Synodic Month(glossary entry)
The length of the average interval of time between successive New Moons, or other fixed phases of the Moon as observed from Earth. About 29.5306 days.
- The actual interval between phases is not fixed. According to the Wikipedia the actual interval between New Moons can vary from about 29.27 to about 29.83 days. The variation in the interval between other phases may be slightly different.
- Because of the Moon's varying librations, a return to the same phase does not necessarily mean that the terminator is at the same position relative to the surface features.
- See the Wikipedia article for alternative definitions of the lunar month.