The phases of the moon are about 29½ days long. (http://en.wikipedia.org/wiki/Moon http://en.wikipedia.org/wiki/Moon and see the synodic period (quoted to a te

The phases of the moon are about 29½ days long. (http://en.wikipedia.org/wiki/Moon http://en.wikipedia.org/wiki/Moon and see the synodic period (quoted to a tenth of a second even though full moon to full moon can vary by about ¼ day either way).)