How are the phases of the moon caused?
Lunar phases are the result of our seeing the illuminated half of the Moon from different viewing geometries: They are not caused by shadows of the Earth on the Moon that occur during a lunar eclipse. The Moon exhibits different phases as the relative geometry of the Sun, Earth and Moon change, appearing as a full moon when the Sun and Moon are on opposite sides of the Earth, and becoming invisible as a new moon (also named dark moon) when they are on the same side. The phases of full moon and new moon are examples of syzygies, which occur when the Earth, Moon and Sun lie (approximately) in a straight line. The time between two full moons (or between successive occurrences of the same phase) is about 29.53 days (29 days, 12 hours, 44 minutes) on average. This synodic month is longer than the time it takes the Moon to make one orbit about the Earth with respect to the fixed stars (the sidereal month), which is about 27.32 days. This difference is caused by the fact that the Earth-Moon s
