perigean

Perigean is an adjective relating to perigee, the point in an object’s elliptical orbit around a planet where the object is nearest to that planet. The term derives from peri-, meaning near, and -ge, meaning Earth, and is widely used in astronomy and space science to describe phenomena associated with the closest approach to a planet.

In practice, perigean is most often applied to the Moon’s orbit around Earth, though it can describe any satellite or spacecraft in an elliptical orbit. At perigee the distance to the planet is smaller than at any other point in the orbit, with the opposite point being apogee. The Moon’s perigee distance changes slightly over time due to gravitational perturbations from the Sun and other bodies, and is a factor in predicting tides and orbital dynamics. Perigee and apogee are the standard terms for the closest and farthest points, while periapsis and apoapsis serve as more general equivalents for orbits around any primary body.

Perigean tides are a notable application of the concept, occurring when the Moon is near perigee at the times of full or new Moon, which can produce higher-than-normal tides on Earth. In orbital engineering and observation, perigean passages can influence considerations such as tidal forces, satellite visibility, and orbital decay.

Overall, perigean emphasizes proximity to the planet at the closest orbital approach and is primarily used in celestial mechanics and related fields.