Ramadan is one of the most significant months—the ninth—of the Muslim calendar. It is believed that this is when the Holy Quran, the book that guides those who follow Islam, was sent to earth from heaven. Ramadan’s date varies according to the cycles of the moon, which periodically puts the start of the holiday in December for several years running, but can occur any time during the year, including summer.

Also known as the holiest of months, Muslims use Ramadan as a time to worship and to renew their faith. To help them do that without the interferences of everyday life, they will observe a fast during daylight hours, during which they will refrain from eating and drinking and other activities, such as smoking. It’s also important during this time to watch one’s behavior: to avoid lying or gossiping or being angry or jealous. The focus is on being pure in thought, word, and deed.

The fast begins at daylight—defined as the earliest time of day in which you can distinguish a white thread from a black one—and can be broken with a meal called the iftar as soon as it is night. While the fast can be challenging in countries near the equator, where night and day are roughly equal, it can be even more difficult in northern countries where nights can be much longer than the days, depending on the time of year. In this case, the fasting schedule of other countries is often adopted.

The end of Ramadan is celebrated with a three-day festival to break the fast, called Eid ul-Fitr. It’s a time to gather with family and friends, to eat and pray together, and to recognize those less fortunate with gifts of food. In an interesting echo of traditions from other cultures, new clothes are often worn during this festival—once again symbolizing a rebirth.