The Islamic calendar is lunar, like the Jewish calendar. Usually write as (A.H), it was used to fix religious observances and is based on a lunar cycle of 12 months of 29or 30 days. The Muslim year is thus 11 days shorter than the year according to the Gregorian calendar and months move forward accordingly.

In the Gregorian calendar, for example, April is always in the spring, but in the Muslim calendar all months move through all seasons in a 33-year cycle.

The Coptic calendar (A.M) is based on a solar cycle and consists of 12 months of 30 days and one month of 5 days. Every four years a sixth day is added to the shorter month. Many farmers, for planting and harvesting crops, use an adaptation of the Coptic calendar. The authorities of the Coptic Orthodox Church use it.
It consists of 12 months of 29 or 30 days each, for a total of 354 days. {1} Unlike its Jewish counterpart, however, the Islamic calendar has no corrective system to align it with the solar calendar. Thus the Islamic holidays do not always fall in the same season, and they occur earlier every year on the solar calendar.

The months of the Islamic calendar are as follows:
Θ Muharram
Θ Safr
Θ Rabi' al-Awwal (or Rabi I)
Θ Rabi' al-Thani (or Rabi II)
Θ Jumada al-Ula (or Jumada I)
Θ Jumada al-Thaniyya (or Jumada II)
Θ Rajab
Θ Sha'ban
Θ Ramadan
Θ Shawwal
Θ Dhu al-Qa'dah
Θ Dhu al-Hijjah