An astronomer is an individual who studies the universe primarily using telescopes. Astronomers rely on both observations of celestial objects, including planets, stars, and galaxies, and physical theories to better understand how these objects formed and work. Although professional astronomers conduct most astronomy research today, amateur sky watchers continue to play a key role.

Astronomy has been practiced since the beginning of recorded history. Many ancient civilizations employed people with some knowledge of the night sky and the motions of the Sun and Moon, although in many cases the identities of these ancient astronomers have long since been lost. At that time the work of astronomers had both practical importance, in the form of keeping track of days, seasons, and years, as well as religious implications. Astronomers did not emerge as true scientists until the Renaissance, when new observations and theories by astronomers such as Nicholas Copernicus (1473-...