Describe the features of Islamic Calendar. 

Islamic Calendar:

i. The Hijri era was established during the caliphate of Umar, with the first year falling in 622 CE. A date in the Hijri calendar is followed by the letters AH.
ii. The Hijri year is a lunar year of 354 days, 12 months (Muharram to Dhul Hijja) of 29 or 30 days. Each day begins at sunset and each month with the sighting of the crescent moon.
iii. The Hijri year is about 11 days shorter than the solar year. Therefore, none of the Islamic religious festivals, including the Ramazan fast, Id and hajj, corresponds in any way to seasons.
iv. There is no easy way to match the dates in the Hijri calendar with the dates in the Gregorian calendar (established by Pope Gregory XIII in 1582 CE).
vi. One can calculate the rough equivalents between the Islamic (H) and Gregorian Christian (C) years with the following formulae:

(H × 32 / 33) + 622 = C

(C – 622) × 33 / 32 = H