Space Glossary

Big Bang

The origin of the universe; in the Big Bang, the observable universe expanded rapidly from a single point

black hole

an object that has gravity so strong that even light can’t escape it. Black holes form in supernova explosions of stars with more than 20 times the mass of the sun

galaxy

a group of millions or billions of stars held together by gravity. The Solar System is a part of the Milky Way Galaxy

large star 

A star with more than 8 times the mass of the Sun. A large star becomes a red supergiant and explodes in a supernova, leaving behind either a black hole or a neutron star. 

light-year

A unit of length equal to the distance light travels in one year. One light year is 9,460,500,000,000 kilometres. It is used to measure large distances in space

main sequence star

A star that is fusing hydrogen and in a stable state. Main sequence stars are stable because the outward force of fusion is balanced by the inward force of gravity. 

moon

A natural satellite that orbits a planet. Earth has one moon, Mars has two and Jupiter has over 60.

Nebula

A vast cloud of gas and dust in outer space. Stars form in nebulas and can also produce nebulas when they die

Neutron Star

The remains of the core of a large star, made of densely packed neutrons. Neutrons stars form in supernova explosions of stars with 8-20 times the mass of the sun

Nuclear fusion

A nuclear reaction in which two atomic nuclei join together. Nuclear fusion occurs in the cores of stars A heavier nucleus is formed and light and heat are released.

Nuclear Reaction

A reaction in which an atoms nucleus changed. If an atom gains or loses protons in a nuclear reaction, it changes from one element to another 

Planet

A natural satellite that orbits a star. A planet must be large enough to be round and have cleared its orbit of debris 

Planetary nebula

A nebula formed from a red giant star. Planetary nebulas form from red giants that have expanded until their outer gas layers drift out into space. 

Protostar 

A dense ball of gas that hasn’t yet developed into a star. Protostars form in nebulas. Once they start to fuse hydrogen, they become main sequence stars. 

Red giant

a small star that fuses helium, causing it’s outer layers to expand. The outer layers of a red giant drift outwards into space to form a planetary nebula.

Red supergiant 

A large star that fuses helium causing its outer layers to expand. Red super giants eject most of their mass in catastrophic explosions known as supernovas. 

Redshift

The stretching of light waves emitted by objects moving away from us. Redshift provides evidence that galaxies are moving away from us as the universe expands. 

Small star

A star with less than 8 times the mass of the Sun. A small star becomes a red giant and leaves behind a white dwarf surrounded by a planetary nebula.

star

a hot, bright ball of gas held together by gravity. A stars light and heat are produced by nuclear fusion in its core. 

Sun 

The star at the centre of the Solar System. The Sun is a small star that makes up more than 99% of the Solar System’s total mass. 

supernova

An explosion of a red supergiant star. A supernova star blasts matter into space and leaves behind either a neutron star of a black hole.

universe 

All of space and time, and the matter and energy they contain. The observable universe is limited by the time it takes light to travel from distant galaxies to our telescopes. 

white dwarf

the remains of the core of a small star. A white dwarf forms when a red giant loses its outer layers and fusion stops.