A lunar calendar is based on the orbit of our Moon. The new moon (when you can’t see the Moon because it is aligned with the Sun) is usually the starting point to a lunar calendar. From there, the various phases seen from Earth include crescent, first quarter, and gibbous (these phases after a new moon are also labeled waxing, such as waxing crescent). When the entire face is seen, it is called a full moon; from there, the phases are seen “in reverse,” and are labeled waning, such as waning crescent. Overall, the entire moon cycle takes about 29.530589 days. This cycle was used by many early cultures as a natural calendar.