Lunar orbit

In astronomy, lunar orbit (also known as a selenocentric orbit) is the orbit of an object around the Moon.

As used in the space program, this refers not to the orbit of the Moon about the Earth, but to orbits by spacecraft around the Moon. The altitude at apoapsis (point farthest from the center of attraction) for a lunar orbit is known as apolune, apocynthion, or aposelene, while the periapsis (point closest to the center of attraction) is known as perilune, pericynthion, or periselene, from names or epithets of the moon goddess.

Lunar orbit insertion (LOI) is the adjustment to achieve lunar orbit, as undertaken by Apollo spacecraft for example.

Low lunar orbit (LLO) are orbits below 100 km (62 mi) altitude. They have a period of about 2 hours. They are of particular interest in exploration of the Moon, but suffer from gravitational perturbation effects that make most unstable, and leave only a few orbital inclinations possible for indefinite frozen orbits, useful for long-term stays in LLO.