Frequently Asked Questions

Q. Why does the full moon always rise at sunset?
A. This is a consequence of the geometry of the sun-earth-moon system. When the moon is full, it is facing directly at the sun, so that the reflected light fills the disk. For this to be true the moon must be roughly in a line with the sun and earth, so that they are in opposite directions in the sky (astronomers refer to this as "opposition"). Consequently, at sunset, the moon is in the opposite direction in the sky, i.e. on the opposing horizon, and rising just as the sun is setting. See also http://en.wikipedia.org/wiki/Opposition_(astronomy) .