Weather Insider: Astronomical calendars

There are a number of different astronomical calendars. They are lunar calendars, lunisolar calendars, and solar calendars. Lunar Calendars are based solely on the cycles of the moon. Since one lunar month is 29.5 days, a lunar year is about 354 days.

A lunisolar calendar is still based on the moon but adds extra time in the form of leap months to align the calendar with the solar year. Lastly, there is a solar calendar. This is the calendar most widely used today and is based on the Earth's orbit around the sun.