384400

384,400 is a numeric value most commonly associated with the distance between the Earth and the Moon. It represents the approximate mean distance, effectively the Moon’s orbital semi-major axis around Earth, expressed in kilometers. In miles, the distance is about 238,855.

The distance is not fixed. The Moon’s orbit is elliptical and subject to perturbations, so the actual Earth–Moon distance varies over the month. It ranges roughly from 363,300 km at perigee (closest approach) to about 405,500 km at apogee (farthest distance). The 384,400 km figure is a convenient average used in science and education.

Modern measurements, including lunar laser ranging which uses retroreflectors left on the Moon, have refined the understanding of the Earth–Moon distance and the dynamics of their interaction. These measurements help improve precise ephemerides, models of tidal effects, and our understanding of orbital evolution.

The figure is widely cited in science references as a standard reference distance and is frequently used in spaceflight planning and communication calculations. While it serves as a useful general benchmark, mission design and navigation rely on time-dependent distance values that account for the Moon’s orbital position at a given moment.