Phases of the Moon and its orbit around the Earth (2).
Suppose you are asked when the first quarter moon will rise,
when it will be overhead, and when it will set. Which side will be
illuminated?
•If it is first quarter, it has moved ¼ revolution around from the
new moon position, so it is at the top of the diagram.
•For a person standing on the earth, the moon would rise at
noon, be overhead at 6 pm, and
would set at midnight.
•It has to be the side towards the sun which is illuminated. Imagine yourself lying on the
ground at 6 pm, head north, right arm towards the west. That west (right) arm points towards the sun. That must be the side which is illuminated.
From our text: Horizons, by Seeds