Geostationary Orbits (AQA A Level Physics)

Synchronous Orbits

• A synchronous orbit is:

  When an orbiting body has a time period equal to that of the body being orbited and in the same direction of rotation as that body

• These usually refer to satellites (the orbiting body) around planets (the body being orbited)

• The orbit of a synchronous satellite can be above any point on the planet's surface and in any plane

  • When the plane of the orbit is directly above the equator, it is known as a geosynchronous orbit

Geostationary Orbits

Geostationary Orbit

• Many communication satellites around Earth follow a geostationary orbit

  • This is sometimes referred to as a geosynchronous orbit

• This is a specific type of orbit in which the satellite:

  • Remains directly above the equator

  • Is in the plane of the equator

  • Always orbits at the same point above the Earth’s surface

  • Moves from west to east (same direction as the Earth spins)

  • Has an orbital time period equal to Earth’s rotational period of 24 hours

• Geostationary satellites are used for telecommunication transmissions (e.g. radio) and television broadcast

• A base station on Earth sends the TV signal up to the satellite where it is amplified and broadcast back to the ground to the desired locations

• The satellite receiver dishes on the surface must point towards the same point in the sky

  • Since the geostationary orbits of the satellites are fixed, the receiver dishes can be fixed too

Low Orbits

• Some satellites are in low orbits, which means their altitude is closer to the Earth's surface

• One example of this is a polar orbit, where the satellite orbits around the north and south pole of the Earth

• Low orbits are useful for taking high-quality photographs of the Earth's surface. This could be used for:

  • Weather

  • Military applications

Geostationary satellite in orbit