Astronomy: A Revision of Young's Manual of Astronomy - Vol. 1

Astronomy: A Revision of Young's Manual of Astronomy - Vol. 1

Astronomy: A Revision of Young's Manual of Astronomy - Vol. 1

Astronomy: A Revision of Young's Manual of Astronomy - Vol. 1

Excerpt

Astronomy, as is indicated by the Greek roots of the word (ἄστρον, νόμος), is the science which treats of the heavenly bodies. It considers (1) their motions, both real and apparent, and the laws which govern those motions; (2) their forms, dimensions, masses, and surface features; (3) their nature, constitution, and physical condition; (4) the effects which they produce upon one another by their attractions and radiations; (5) their probable past history and future development.

As we look up at night we see in all directions the countless stars, and, conspicuous among them and looking like stars, though very different in their real nature, are scattered a few planets. Here and there appear faintly shining clouds of light, -- the Milky Way, nebulæ, and possibly a comet. Most striking of all, if it happens to be in the heavens at the time, though really the most insignificant of all, is the moon. By day the sun alone is visible, flooding the air with its light and hiding the other objects from the unaided eye, but not all of them from the telescope.

The bodies thus seen from the earth are the heavenly bodies. The first great advance of modern science was the recognition that the earth itself should be counted among these. The earth, like most of the others, is a globe, whirling on its axis and moving swiftly through space, although on its surface we are wholly unconscious of the motion because of its perfect steadiness. Most of the heavenly bodies are so far away that their motions can be detected only by careful observation.

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