Astronomy

Astronomy (also called astrophysics or the science of stars) is a natural science that studies phenomena beyond Earth: stars, planets, moons, meteorites, comets, galaxies, and the universe as a whole. The science combines observation, calculation, and physical experiment to understand the structure, properties, and changes of celestial objects.

Astronomy is among the oldest sciences. Ancient civilizations—including Babylon, Egypt, Greece, China, India, and the Islamic world—used stars for timekeeping, agriculture, navigation, and religion. Until the 17th century, astronomy was intertwined with astrology. After the invention of the telescope and the discovery of the laws of gravity, it became an experimental science.

Branches of science

Astronomy has many branches. Planetary astronomy studies the solar system and planets orbiting the sun. Stellar astronomy examines how stars form, shine, and die. Galactic science studies the structure of galaxies, while cosmology investigates the origin, form, and future of the entire universe. Astrophysics uses the laws of physics to explain observations.

Methods of observation

Most astronomers work with electromagnetic radiation and other waves reaching us from space. Visible-light telescopes, radio telescopes, infrared telescopes, X-ray telescopes, and gamma-ray telescopes each reveal different information. Some are built on high mountains where the air is thin; others are launched into space to avoid atmospheric interference with light. Large computers are used for modeling—creating mathematical simulations of celestial phenomena.

Planets orbiting other stars

Since the 1990s, many planets have been discovered orbiting other stars, known as exoplanets. The standard method of discovery is measuring the small dimming of a star's light as a planet passes in front of it (transit), or the slight wobble in a star's motion caused by a planet's gravity. The Extrasolar Planets Encyclopaedia is one of the databases in which scientists record these discoveries.

Public participation

Astronomy is among the sciences to which non-professionals can contribute. Amateur astronomy groups monitor variable stars, search for meteorites, and participate in citizen science projects involving large image datasets. Solar and lunar eclipses also offer the public direct engagement with the science.