Orbital inclination

A diagram of Keplerian orbital elements.

Orbital inclination is a term for the angle between two orbital planes. It is often used to describe the movement of celestial bodies such as stars and planets.

One of the planes is the standard, or reference. The galactic plane of a galaxy is often used as the reference.

• For a planet's orbit, the inclination is the angle to the ecliptic plane.
• For a moon, an inclination of 0 degrees means the orbiting body orbits the planet in its equatorial plane, in the same direction as the planet rotates.