Astronomy Glossary and Terms
Asteroid: An asteroid is a celestial body composed of rock and metal that orbits the Sun. Asteroids can range in size from a few feet to hundreds of kilometers.
Asteroid Belt: The area between the orbits of Mars and Jupiter, where millions of asteroids orbit the Sun.
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Astronaut: A person specially trained to travel in space.
Astronomical unit (AU): A unit of distance used for outer space. One AU is equivalent to 149.6 million km, the average distance between the center of the Sun and the center of the Earth.
Astronomy – The science that studies outer space, celestial bodies, and the universe.
Atmosphere – A layer of gas surrounding a planet.
Black Hole – An area in space that has such a strong gravitational pull that even light cannot escape its gravitational pull. Black holes form when massive stars collapse.
Celestial Body – A natural object that exists outside the Earth’s atmosphere. Examples include stars, planets, asteroids, comets, and meteorites.
Constellations – A group of stars that form a pattern in the sky as seen from Earth.
Coma – An area of gas and dust that forms around a comet as it passes close to the Sun.
Comet – A celestial body consisting of ice and rock orbiting the Sun. As a comet approaches the Sun, commas and tails of gas and dust can be seen.
Cosmology – The science that studies the origin and nature of the universe.
Dwarf Planet – A celestial body that is large enough to round under its own gravity, but has not cleared its orbit for other objects.
Eclipse – When one celestial body blocks sunlight from another. During a solar eclipse, the Moon blocks sunlight coming from Earth. During a lunar eclipse, the Earth blocks sunlight from the Moon.
Galaxy – A system made up of a large number of stars bound together by gravity.
Gas Giant – A large planet that is not composed mainly of rocks but is mostly gas. There are four gas giant planets in the solar system, including Jupiter, Saturn, Uranus, and Neptune.
Kuiper Belt – A large belt of millions of icy objects that exists outside the orbit of Neptune.
Light year: A measure of the length of the distance light travels in a year in a vacuum. That’s about 5.8 trillion miles.
Meteor: A meteor that has entered the Earth’s atmosphere is called a meteor.
Meteorite – A meteorite becomes a meteor when it hits the ground.
Meteoroid – A small rocky object orbiting the Sun that has separated from a comet or asteroid. Milky Way – The galaxy that contains the solar system.
Nebula – A large dust cloud in space. Dust from nebulae often forms stars and planets.
Nuclear Fusion – Process in which two or more atoms are bonded together to form a larger atom. This process occurs inside stars and creates a huge amount of energy.
Oort Cloud – A band of billions of icy objects that exist on the outskirts of the solar system.
Orbit – A celestial body’s path around a star or planet.
Planet – A large celestial body that has rounded due to its gravity and cleared its vicinity from other smaller objects. The planets of the solar system include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Satellite: A natural or man-made object orbiting a planet.
Solar System – The Solar System includes the Sun and all the objects that orbit it, including planets, asteroids, comets, and other objects.
Solar Wind – A constant stream of charged particles from the Sun.
Star – A giant ball of hot gas and plasma that generates large amounts of energy through nuclear fusion.
Sunspot: A dark area on the Sun caused by cooling caused by the Sun’s electromagnetic activity.
Supernova – A massive explosion that occurs when a star collapses on its own.
Telescope – Instrument used to observe objects in space.
Universe – The universe is everything that exists, including stars, planets, matter, energy, and time.