A Textbook of General Astronomy

1. Astronomy is the science which treats of the heavenly bodies. As such bodies we reckon the sun and moon, the planets (of which the earth is one) and their satellites, comets and meteors, and finally the stars and nebulae.

We have to consider in Astronomy:
(a) The motions of these bodies, both real and apparent, and the laws which govern these motions.
(b) Their forms, dimensions, and masses.
(c) Their nature and constitution.
(d) The effects they produce upon each other by their attractions, ...