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**

In non-leap years, a month would be 29.5 days

Need to add 11 days in each 30 year cycle to account for a month being longer than that

There are four different pattens of leap years in use for specifying which year in the cycle is a leap year.

These are designated as Type I, Type II, Type III, and Type IV

Type I: | 2, 5, 7, 10, 13, 15, 18, 21, 24, 26, 29 |

Type II: | 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, 29 |

Type III: | 2, 5, 8, 10, 13, 16, 19, 21, 24, 27, 29 |

Type IV: | 2, 5, 8, 11, 13, 16, 19, 21, 24, 26, 30 |

See Unicode CLDR Project for more details.

**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**

There are two different origins in use for 1 Muharram in the year 1.

These are designated as the astronomical origin and the civil one

Astronomical Origin:

1 Muharram year 1

= July 15, 622 (Julian Calendar)

= July 18, 622 (Gregorian Calendar)

= Ab 2, 4382 (Hebrew Calendar)

Civil 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