The Muslim dates are in the Islamic calendar extended back in time. The Western dates are in the Julian calendar. The Hijra is celebrated annually on 8 Rabi' I, about 66 days after 1 Muharram, the first day of the Muslim year. Many writers confuse the first day of the year of the Hijra with the Hijra itself, erroneously stating that the Hijra occurred on 1 Muharram AH 1 or 16 July 622.