Lunar

Lunar is an adjective relating to the Moon or moon-related phenomena. The term comes from Latin Luna, the personification of the Moon in Roman mythology. In the sciences, related terms include selenology (the study of the Moon) and selenography (the mapping and naming of lunar features).

The Moon is Earth’s natural satellite. It orbits at an average distance of about 384,400 kilometers and completes an orbit in roughly 27.3 days (sidereal month). The cycle of lunar phases—the time from one new moon to the next—lasts about 29.53 days (synodic month). The Moon is tidally locked to Earth, so the same hemisphere generally faces Earth.

Phases and eclipses are common lunar concepts. The principal phases are new moon, first quarter, full moon, and last quarter, with waxing and waning intervals in between. A lunar eclipse occurs when Earth lies directly between the Sun and the Moon during a full moon; a solar eclipse occurs when the Moon passes between the Sun and Earth during a new moon.

Surface and environment: the Moon has plains called maria, rugged highlands, and numerous impact craters. It lacks a substantial atmosphere and has an extreme temperature range. Surface material, or regolith, is a mix of dust and broken rock. Evidence from recent missions indicates the presence of water ice in permanently shadowed polar regions.

Exploration and study: humanity has studied the Moon through telescopes, robotic spacecraft, and human missions. Notable programs include the Soviet Luna series and NASA’s Apollo program, which brought humans to the surface and returned lunar samples.