Q.Explain geostationary satellites.

A geostationary satellite orbits directly above the equator with a 24-hour period equal to Earth's rotation, so it always appears at the same point in the sky.

A geostationary satellite is an artificial satellite that orbits the Earth in such a way that it appears stationary when viewed from a fixed point on the Earth's surface.

Conditions required for a satellite to be geostationary:

1. It must revolve in the same direction as the Earth's rotation (west to east).
2. Its orbital plane must coincide with the Earth's equatorial plane (i.e. the orbit is directly above the equator, at zero inclination).
3. Its period of revolution around the Earth must be exactly equal to the Earth's period of rotation about its own axis, i.e. 24 hours (more precisely, one sidereal day, about 23 h 56 min).
4. Its orbit must be circular.

Using the condition that gravity supplies the necessary centripetal force, these conditions fix the orbital radius at about 42,000 km from the Earth's centre, i.e. a height of roughly 36,000 km above the Earth's surface.

…