The islamic calendar was first started by the second Khalifa (Muslim Ruler) Omar Ibn-Al-Khattab. It starts with the Prophet Muhammed (SAW)'s migration from Mecca to Medina. The islamic calendar is basically a lunar calendar, whose 29 or 30 days are determined by the moon's motion around the Earth. The islamic calendar is not a fixed calendar (i.e the islamic months fall at different times of the seasons each year) when compared to the Gregorian calendar which is solar based calendar. The number of months in the islamic calendar is twelve and the names of these months are as follows: Muharram, Safar, Rabi' Al-Awwal, Rabi' AthThaani, Jumada Al-Oolaa, Jumada AthThaaniya, Rajab, Sha'baan, Ramadhan, Shawaal, Thool-Qi'da, and Thool-Hijja.