THE THE MOONMOON

From any location on the Earth, the Moon From any location on the Earth, the Moon appears to be a circular disk which, at any appears to be a circular disk which, at any specific time, is illuminated to some specific time, is illuminated to some degree by direct sunlight. Like the Earth, degree by direct sunlight. Like the Earth, the Moon is a sphere which is always half the Moon is a sphere which is always half illuminated by the Sun, but as the Moon illuminated by the Sun, but as the Moon orbits the Earth we get to see more or less orbits the Earth we get to see more or less of the illuminated half.of the illuminated half.

During each lunar orbit (a lunar month), During each lunar orbit (a lunar month), we see the Moon's appearance change we see the Moon's appearance change from from notnot visibly illuminated through visibly illuminated through partiallypartially illuminated to illuminated to fullyfully illuminated, illuminated, then back through then back through partiallypartially illuminated to illuminated to notnot illuminated again. Although this cycle illuminated again. Although this cycle is a continuous process, there are eight is a continuous process, there are eight distinct, traditionally recognized stages, distinct, traditionally recognized stages, called phases. called phases.

The phases designate both the degree to The phases designate both the degree to which the Moon is illuminated and the which the Moon is illuminated and the geometric appearance of the illuminated geometric appearance of the illuminated part. These phases of the Moon, in the part. These phases of the Moon, in the sequence of their occurrence (starting sequence of their occurrence (starting from New Moon), are listed below.from New Moon), are listed below.

1. New Moon1. New Moon

The Moon's The Moon's unilluminated side is unilluminated side is facing the Earth. The facing the Earth. The Moon is not visible Moon is not visible (except during a solar (except during a solar eclipse).eclipse).

2. Waxing Crescent2. Waxing Crescent

The Moon appears to The Moon appears to be partly but less than be partly but less than one-half illuminated one-half illuminated by direct sunlight. The by direct sunlight. The fraction of the Moon's fraction of the Moon's disk that is illuminated disk that is illuminated is increasing.is increasing.

3. First Quarter3. First Quarter

One-half of the Moon One-half of the Moon appears to be appears to be illuminated by direct illuminated by direct sunlight. The fraction sunlight. The fraction of the Moon's disk of the Moon's disk that is illuminated is that is illuminated is increasing.increasing.

4. Waxing Gibbous4. Waxing Gibbous

The Moon appears to The Moon appears to be more than one-half be more than one-half but not fully but not fully illuminated by direct illuminated by direct sunlight. The fraction sunlight. The fraction of the Moon's disk of the Moon's disk that is illuminated is that is illuminated is increasing.increasing.

5. Full Moon5. Full Moon

The Moon's The Moon's illuminated side is illuminated side is facing the Earth. The facing the Earth. The Moon appears to be Moon appears to be completely illuminated completely illuminated by direct sunlightby direct sunlight

6. Waning Gibbous6. Waning Gibbous

The Moon appears to The Moon appears to be more than one-half be more than one-half but not fully but not fully illuminated by direct illuminated by direct sunlight. The fraction sunlight. The fraction of the Moon's disk of the Moon's disk that is illuminated is that is illuminated is decreasing.decreasing.

7. Last Quarter7. Last Quarter

One-half of the Moon One-half of the Moon appears to be appears to be illuminated by direct illuminated by direct sunlight. The fraction sunlight. The fraction of the Moon's disk of the Moon's disk that is illuminated is that is illuminated is decreasing.decreasing.

8. Waning Crescent8. Waning Crescent

The Moon appears to The Moon appears to be partly but less than be partly but less than one-half illuminated one-half illuminated by direct sunlight. The by direct sunlight. The fraction of the Moon's fraction of the Moon's disk that is illuminated disk that is illuminated is decreasing.is decreasing.