Astronomy is a scientific field concerned with the origin and evolution of celestial objects and phenomena that occur outside Earth's atmosphere. It studies space, celestial bodies and the universe as a whole. It combines observations from evolution, mathematics, physics and chemistry and consists of subfields like astrophysics, astrobiology, cosmology, planetary science, space science, etc. The Units of measurement used in Astronomy are: Astronomical unit, light-year (light-second, light-minute), parsec, kilometers, miles, lunar distance etc. Astronomy is one of the oldest sciences. Objects of interest for study and observation in Astronomy are planets, stars, moons, galaxies, comets, quasars, nebulas, asteroids, black holes. As for the phenomena of interest, they include cosmic radiation, supernova explosion, meteor showers, solar and lunar eclipses, gamma-ray bursts, cosmic winds and others.
Astronomy is one of the oldest of natural sciences which can be split into two branches - observational and theoretical. The word astronomy originates from the Greek word "Astron" which means "star" and "nomia, nomos", which means "law" and the whole meaning of the term is "law of the stars". It should not be confused with astrology, which is recognized as pseudoscience that studies the movement, position and angles of celestial objects and the supposed influence (claimed by astrology) of those positions on human character, behavior, and affairs.