Astronomical terms and our solar system

Guide to the solar system

  • The universe consists of many galaxies separated by empty space.
  • A galaxy is a large cluster of stars (eg the Milky Way).
  • A star 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 system. A solar system consists of a central star orbited by planets.
  • A planet is a large ball of matter that orbits a star (eg Earth or Jupiter). Planets do not emit light themselves.
  • An exoplanet is a planet existing around another star, outside of our solar system
  • Many planets have moons which are natural satellites. 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 planet is an object that orbits a star but is not large enough or roughly spherical enough to be classed as a small planet.
  • An asteroid is an orbiting object which is even smaller than a dwarf planet.
Planets of the solar system arranged in order of distance from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

Gravity on other planets