Third Quarter


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Day of Lunar Cycle


Synodic Position

Western Quadrature

Angle of Sun-Earth-Moon

The Moon lies exactly 90° ahead or to the west of the Sun

Illuminated side

Half-turned away from Earth

Near side

Half dark, half light (often called a "half moon")

Overlap between near side and illuminated side


Proportion of whole Moon that is both illuminated and near

25% (therefore a "quarter moon").
Note: This phase is called the "Third quarter" because the Moon has traveled three-fourths of its way through the lunar cycle.

Which part of the near side is illuminated?

Eastward or Left side (facing south)

Where visible at sunset?

Not visible; near one's nadir.

Where visible at midnight?

Rising in the east.

Where visible at sunrise?

High overhead in the south, crossing the meridian

Where visible at noon?

Setting in the west.

Meridian Transit


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