The 'age' is the distance in degrees (from 0 to 360) that the moon has traversed in its orbit since it was new. The phase is percentage of the moons' face which is currently lit, (i.e., it is 100% at full and 0% at new). If the phase is currently increasing the moon is said to be waxing and if it is decreasing it is said to be waning.

The first symbolic system is believed to be a bone from the Paleolithic with 28 scratches on it indicating a knowledge of the lunar cycle. The moon is also the basis of many of the calendars of the world, and is key to Jewish, Islamic, and Christian liturgical calendars; the exact dates of Rosh Hashana, Ramadan and Easter all depend on lunar events which vary from year to year. In some cases, such as the Islamic calendar, a particular phase of the moon must actually be observed at a given location.