The Islamic calendar, also known as the Hijri calendar, is a lunar calendar consisting of 12 months in a year of 354 or 355 days. It is used primarily to determine the proper days of Islamic rituals and events, such as Ramadan and Hajj. Each month begins with the sighting of the new moon, making it about 10 to 12 days shorter than the Gregorian calendar. The Islamic calendar has significant cultural and religious importance in the Muslim world. It is used to mark important dates, including the birth of the Prophet Muhammad and the celebration of Eid al-Fitr and Eid al-Adha. The calendar's reliance on lunar cycles influences various aspects of daily life and religious observance for Muslims globally.