Orbit Facts



  • Orbit means travel round, and a moon, planet or other space object may be held within a larger space object’s gravitational field and orbit it.
  • Orbits may be circular, elliptical (oval) or parabolic (conical). The orbits of the planets are elliptical.
  • An orbiting space object is called a satellite.
  • The biggest-known orbits are those of the stars in the Milky Way, which can take 200 million or more years.
  • Momentum is what keeps a satellite moving in space. How much momentum a satellite has depends on its mass and its speed.
  • A satellite orbits at the height where its momentum exactly balances the pull of the larger object’s gravity.
  • If the gravitational pull is greater than a satellite’s momentum, it falls in towards the larger space object.
  • If a satellite’s momentum is greater than the pull of the larger object’s gravity, it flies off into space.
  • The lower a satellite orbits, the faster it must travel to stop it falling in towards the larger space object.
  • Geostationary orbit for one of Earth’s artificial satellites is 35,786 km over the Equator. At this height, it must travel around 11,000 km/h to complete its orbit in 24 hours. Since Earth also takes 24 hours to rotate, the satellite spins with it and so stays in the same place over the Equator.