Geostationary orbit
An orbit around Earth where a satellite's orbital period equals Earth's rotational period (24 hours), so the satellite appears stationary above a fixed point on the equator. The orbital radius is approximately 42,164 km from Earth's centre.
Formula
T² = (4π²/GM)r³
Real World
Sky's broadcast satellites — including Astra 2E above Europe — sit in geostationary orbit at ~35,786 km altitude, allowing a fixed dish on your roof to receive a constant signal without any tracking motor.
Exam Focus
When calculating geostationary radius, use T = 24 hours converted to seconds (86,400 s) and equate gravitational force to centripetal force.
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