moonlight

Moonlight is the illumination of Earth's surface by sunlight reflected off the Moon. The Moon itself does not emit light; its brightness comes from solar radiation that bounces off its surface and reaches Earth after diffusion and scattering. The amount of moonlight visible depends primarily on the Moon’s phase and distance: it is brightest during a full Moon when the Sun, Moon, and Earth are aligned with the Moon opposite the Sun. The brightness also varies with the Moon’s distance from Earth (perigee makes a slightly brighter Moon) and with atmospheric conditions such as transparency and aerosols.

Photometrically, the full Moon has an apparent visual magnitude of about −12.7 and can illuminate the ground to roughly 0.1–0.3 lux under favorable skies. A new Moon provides far less light. Moonlight has a broad spectrum similar to sunlight, giving it a white appearance; slight color shifts toward blue can occur in very clear air, while a warm yellowish tint is sometimes noted near the horizon due to atmospheric scattering and dust.

The Moon’s average reflectance, or albedo, is about 0.12, meaning roughly 12% of incident sunlight is reflected. The reflection is diffuse rather than directional. Earthshine—sunlight reflected from Earth onto the Moon and then back to Earth—can render the Moon’s dark hemisphere faintly visible under certain conditions.

Moonlight influences some ecological and human activities and has long been a subject of study in astronomy and photography.