My friends and I have an annual challenge where we try to figure out when Ramadan begins, as it changes every year. Officially, it starts when a couple of countries say they spotted the crescent moon, which can get a bit competitive. The Islamic calendar system is based on the moon cycle, not the sun’s, and each month begins with a waxing crescent. This complete cycle takes 29 to 30 days, and that’s the reason why we fast from before sunrise to sunset for that length of time.

Ramadan is the ninth month of the Islamic year. Since the lunar months are shorter than the solar months we’re used to, the year is shorter too, and that means Ramadan and other Islamic holidays are about 10 days earlier each year. This year, the year 1444, Ramadan began on March 23rd after multiple sightings of the waxing crescent a day earlier.

The announcement not only set off the holy month of fasting, but it’s also a time when Muslims dedicate more time to self-reflection, prayer, and charity. To mark off the end of the month or the holiday, Eid al-Fitr, we’ll all be back to where we started – trying to spot the crescent moon again.