Celestial sphere

“ It must be remembered further that the celestial sphere, on which the sun appears to lie, is a mere geometrical fiction introduced for convenience; all that direct observation gives is the change in the sun's direction, and therefore the sun may consistently be supposed to move in such a way as to vary its distance from the earth in any arbitrary manner, provided only that the alterations in the apparent size of the sun, caused by the variations in its distance, agree with those observed, or that at any rate the differences are not great enough to be perceptible. ”

“ 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. ”

“ Nor can such vast movements be urged on in silence; and by the order of nature the shriller notes sound from one extreme of the universe, the deeper from the other. Thus yonder supreme celestial sphere with its clustered stars, as it revolves more rapidly, moves with a shrill and quick strain; this lower sphere of the moon sends forth deeper notes; while the earth, the ninth sphere, remaining motionless, [Footnote: Therefore without sound.] always stands fixed in the lowest place, occupying the centre of the universe. ”

“ This sphere appears to the observer to be very large, though he is incapable of forming any precise estimate of its size.2
Most of us at the present day have been taught in childhood that the stars are at different distances, and that this sphere has in consequence no real existence. The early peoples had no knowledge of this, and for them the celestial sphere really existed, and was often thought to be a solid sphere of crystal. ”

“ The Horizon, the Zenith, and the Meridian. First, let us consider what is the ordinary appearance of the sky. When we go out of doors on a clear night we see the heavens in the shape of a great dome arched above us and filled with stars. What we thus see is one half of the spherical shell of the heavens which surrounds us on all sides, the earth being apparently placed at its centre. The other half is concealed from our sight behind, or below, the earth. This spherical shell, of which only one half is visible to us at a time, is called the celestial sphere. ”

“ Rotation of the Celestial Sphere.—It is well known that the sun and the majority of the stars rise in the east, and set in the west. In our latitude there are certain stars in the north which never disappear below the horizon. ”

“ Upon the sphere, besides the principal circles of the celestial globe, the Zodiac is placed, of a breadth sufficient to contain the apparent path of the moon, with all the stars over which the moon can pass, also the ecliptic, and the heliocentric orbits of all the planets. The Earth in the planetarium has a moveable horizon, to which a large moveable brass circle within the sphere may be set coincident, representing the plane of the horizon continued to the starry heavens. ”

“ The celestial sphere, therefore, as we now possess it, is not simply a collection of unmeaning names, associated with a group of stars in no way connected with them, which have been imposed at various epochs by capricious imagination, but in most instances, if not in all, they embody a history, which, if we could trace it, would probably lead us to astronomical facts, indicating the where and the when of their first introduction ”

“ It is obvious that a movement of the solar system towards one region in the heavens must be accompanied by a general diminution of the distances between the stars in that region and our solar system. On the other hand, the distances from the solar system to the stars at the opposite region of the celestial sphere will be generally increased by such a movement. ”

“ This motion of the heavenly bodies is known to be an apparent one merely, and caused by the turning of our own earth upon its axis. A man standing upon the earth's surface can look up and see above him one-half the great celestial vault, gemmed with twinkling stars, and bearing, perhaps, within its ample curve one or two serenely shining planets and the lustrous moon. But at any given moment the observer can see nothing of the other half of the heavenly sphere. ”

“ The earth thus intersected is called the terrestrial, and the heavens the celestial, sphere. We must bear in mind, that these circles have no existence in Nature, but are mere landmarks, artificially contrived for convenience of reference. On account of the immense distances of the heavenly bodies, they appear to us, wherever we are placed, to be fixed in the same concave surface, or celestial vault. ”

“ They are in a fair state of preservation, the celestial, however, being somewhat damaged through attempts to turn the sphere, which does not move freely on its axis within the meridian and the horizon circle. ”

“ At the center of the sphere, the inner surface of which, as stated above, represented the starry heavens, was placed a small ball, about 15 cm. in diameter, representing the earth. The great globe, driven by water power, was therefore made to appear to revolve around this central terrestrial globe. A representation of the sun, made of glass, had its own proper motion along the circle of the ecliptic, and a representation of the moon likewise was made to move in its own proper course. ”

“ Myriads of luminous globes, placed at immense distances, are the bases which support the fabric of the universe, and millions of opaque globes, which circulate round them, constitute the moving order of its architecture. By two primitive forces, each of which are in continual action, these masses are revolved and carried through the immensity of space; and their combined efforts produce the zones of the celestial spheres, and in the midst of vacuity establish fixed stations, and regular routes and orbits. ”

“ The celestial globe revolves on the axis of the equator, the gores being made to terminate at the poles of the ecliptic. Constellations are represented so far as they have been named by astronomers to date, the several figures being artistically drawn, on which color has been somewhat sparingly employed. ”

“ Celestial globe in which are to be seen more clearly and more distinctly set forth the stars according to their places and positions, that is, their degrees of longitude and latitude where they have been placed in the firmament by the Creator of the Universe. ”

“ Heaven is fashioned on a transcendently large scale. It is not a single sphere, but a universal chain of vast and luminous star-groups, scattered harmoniously throughout the infinite regions of space, so that a part of it lies suspended preciously near to our own Solar System. ”

“ In virtue of this tendency the great orbs which hang suspended in space gravitate toward one another; the moon and the earth fall toward each other, and they both gravitate toward the sun. All the planets of our solar system continually act one on the other, and on the immense sphere which shines at their common focus. By its enormous mass, the sun keeps all of them in their orbits. ”