Moon Phases

Why the Moon appears to change shape each night

The Moon does not emit its own light — it reflects sunlight. As the Moon orbits Earth once every 29.5 days, we see different portions of its lit side from Earth, creating the phases. New Moon: Moon is between Earth and Sun — we see the unlit side (dark). Waxing Crescent: small sliver visible. First Quarter: half the Moon is lit (right half). Waxing Gibbous: more than half lit. Full Moon: Moon is opposite the Sun — we see the fully lit side. Then the cycle reverses: Waning Gibbous, Last Quarter, Waning Crescent, back to New Moon. Lunar eclipses occur when Earth's shadow falls on the full Moon; solar eclipses when the new Moon covers the Sun.