Lunar phases are the result of our eyes seeing the illuminated half of the Moon from different viewing geometries. 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 when they are on the same side. The time between two full moons (or between successive occurrences of the same phase) is called a synodic month and is about 29.53 days long (29 days, 12 hours, 44 minutes) on average.