maanfase

A maanfase, in Dutch, refers to the phase of the Moon—the varying appearance of the Moon's illuminated portion as seen from Earth. The sequence results from the changing relative positions of the Sun, Moon, and Earth. The Moon orbits Earth about once every 27.3 days (sidereal month), but the cycle of phases, from new moon to new moon, takes about 29.5 days (the synodic month) because Earth orbits the Sun.

During the cycle, the Moon passes through eight commonly named phases: new moon (when the Moon is between Earth and Sun and the illuminated side faces away from Earth), waxing crescent, first quarter (half-illuminated, increasing), waxing gibbous, full moon (fully illuminated as the Sun and Moon are on opposite sides of Earth), waning gibbous, last quarter (or third quarter), and waning crescent. The terms waxing and waning describe whether the visible illuminated portion is increasing or decreasing.

The appearance is determined by the angle between Sun, Moon, and Earth; not by Earth's shadow except during lunar eclipses, which occur only near full moon when Earth lies between Sun and Moon. Eclipses are relatively rare compared with normal phases.

Observationally, the phase is roughly the same for observers around the world, though the Moon's orientation to the horizon varies with latitude. Moon phases influence natural phenomena such as tides, and have been used in calendars and timekeeping across cultures.