Lunar orbit
In astronomy,
lunar orbit refers to 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 various manned or unmanned spacecraft around the Moon. The altitude at apoapsis for a lunar orbit is known as
apolune,
apocynthion or
aposelene, while the periapsis is known as
perilune,
pericynthion or
periselene.
Low Lunar orbit —orbits below 100 kilometres altitude—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.