Space Glossary
Essential astronomy terms explained
Asteroid
A rocky body orbiting the Sun, smaller than a planet but larger than a meteoroid. Most asteroids are found in the asteroid belt between Mars and Jupiter.
Black Hole
A region of spacetime where gravity is so strong that nothing, not even light, can escape. Black holes form when massive stars collapse at the end of their lives.
Comet
An icy body that orbits the Sun. When comets approach the Sun, they develop tails of gas and dust that can extend for millions of kilometers.
Constellation
A pattern of stars as seen from Earth. The International Astronomical Union officially recognizes 88 constellations.
Dwarf Planet
A celestial body that orbits the Sun and is spherical in shape, but hasn't cleared its neighboring region of other objects. Examples include Pluto and Eris.
Event Horizon
The boundary around a black hole beyond which nothing can escape. It's not a physical surface but a point of no return.
Galaxy
A massive system of stars, gas, dust, and dark matter bound together by gravity. The Milky Way is our home galaxy.
Light-Year
The distance light travels in one year, approximately 9.46 trillion kilometers. Used to measure vast distances in space.
Nebula
A giant cloud of gas and dust in space. Nebulae are often the birthplace of stars.
Neutron Star
The collapsed core of a massive star, composed almost entirely of neutrons. They are incredibly dense—a teaspoon would weigh billions of tons.
Orbit
The curved path of an object around a star, planet, or moon due to gravity.
Red Giant
A dying star that has exhausted its hydrogen fuel and expanded to enormous size. Our Sun will eventually become a red giant.
Solar System
The Sun and all celestial bodies orbiting around it, including planets, moons, asteroids, and comets.
Star
A luminous sphere of hot plasma held together by gravity, producing light and heat through nuclear fusion.
Supernova
The explosive death of a massive star, briefly outshining entire galaxies. Supernovae distribute heavy elements throughout the universe.