Orbital inclination

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.

A diagram of Keplerian orbital elements.

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.