\begin{definition}[Definition:Calendar/Muslim]
The '''Muslim calendar''' is a calendar whose period is based on $12$ full cycles of phases of the moon.
Each Muslim year lasts either $354$ or $355$ days, depending on precisely when the relevant new moons happen
The years are numbered from the year when {{WP|Muhammad|Muhammad}} and his followers migrated from {{WP|Mecca|Mecca}} to {{WP|Medina|Medina}} in $622 \, \text{A.D}$ by the Julian calendar.
Years are denoted with the suffix $\text{A.H.}$, meaning '''Anno Hegirae''', literally '''in the year of the Hejira'''.
The start and end of the Muslim year are $10$ to $12$ days earlier every civil year.
The $354$ or $355$ days in the Muslim year are divided into $12$ approximately equal sections called months, each either $29$ or $30$ days, depending on the phases of the moon.
They are assigned both names and index numbers:
{{begin-eqn}}
{{eqn | l = 1:
      | o = 
      | c = Muḥarram
}}
{{eqn | l = 2:
      | o = 
      | c = Ṣafar
}}
{{eqn | l = 3:
      | o = 
      | c = Rabī‘ al-awwal
}}
{{eqn | l = 4:
      | o = 
      | c = Rabī‘ ath-thānī
}}
{{eqn | l = 5:
      | o = 
      | c = Jumādá al-ūlá
}}
{{eqn | l = 6:
      | o = 
      | c = Jumādá al-ākhirah
}}
{{eqn | l = 7:
      | o = 
      | c = Rajab
}}
{{eqn | l = 8:
      | o = 
      | c = Sha‘bān
}}
{{eqn | l = 9:
      | o = 
      | c = Ramaḍān
}}
{{eqn | l = 10:
      | o = 
      | c = Shawwāl
}}
{{eqn | l = 11:
      | o = 
      | c = Dhū al-Qa‘dah
}}
{{eqn | l = 12:
      | o = 
      | c = Dhū al-Ḥijjah
}}
{{end-eqn}}
\end{definition}