HEDJRAH (Hegirah), or, more fully, HEDJRAT AL-NABI, Arab. emigration (not flight, as commonly translated) of Mohammed (q.v.). The tribe of the Koreish having resolved to slay the new prophet, their kinsman, he secretly left Mecca on Sept. 13, 622 A.D., and repaired to Medina, where, partly from a feeling of jealousy towards Mecca, partly because his new doctrine had already found here many new adherents, he was so well received and so vigorously supported in the wars which he now began to wage against his adversaries, that the rise and progress of Mohammedanism was said to date in reality from the time of Mohammed's leaving Mecca. The Hedjrah, therefore, was made the starting-point of anew era—the Mohammedan (Tarikh Alhijrah)—by Caliph Omar, who, 639 or 640, with the aid of a Persian, Harmozan, instituted the new Moslem calendar. It does not, however, as is generally supposed, begin from the day of the flight itself, but from the first of the Moharram (the first month of the year) preceding it—a date corresponding to our July 10 or 16, 622 A.D.
The Mohammedan year, as a lunar year, is shorter than ours by 10 days 21 hour's and 141- seconds; and this circumstance renders the exact transfer of Mohammedan dates into dates of our own calendar a very difficult task- An elaborate method has been invented for that purpose by Meier; an easy, although not minutely accurate way of finding the vear, but not the month and the day, is by the deduction of 3 per cent from the given Mohammedan year, and the addition of 622 to the sum so obtained; e.g.. the year of the Hedjrah corresponding to 1809 A.D. being 1279, deduct 3 per cent, or about 39 = 1240, add 622 = 1862: