Explain why a geostationary satellite always remains above the same point on the Earth's surface.

AQA GCSE Physics (8463) — 4.8.1 Solar system; stability of orbital motions; satellites (Phys only) · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Communications satellites are placed in geostationary orbits above the equator. These satellites are used to relay television signals to homes across large areas of the Earth.

Model answer (4 marks)

A geostationary satellite has an orbital period of 24 h, which is the same as the Earth's rotation period. It orbits in the same direction as the Earth's spin and lies in the equatorial plane. Because its period matches the Earth's rotation, the satellite and the point on the surface move together, keeping the same relative position. Thus the satellite appears stationary above that point.

Examiner tips

  • State the 24‑hour period and match it to Earth's rotation
  • Mention the equatorial, same‑direction orbit
  • Explain the relative motion keeps the satellite fixed
  • Use clear, concise sentences

Common mistakes

  • Forgetting to mention the 24‑hour period
  • Not specifying that the orbit is in the equatorial plane
  • Confusing the satellite’s motion with the Earth's rotation direction

Mark scheme (4 marks)

  1. A geostationary satellite has an orbital period of 24 hours
  2. This matches the rotation period of the Earth
  3. The satellite orbits in the same direction as the Earth's rotation
  4. Because the satellite and the point on the surface move together / keep the same relative position, the satellite appears stationary from the ground

Key terms in this question

geostationary satellite

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