Astronomy is a natural science. It is the study of everything outside the atmosphere of Earth.
It studies celestial objects (such as stars, galaxies, planets, moons, asteroids, comets and nebulae) and processes (such as supernovae explosions, gamma ray bursts, and cosmic microwave background radiation). This includes the physics, chemistry of those objects and processes.
A related subject, physical cosmology, is concerned with studying the Universe as a whole, and the way the universe changed over time.
The word astronomy comes from the Greek words astron which means star and nomos which means law. A person who studies astronomy is called an astronomer.
Astronomy is one of the oldest sciences. Ancient people used the positions of the stars to navigate, and to find when was the best time to plant crops. Astronomy is very similar to astrophysics. Since the 20th century there have been two main types of astronomy, observational and theoretical astronomy. Observational astronomy uses telescopes and cameras to observe or look at stars, galaxies and other astronomical objects. Theoretical astronomy uses maths and computer models to predict what should happen.

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