preface to the Mécanique Céleste. 228. The solar system, as it was known at the beginning of the 18th century, contained 18 recognised members: the sun, six planets, ten satellites (one belonging to the earth, four to Jupiter, and five to Saturn) , and Saturn's ring. ”

“ The study of the motion of the stars along the line of sight, by means of photographs of their spectra, is now the favorite investigation at nearly all the great observatories of the world. The study of the surfaces of the planets, while the favorite subject with the public, next to the destruction of the earth by a comet, does not seem to appeal to astronomers. ”

“ With regard to the moon, sun, and some of the planets, in addition to their form and size, we have been able, by this means, to obtain some slight knowledge of their physical structure. But, with reference to the myriads of stars, clusters, and nebulæ, which people the depths of space, the telescope reveals little more than variety in color, brightness, and shape. ”

“ The reflection of the rays of light is that property by which—after approaching the surfaces of bodies, they are thrown back, or repelled. It is in consequence of this property that all the objects around us, and all the diversified landscapes on our globe, are rendered visible. It is by light reflected from their surfaces that we perceive the planetary bodies and their satellites, the belts of Jupiter, the rings of Saturn, the various objects which diversify the surface of the Moon, and all the bodies in the universe which have no light of their own. ”

“ Stars which have bright lines in their spectra (§ 312) form another link connecting nebulae with stars. A good many converging lines of evidence thus point to a greater variety in the arrangement, size, and structure of the bodies with which the telescope makes us acquainted than seemed probable when sidereal astronomy was first seriously studied; they also indicate the probability that these bodies should be regarded as belonging to a single system, even if it be of almost inconceivable complexity, rather than to a number of perfectly distinct systems of a simpler type. ”

“ Even Jupiter and Venus, and the sun and moon, are sometimes calculated on this scale of stellar magnitude, numerically negative, of course, Venus sometimes being as bright as magnitude -4.3, and the sun -26.7.
Knowing thus the relation of sun, moon, and stars, and the number of the stars of different magnitudes, it is possible to estimate the total light from the stars. This interesting relation comes out this way: that the stars we cannot see with the naked eye give a greater total of light than those we can because of their vastly greater numbers. ”

“ If an observer looks at the stars on any clear night he sees an apparently innumerable [1] host of them, which seem to lie on a portion of a spherical surface, of which he is the centre. This spherical surface is commonly spoken of as the sky, and is known to astronomy as the celestial sphere. The visible part of this sphere is bounded by the earth, so that only half can be seen at once; but only the slightest effort of the imagination is required to think of the other half as lying below the earth, and containing other stars, as well as the sun. ”

“ The “flying synods of worlds” formed by them must gravitate one towards another as if concentrated at their several centres of gravity. Accordingly, “a star, or sun, such as ours, may have a proper motion within108 its own system of stars, while the whole may have another proper motion totally different in quantity and direction.” We may thus, he continued, “arrive in process of time, at a knowledge of all the real, complicated motions of the planet we inhabit; of the solar system to which it belongs; and even of the sidereal system of which the sun may possibly be a member.” ”

“ These bright patches, then, which form the Milky Way, are really groups of stars or star-clusters, and when some of these clusters are photographed through a telescope as many as 15 or 20 thousand stars can be counted, while the real number of stars that lie beyond and which cannot be seen is past all calculation, and, just think of it, every one of these stars is a Sun as large or larger than our Sun! ”

“ Now, the telescope—more than any other invention of man—has tended to open to our view the most magnificent and extensive prospects of the works of God. It has led us to ascertain that, within the limits of the solar system, there are bodies which, taken together, comprise a mass of matter nearly two thousand five hundred times greater than that of the earth—that these bodies are all constituted and arranged in such a manner as to fit them for being habitable worlds—and that the sun, the centre of this system, is five hundred times larger than the whole. ”

“ But smaller instruments reveal only the in-running star streams and the sprinkling of stellar points over the main aggregation, which cause it to sparkle like a cloud of diamond dust transfused with sunbeams. The appearance of flocking together that those uncountable thousands of stars present calls up at once a picture of our lone sun separated from its nearest stellar neighbor by a distance probably a hundred times as great as the entire diameter of the spherical space within which that multitude is congregated. ”

“ In the former case, his telescope makes equally astounding revelations in an opposite direction. The Heavens are swarming with splendid structures unseen to the naked eye: new planets are visible, with rings, belts, and moons, and the stars prove to be resplendent suns; the centres of so many systems peopling infinitude; and these, moreover, obeying laws of motion the same as those which exist in the system of which the earth forms part! ”

