Astronomy is a natural science that deals with the study of celestial objects (such as stars, planets, comets, nebulae, star clusters and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.

Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments and Stonehenge, and early civilizations such as the Babylonians, Greeks, Chinese, Indians, and Maya performed methodical observations of the night sky. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

Table of contents:

• History of astronomy
• Archaeoastronomy
• Observational astronomy
• Radio astronomy
• Infrared astronomy
• Visible-light astronomy
• Ultraviolet astronomy
• X-ray astronomy
• Gamma-ray astronomy
• Astrometry
• Celestial mechanics
• Sun
• Planetary science
• Planetary geology
• Star
• Galactic astronomy
• Extragalactic astronomy
• Physical cosmology
• Amateur astronomy