For most of the week, the Muslim world will be celebrating Eid al-Adha. Here are ten facts you might not have known about the festival.

1. Eid al-Adha, also known as Eid al-Kabir or Eid al-Qurban, is an Islamic festival to commemorate Abraham’s willingness to follow God’s command to sacrifice his only son, Ishmael. Moments before the sacrifice, God revealed to Abraham that His command was merely a test of Abraham’s devotion, and that he doesn’t need to sacrifice Ishmael anymore. Instead, he was asked to sacrifice a sheep.
2. Eid al-Adha is the Festival of Sacrifice in English.
3. According to the Islamic calendar, which is based on the lunar cycle, Eid al-Adha begins on the tenth of Dhu’l-Hijja, the twelfth month of the Islamic year. However, the Gregorian calendar, which is widely used across the world, is based on the solar cycle. Therefore, the Eid al-Adha moves 11 days back on the Gregorian calendar every year.
4. Eid al-Adha is between a two and four day celebration, depending on the country.
5. The Eid al-Adha dates are confirmed only if reputable moon-sighting committees in the Islamic world announce they have spotted the new moon with the naked eye.
6. A Muslim must recite ‘tusmiya’ before sacrificing a sheep and make sure it is of a certain age and in good health. When slaughtering sheep, a Muslim must ensure the sacrifice meets Islamic standards, and the meat is ‘halal’. The slaughterer must cut a deep incision into the animal’s neck, severing the jugular veins and carotid arteries.
7. The meat from the sacrifice is divided into three portions: a third for the family, a third to friends, and a third donated to the poor.
8. It is customary for Muslims to mark the occasion by giving away gifts, wearing new clothes, and visiting family and friends. Older family members usually give children money in Eid al-Adha.
9. In the period around Eid al-Adha, many Muslims travel to Mecca for the Hajj pilgrimage (one of the five pillars of Islam). The Eid begins the day after Muslims on the Hajj descend from Mount Arafat.
10. On the first morning of Eid al-Adha, Muslims around the world attend morning prayers at their local mosques. It has been said that it is better for to take a different route back home then route first taken to go to the mosque.