What are the phases of the Moon?

The angle between the Sun and the Moon in the sky determines how much of the Moon people on Earth can see, or which “phase” the Moon is in. There are eight lunar phases during which, from Earth’s perspective, the Moon is illuminated by the Sun in different amounts. The new moon occurs when the Moon is between the Sun and Earth, so we see the face blocked from sunlight. A waxing crescent occurs when one-fourth of the face of the Moon is illuminated by the Sun, and the first quarter is when the Moon is half-illuminated. At this point, the Moon is not in line with the Sun and Earth but is perpendicular to that line. Then comes the waxing gibbous phase, when three-fourths of the Moon’s face is illuminated. A full moon occurs once the Moon’s face is as close to being fully illuminated by the Sun as it can be. At this point, people on Earth see the Moon as a complete circle. The next phase is the waning gibbous, when three-fourths of the Moon’s face is illuminated but the amount of sunlight is decreasing. The last quarter phase occurs when sunlight illuminates the other half of the face of the Moon. Once the Moon reaches the waning crescent phase, one-quarter of the Moon’s face appears to receive the Sun’s light. And then the cycle repeats, every 29½ days. For centuries farmers’ almanacs have used the Moon’s phases as a guiding light metaphorically as well as literally. The new and waxing phases were traditionally considered to be fertile and wet times for farming, and the full and waning phases dry and barren. Even before the first written language, the Moon was used as an early calendar. Etchings and cave paintings hint at ancient peoples’ ability to recognize the repetitive and reliable cycles of the Moon.