Eli5 the Islamic calendar. I’m unclear on how a 355 day calendar functioned


Happy Ramadan to all who observe it

Could someone Eli5 how a calendar that is less time than the time it takes the earth to travel around the sun used outside of a religious context?

I understand it’s connected to the stages of the moon and that the date for Ramadan moves in relation to the Gregorian calendar every year, was the ever a time when the Islamic calendar was used without the Gregorian calendar?

If so, how did that work logistically? I have a friend who was born during the month of Ramadan, and that year Ramandan was in the summer. Was it never an issue that the months don’t always corelate to seasons? Were seasons not really thing in the part of the world where the calendar was developed?

In: 5

from my humble knowledge, the Islamic calendar follows the lunar calendar. This calendar relies on phases of the moon to determine what day of the month it is ( to a certain accuracy using visual methods). So let us say if the sky had a full moon it meant that is the middle of the Islamic month.

It is actually unrelated to the Gregorian calendar(in the present time); as the former is related to the rotation of the moon around the earth, and the latter is related to the rotation of the Earth around the Sun.

so the Islamic calendar is a Lunar calendar and the Gregorian calendar is a Solar calendar.

Since we established that both calendars are different, the day your friend was born has both a gregorian and Islamic date and each is independent from each other.

Now for the uses of the Lunar calendar, people who are into stargazing usually pick days when the moon is not visible ( start of each lunar month) so the stars are more visible.

Considering Islam is about a thousand years older than the Gregorian calendar i’d say it is safe to say that the Islamic calendar was used without the Gregorian one.

Lunar calendars are fairly common, especially for religious purposes and different methods have been used to keep them aligned with solar calendars that are important for farming and travel, or people have just let them drift relative to the seasons.

> was the ever a time when the Islamic calendar was used without the Gregorian calendar?

Strictly speaking, yes, since the adoption of the Islamic calendar predated the adoption of the Gregorian. But the Gregorian was a minor tweak on the much older Julian calendar, with a new way of choosing leap years. But the Islamic was also a tweak on an older calendar, with a new Year 1 and no extra months. So … [shrug glyph].

The designers of all these calendars understood that the solar year is not an integral number of either days or lunar months long; they dealt with that in various ways: Give up trying to match the length of the calendar month to the lunar month; give up trying to match the length of the calendar year to the solar year; whatever.

> In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, with Syriac month-names used in the Levant and Mesopotamia (Iraq, Syria, Jordan, Lebanon and Palestine) but the religious calendar is the Hijri one.


Being desert nomads, the earliest Muslims had no need to match the solar year with their calendar, so a simple 12-month year didn’t cause trouble. This may also have been motivated by a desire to distinguish themselves from the Jews, whose calendar adds a 13th month to some years to maintain the link to the solar year.

This caused some serious trouble in the Ottoman Empire, which had income based on the solar year but expenditures based on the Islamic year. This was finally solved in 1839 by adopting a variant of the Julian calendar.

Lunar and solar calendars were both used in the Middle East (eg the date of the crucifixion is 15 Nisan – the 3rd lunar month of the year in the Babylonian calendar. They were reconciled by adding an extra month when needed – but the solar calendar was used for agriculture. The Islamic calendar is a purely lunar calendar, and does not adjust, so cycles around the solar year every 33 years. For non-religious purposes people use a version of the Gregorian calendar or the solar Persian calendar.