“ With a very small telescope, however, this band of luminous matter will be instantly changed into thousands of stars, all separate and distinct, and some of these stars will look about as large as the stars of the Pleiades when these are seen with the naked eye, while others will shine as brightly as Venus or Jupiter when they are nearest to the Earth. ”

“ The number of stars visible in our great telescopes is of the order of one hundred millions. The dark or invisible bodies indicated by several considerations—the planets in the solar system, the spectroscopic binaries, the eclipsing variable stars, and the gravitational power of the universe—should outnumber the bright ones several fold. ”

“ He also detected spots on the sun’s disk, the phases of Venus, and irregularities on the moon’s surface, and declared the Milky Way to be composed of a countless tract of separate stars.
When we remember the limited power of the telescope of the age, we can but marvel, not at how little, but how much was known regarding the starry skies. ”

“ The obvious fact that the sun, the moon, and the stars rose day by day, moved across the sky in a glorious never-ending procession, and duly set when their appointed courses had been run, demanded some explanation. The circumstance that the fixed stars preserved their mutual distances from year to year, and from age to age, appeared to Ptolemy to prove that the sphere which contained those stars, and on whose surface they were believed by him to be fixed, revolved completely around the earth once every day. ”

“ How much there may be beyond what our telescopes show, we cannot tell ; but what we can know is of unimaginable immensity. In the visible world, the milky way is a tiny fragment; within this frag- ment, the solar system is an infinitesimal speck, and of this speck our planet is a microscopic dot. ”

“ CHAPTER XII STARS AND NEBULÆ
That a science of stellar chemistry should not only have become possible, but should already have made material advances, is assuredly one of the most amazing features in the swift progress of knowledge our age has witnessed. Custom can never blunt the wonder with which we must regard the achievement of compelling rays emanating from a source devoid of sensible magnitude through immeasurable distance, to reveal, by its distinctive qualities, the composition of that source. ”

“ They thus had a telescope more than three hundred feet long as immovable as the solid earth, but, alas for their calculations, the star itself shifted its position, and their gigantic observing tube became useless until modern science inferred from its position the date of their building. How imposing to the imagination this association between a particular star and the mightiest structure made by human hands on the earth! ”

“ The milky look of the background of the Galaxy is, of course, caused by the intermingled radiations of inconceivably minute and inconceivably numerous stars, thousands of which become separately visible, the number thus distinguishable varying with the size of the instrument. But the most powerful telescope yet placed in human hands can not sound these starry deeps to the bottom. ”

“ We must remember that these stars will appear in the field of view simply as two tiny points of light. The astronomer, as we have said, is provided with a simple system of long rods, by means of which he can manipulate the semi-lenses while the observation is being made. If he slides them very slowly one way or the other, the two star-points in the field of view will be seen to approach each other. In this way they can at last be brought so near together that they will form but a single dot of light. ”

“ It had long been recognised that as the earth describes a vast orbit, nearly two hundred million miles in diameter, in its annual journey round the sun, the apparent places of the stars should alter, to some extent, in correspondence with the changes in the earth's position. The nearer the star the greater the shift in its apparent place on the heavens, which must arise from the fact that it was seen from different positions in the earth's orbit. ”

“ We observe the star with the mural circle while the earth is in the position E'. We apply the corrections for precession, nutation, aberration, and refraction; and we shall know what the corrected position of that star should be half a year hence, as observed when the earth is at E'". Now, suppose we go to this second state of things, and when the earth is at E"', we observe the meridional zenith distance of the star, we correct it for refraction, precession, nutation, and aberration. ”

“ These two persons, at certain appointed times, should (as near as could be) both at the same time, observe the way of the Moon, Mars, Venus, Jupiter, and Saturn, amongst the fixt Stars, with a good large Telescope, and making little Iconismes, or pictures, of the small fixed Stars, that appear to each of them to lye in or near the way of the Center of the Planet, and the exact measure of the apparent Diameter; from the comparing of such Observations together, we might certainly know the true distance, or Parallax, of the Planet. ”

“ What terms too grand to describe the lofty speculations of the astronomer, who points his telescope to some dark point in the blue sky, and descries in its infinite depths a cluster of closely aggregated shining particles, minute as the motes in the sunbeam, and hails it as the discovery of a new system of worlds. He cannot count them, for they are innumerable. ”

“ The instrument was turned in answer to these questions to the sidereal heavens. No other branch of [pg 182] science has been prosecuted in the after half of this century with more zeal and success than has the spectroscopic analysis of the fixed stars. These are known by the telescope to have the character of suns. The most general fact of the visible heavens is the plentiful distribution of suns. They sparkle everywhere as the so-called fixed stars. To them the telescope has been virtually turned in vain. ”