The angle between a satellite’s orbital plane and the Earth’s equatorial plane is known as which orbital element?

• A. Period
• B. Eccentricity
• C. Semimajor axis
• D. Inclination

Answer: (D)

The concept being tested is orbital inclination—the tilt of the orbit relative to Earth's equator. It is defined as the angle between the satellite’s orbital plane and the equatorial plane. This tells you how the path through space is oriented around the planet. For example, an inclination of 0 degrees means the orbit lies right on the equator and moves prograde, while 90 degrees is a polar orbit that climbs over the poles, and 180 degrees is a retrograde equatorial path. The other common orbital elements describe different aspects: period is how long a satellite takes to complete one orbit (time-based, tied to size and gravity), eccentricity describes how stretched or circular the orbit is (shape), and the semimajor axis describes the overall size of the orbit. So the angle between the orbital plane and the equatorial plane is specifically the inclination.