Astronomy is a natural science that studies celestial objects and phenomena, such as stars, planets, comets, galaxies, and the cosmic microwave background radiation. It applies mathematics, physics, and chemistry to explain the origin and evolution of these objects. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets.
Astronomy is one of the oldest natural sciences. Early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included diverse disciplines such as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often synonymous with astrophysics.
Modern astronomy is divided into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, which is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical work seeking to explain observational results and observations being used to confirm theoretical results.