Astronomical terms and our solar system
Guide to our solar system
- The UniverseAll the energy and matter that exists. consists of many galaxies separated by empty space.
- A galaxyA cluster of billions of stars, held together by gravity. is a large cluster of stars (eg the Milky Way or Andromeda).
- A starA large mass at the centre of a Solar System (if there are other bodies present) that produces heat and light, eg the star at the centre of our Solar System is called the Sun. is a large ball of matter that is undergoing nuclear fusion and emitting light and other forms of electromagnetic radiation. The Sun is a star.
- The Sun and many other stars have a solar systemThe Sun, its eight orbiting planets, their moons, and other smaller objects which orbit the Sun like asteroids and comets.. A solar system consists of a central star orbited by planets.
- A planetsLarge objects in orbit around a star, but excluding comets and asteroids. is a large ball of matter that orbits a star (eg Earth or Jupiter). Planets do not emit light themselves.
- An exoplanetAn exoplanet is the name given to a planet which orbits a star outside our solar system. is a planet existing around another star, outside of our solar system
- Many planets have one or more moons which are natural satelliteBody that orbits a planet. For example, the Moon is a natural satellite of the Earth but communication satellites are artificial satellites of the Earth.. A moon is a lump of matter that orbits a planet eg the Moon orbits the Earth or Deimos and Phobos orbit Mars.
- A dwarf planetA planetoid that is too small to be considered to be a planet, eg Pluto. is an object that orbits a star but is not large enough or roughly spherical enough to be classed as a small planet. Pluto has been classified as a dwarf planet.
- An asteroidA rock in space. Asteroids orbit the Sun but some may cross the Earth's orbit, producing a small risk of collision. is an orbiting object which is even smaller than a dwarf planet. They are formed of rock and metals. When an asteroid enters a planet's atmosphere, we call it a meteor.
- A cometA ball of icy rock that follows an elliptical orbit around the Sun. is also a relatively small orbiting object composed mainly of ice. They have vast orbits and can take centuries to complete one circuit.