Islamic months are part of the lunar calendar used by Muslims around the world. Each month begins with the sighting of the new moon and lasts either 29 or 30 days. There are twelve months in total, including significant ones like Ramadan, a month of fasting, and Dhu al-Hijjah, which includes the Hajj pilgrimage. The Islamic calendar is about 10 to 12 days shorter than the Gregorian calendar, causing Islamic months to shift each year. This means that Islamic holidays and observances, such as Eid al-Fitr and Eid al-Adha, occur on different dates annually in the Gregorian calendar.