astronomy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The scientific study of matter in outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena.
2. n. A system of knowledge or beliefs about celestial phenomena: the various astronomies of ancient civilizations.

Century Dictionary and Cyclopedia

1. n. The science which describes the heavenly bodies and explains their apparent motions, etc. That part of the science which gives a description of the motions, figures, periods of revolution, and other phenomena of the heavenly bodies is called descriptive astronomy; that part which teaches how to observe their motions, figures, periodical revolutions, distances, etc., and how to use the necessary instruments, is called practical astronomy; and that part which explains the causes of their motions, and demonstrates the laws by which those causes operate, is termed physical astronomy.
2. n. Astrological skill.
3. n. Several other branches of the science are recognized: gravitational astronomy or astronomical mechanics, replacing the term physical astronomy, which is now generally discarded because of the danger of confusion with astronomical physics or astrophysics; nautical astronomy, astronomy applied to navigation; sidereal astronomy, the branch of the science which deals with the stars; spheric astronomy, which treats of the apparent position and motions of bodies on the celestial sphere; theoretical astronomy, which deals with the calculation of orbits and perturbations. These various branches interlace in all directions.

Wiktionary

1. n. The study of the physical universe beyond the Earth's atmosphere, including the process of mapping locations and properties of the matter and radiation in the universe.

GNU Webster's 1913

1. n. obsolete Astrology.
2. n. The science which treats of the celestial bodies, of their magnitudes, motions, distances, periods of revolution, eclipses, constitution, physical condition, and of the causes of their various phenomena.
3. n. A treatise on, or text-book of, the science.

WordNet 3.0

1. n. the branch of physics that studies celestial bodies and the universe as a whole