The second system is based on the revolution of the moon around the Earth. The time interval from one new moon to the next (called “lunation”) is 29 days, 12 hours, 44 minutes, and 2.8 seconds. A 12-month calendar—with each month having a value of 29.5 days—results in a year consisting of 354 days, which is 11 days short of the solar year. The Islamic calendar is completely lunar in nature. It is composed of 12 months of 29 or 30 days each.
