The Lit Sides Of The Moon

This isn't anything breakthrough but here is something that I have never seen pointed out about the moon.

The phase of the moon that we see depends on the angle between the moon, the sun, and the earth. The visible moon is fully lit, known as full moon, when the earth is directly between the moon and the sun. The moon is not visible at all, known as new moon, when the moon is directly between the earth and the sun.

But at all other times, when the moon is partially lit, the lit portion must be either to the left or the right. Suppose that there is a crescent moon. The crescent can be either to the left, as in the first of the following illustrations, or to the right, as in the second illustration.

At the beginning of the lunar cycle, just after new moon, a crescent moon will appear in the western sky in the evening with the crescent to the right. Near the end of the lunar cycle, just before new moon, a crescent moon will appear in the eastern sky in the early morning with the crescent to the left. The lit side of the moon always faces toward the sun.

In the southern hemisphere, this is reversed. When looking toward the celestial equator, east is on the right and west is on the left. The lunar cycle, following new moon, begins with the crescent to the left and the cycle ends with the crescent to the right.

Most countries having the crescent moon on their flag have the crescent to the left. If the country is in the northern hemisphere, this means that this is the moon near the end of the lunar cycle and not the new moon.