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Astronomy for Kids

Glossary and Terms

Asteroid - An asteroid is a celestial body made of rock and metal that orbits the Sun. Asteroids can vary in size from a few feet across to hundreds of miles.

Asteroid belt - An area between the orbits of Mars and Jupiter where millions asteroids orbit the Sun.

Astronaut - A person who is specially trained to travel into outer space.

Astronomical Unit (AU) - A measure of distance used for outer space. One AU is equal to 149.6 million kilometers which is the mean distance from the center of the Sun to the center of the Earth.

Astronomy - The branch of science that studies outer space, celestial bodies, and the universe.

Atmosphere - An envelope of gases that surround a planet.

Black hole - An area in space with gravity so intense even light cannot escape its pull. Black holes are formed when massive stars collapse.

Celestial body - An natural object that exists outside the Earth's atmosphere. Examples include stars, planets, asteroids, comets, and meteoroids.

Constellation - A grouping of stars that form a pattern in the sky when viewed from Earth.

Coma - The area of gases and dust that form around a comet as it passes by the Sun.

Comet - A celestial body made of ice and rock that orbits the Sun. When a comet nears the Sun a coma and tail of gases and dust can be seen.

Cosmology - The branch of science that studies the origin and nature of the universe.

Dwarf planet - A celestial body that is large enough to become rounded from its own gravity, but has not cleared its orbital region of other objects.

Eclipse - When one celestial body blocks the light of the Sun from another. In a solar eclipse, the Moon blocks the light of the Sun from the Earth. In a lunar eclipse, the Earth blocks the light of the Sun from the Moon.

Galaxy - A system consisting of a large number of stars bound together by gravity.

Gas giant - A large planet that is not composed mostly of rock, but primarily of gas. There are four gas giants in the Solar System including Jupiter, Saturn, Uranus, and Neptune.

Kuiper belt - A large ring of millions of icy objects that exists outside the orbit of Neptune.

Light year - A measure of length that equals the distance light travels one year in a vacuum. It is about 5.8 trillion miles.

Meteor - A meteoroid that has entered the Earth's atmosphere is called a meteor.

Meteorite - A meteor becomes a meteorite when it reaches the ground.

Meteoroid - A small rocky object that orbits the Sun that has broken off from a comet or asteroid.

Milky Way - The galaxy that contains the Solar System.

Nebula - A large cloud of dust in space. The dust in nebulae often forms stars and planets.

Nuclear fusion - The process by which two or more atoms are joined together to form a larger atom. This process occurs inside stars and produces huge amounts of energy.

Oort cloud - A band of billions of icy objects that exists at the edge of the Solar System.

Orbit - The path a celestial object takes around a star or planet.

Planet - A large celestial object that has become rounded due to its gravity and has cleared is nearby region of other smaller objects. Planets in the solar system include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Satellite - A natural or artificial object that is in orbit around a planet.

Solar System - The Solar System consists of the Sun and all the objects that orbit around it including the planets, asteroids, comets, and other objects.

Solar Wind - A stream of charged particles that is constantly flowing from the Sun.

Star - A giant ball of hot gas and plasma that generates huge amounts of energy through nuclear fusion.

Sunspot - A dark area on the Sun caused by cooling from electromagnetic activity within the Sun.

Supernova - A huge explosion caused when a star collapses on itself.

Telescope - An instrument used to view objects in outer space.

Universe - The universe is everything that exists including the stars, planets, matter, energy and time.

More Astronomy Subjects

The Sun and Planets
Solar System

Black Holes
Meteors and Comets
Sunspots and Solar Wind
Solar and Lunar Eclipse

Space Exploration Timeline
Space Race
Nuclear Fusion
Astronomy Glossary

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