MUSLIM CALENDAR DESCRIPTION

Stephen P. Morse , San Francisco


Months

30 days: Muharram
29 days:  Safar
30 days:  Rabi' al-awwal (Rabi' I)
29 days:  Rabi' al-thani (Rabi' II)
30 days:  Jumada al-awwal (Jumada I)
29 days:  Jumada al-thani (Jumada II)
30 days:  Rajab
29 days:  Sha'aban
30 days:  Ramadan
29 days:  Shawwal
30 days:  Dhu al-Qi'day
29 days:  Dhu al-Hijjah (30 days in leap year)
 

Leap Years

Years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, 29 of each 30 year cycle
 

Days of Week

al-ahad: Sunday
al-ithnayn: Monday
ath-thulaathaa: Tuesday
al-arbia`aa': Wednesday
al-khamis: Thursday
al-jumu`a: Friday
as-sabt: Saturday
 

Origin

1 Muharram year 1
  = July 16, 622 (Julian Calendar)
  = July 19, 622 (Gregorian Calendar)
  = Ab 3, 4382 (Hebrew Calendar)
 

Muslim Calendar Month versus Jewish Calendar Month

Both the Jewish Calendar and the Muslim Calendar have the months tied to the moon.
So how do the lengths of a month in the two calendars compare?

The Jewish month is defined to be 29 days, 12 hours, 793 halaqim
   where a haliq (singular of halaqim) is 1/1080 of an hour
Based on that, the length of each year is dynamically adjusted so that the start of each year
   does not drift from the computed start of the first month in the year (Tishri)

The length of a Muslim month is computed as follows:
A normal year is 6 months of 30 days and 6 of 29 days for a total of 354 days
A leap year has an added day, and there are 11 leap years in every 30 year cycle
So 30 years = 354*30+11 = 10631 days
Since every year has 12 months, 30 years = 30*12 = 360 months
Therefore 360 months = 10631 days
which means
   1 month = 10631/360 days = 29 + 191/360 days
                = 29 days + (191/360)*24 hours = 29 days + 191/15 hours
               = 29 days + 12  11/15 hours = 29 days + 12 hours + (11/15)*1080 halaqim
               = 29 days + 12 hours + 792 halaqim

Conclusion: The Jewish Month and the Muslim Month differ by 1 haliq, or 3 1/3 seconds