Islamic Calendar Year: Lunar, Solar, and Gregorian

Calendar Year: Lunar, Solar, and Gregorian

The calendar year is used to organize time, measure its passage, and synchronize human activities with natural phenomena. In Islam, the calendar year is based on lunar years, which consist of twelve months and approximately 354 days. This lunar year differs from both the solar and Gregorian calendar years.

Lunar Year

In the Islamic lunar calendar, each month starts when the first sliver of the waxing crescent is sighted after sunset. A lunar year has only 29 or 30 days, depending on whether the month begins immediately after a full moon or a new moon. This results in the following approximate durations per year:

• Number of years per century: 30 x 365 + 1 = 11,151 years
• Number of days per 400 years: 365 x 400 + 0.25 x 1,461 = 146,100 days
• Number of leap years per 400 years: 0.25 x 1,461 = 365.25

Solar and Gregorian Years

A solar year is defined as the period it takes for Earth to orbit around the Sun once, which is approximately 365.2425 days. However, this is slightly shorter than the lunar year, so two solar years may not correspond exactly to two lunations. Nevertheless, the number of years needed for the sun's position to return to almost the same place on the sky background as observed in the middle of January 1 AD can be expressed by multiplying the number of years between two dates by the ratio of the solar to the sidereal year length:

• 2592 years / (365.2425 / 365.25) ≈ 30.62965

Gregorian years are based on the solar year, using leap years to synchronize with lunations. There are 14 leap years out of every 400.

Islamic Calendar Years

The Islamic calendar differs from the Gregorian in several ways. While both calendars have leap years, there are significant differences between them. In the Gregorian calendar, the number of days in February varies between 28 and 29 depending on whether it is a leap year. However, in the Islamic calendar, February has only 29 days in a leap year. Additionally, while February in the Gregorian calendar always occurs before March, its position relative to other months changes throughout the Islamic calendar. This creates unique challenges when comparing dates across different years within the Islamic calendar.

Months and Their Durations

There are twelve months in the Islamic calendar, which align approximately with the seasons. Each month begins with the sighting of the new moon. The length of each month can vary slightly due to the lunar cycle's period being approximately 29.5 days long.

Month Lengths and Durations

The lengths of months are variable because they begin with a new moon sighting. The average duration of each month is about 29.5 days, but some months have 29 days and others have 30 days.

Rabi' al-awwal and Safar

Rabi' al-awwal has between 29 and 30 days, while Safar always has 29 days. The average duration of Rabi' al-awwal is about 29.5 days, and the average duration of Safar is about 29.25 days.

Muharram and Rabī' ath-thānī

Muharram has between 29 and 30 days, while Rabī' ath-thānī always has 29 days. The average duration of Muharram is about 29.5 days, and the average duration of Rabī' ath-thānī is about 29.25 days.

Jumādā al-ūlā and Jumādā al-akhirah

Jumādā al-ūlā has between 29 and 30 days, while Jumādā al-akhirah always has 30 days. The average duration of Jumādā al-ūlā is about 29.5 days, and the average duration of Jumādā al-akhirah is about 29.5 days.

Rajab

Rajab has between 29 and 30 days. The average duration of Rajab is about 29.5 days.

Shawwāl

Shawwāl has between 29 and 30 days. The average duration of Shawwāl is about 29.5 days.

Dhū al-Qa'dah and Dhū al-Hijjah

Dhū al-Qa'dah has between 29 and 30 days, while Dhū al-Hijjah always has 30 days. The average duration of Dhū al-Qa'dah is about 29.5 days, and the average duration of Dhū al-Hijjah is about 29.5 days.

Dhū al-Hijjah

The duration of Dhū al-Hijjah varies from 29 to 30 days. The average duration of Dhū al-Hijjah is about 29.5 days.

Conclusion

The Islamic calendar year is based on lunar months, which have variable lengths due to the lunar cycle's period being approximately 29.5 days long. This results in months having between 29 and 30 days, with an average duration of about 29.5 days. The Islamic calendar year is approximately 354 days long, which is shorter than the solar and Gregorian calendar years.