Although the Arabic calendar had been widespread among some of the
nations including the Arabs long before Islam’s advent, but after this
historic event turned out to be the official historical calendar which at the
moment, is the common calendar among billions of Muslims. The Lunar
year (The Arabic Calendar) has been called the crescent year as well,
because the moon (while being crescent) starts circling around the earth,
which takes 29 days, 12 hours and 43 minutes, therefore the Lunar year
lasts 354 days.
The Lunar months are: Moharram, Safar, Rabi I ,Rabi II, Jumada I,
Jumada II, Rajab, Sha’ ban, Ramadhan, Shawwal, Zu’l-Qa’dih, Zu’l- Hijjah.
The Muslims have considered the Holy Prophet’s vital immigration from Mecca
to Medina as the historical origin of the Lunar year, the event which had
occurred so long ago and now after passing so many years we call this as
the Lunar Hijra calendar.