Orbital Plane (astronomy)

Orbital Plane (astronomy)

The orbital plane of an object orbiting another is the geometrical plane in which the orbit lies. The orbital plane is defined by two parameters, Inclination (i) and Longitude of the ascending node (Ω). Three non-collinear points in space suffice to determine the orbital plane. A common example would be: the center of the heavier object, the center of the orbiting object and the center of the orbiting object at some later time.

All of the planets, comets, and asteroids in the Solar System are in orbit around the Sun. The orbital planes of all those orbits nearly line up with each other, making a semi-flat disk called the invariable plane of the Solar System.

By definition the inclination of a planet in the solar system is the angle between its orbital plane and the orbital plane of the Earth (the ecliptic). In other cases, for instance a moon orbiting another planet, it is convenient to define the inclination of the moon's orbit as the angle between its orbital plane and the planet's equator.