What defines the fixed ground position of a geostationary orbit?

What defines the fixed ground position of a geostationary orbit?

• A. The satellite remains exactly above the equator.
• B. The orbital period matches Earth's rotation.
• C. It must be at a fixed altitude above the poles.
• D. It revolves around the Sun in a year.

Answer: (B)

The defining idea is that a satellite stays fixed relative to a point on Earth only if it completes one orbit in the same time Earth makes one rotation. In other words, the orbital period must equal a sidereal day (about 23 hours 56 minutes). When the satellite’s angular speed matches Earth’s rotation, it stays above the same longitude, appearing stationary from the ground. For this to persist, the orbit must lie in the equatorial plane (zero inclination) so it stays over the equator. The altitude that gives this 24-hour period is about 35,786 kilometers above the surface. The other statements don’t establish a fixed ground position: being over the equator is a consequence of zero inclination, not the defining condition; a fixed altitude above the poles isn’t meaningful for staying stationary relative to Earth, and orbiting the Sun is not relevant to remaining fixed relative to Earth.

The defining idea is that a satellite stays fixed relative to a point on Earth only if it completes one orbit in the same time Earth makes one rotation. In other words, the orbital period must equal a sidereal day (about 23 hours 56 minutes). When the satellite’s angular speed matches Earth’s rotation, it stays above the same longitude, appearing stationary from the ground. For this to persist, the orbit must lie in the equatorial plane (zero inclination) so it stays over the equator. The altitude that gives this 24-hour period is about 35,786 kilometers above the surface. The other statements don’t establish a fixed ground position: being over the equator is a consequence of zero inclination, not the defining condition; a fixed altitude above the poles isn’t meaningful for staying stationary relative to Earth, and orbiting the Sun is not relevant to remaining fixed relative to Earth.