There is a specific radius required for a geostationary orbit. You can find this using Kepler's 3rd Law , by letting T equal 24 hours (convert to seconds). There is also a specific velocity required to attain this specific radius. You can calculate this using the formula for orbital velocity . As astroman said, given they are moving at the correct velocity and have the correct orbital period, the satellite will be seen as stationary relative to observers on Earth.