Geostationary Satellites

As described in NCERT Class 11, Chapter 8 (Gravitation), a geostationary satellite appears stationary relative to a ground observer, which demands three conditions: its orbital period must match the Earth's rotation period of about 24 hours, it must lie in the equatorial plane, and it must revolve in the same direction (west to east) as the Earth's spin. Only then does it stay above a fixed point on the equator. Using Kepler's third law, this 24-hour period fixes the orbital radius at roughly 42,000 km from the Earth's centre, about 36,000 km altitude. The option of a close, any-plane orbit fails because low orbits have periods near 90 minutes. A 12-hour polar orbit cannot stay over one point, as it would track different longitudes. Moving opposite to Earth's rotation would make the satellite drift westward across the sky. As a plausibility check, matching the rotation in both period and direction is the only way an object can hover over a fixed ground location.