Question

Why do the sun, the moon, and the earth not lie in one and the same line on every full moon and new moon day?

Answer 1

1. The orbital paths of the earth around the sun and that of the moon around the earth are not in the same plane.
2. The moon's revolutionary orbit makes an angle of about 5° with that of the earth. Therefore, the sun, the moon, and the earth do not lie in one and the same line on every full moon day and new moon day.