The Islamic, Muslim, or Hijri calendar (Arabic: التقويم الهجري at-taqwīm al-hijrī) is a lunar calendar consisting of 12 months in a year of 354 or 355 days. It is used in Muslim countries to determine the proper days of Islamic holidays and rituals, such as the annual period of fasting and the proper time for the pilgrimage to Mecca.
When we are told that there is a specific month and date, or day of the week, in the Islamic lunar calendar (or, infrequently, the Persian calendar) when something happened - for instance, "the Torah was revealed on 6 Ramadan" - this is because it is mentioned in narrations. Bihar al-Anwar includes many of these.
Mostly, we don't know the years when these things happened however.
It is generally held that, immediately prior to Islam, there was a lunar calendar in use in Mecca and Medina with twelve months and seven days per week; however, extra days were added each year so that it would match the solar calendar instead of being shorter than it (so the months would not move around the solar year). The Prophet (S) made the lunar calendar strictly lunar (without any extra days).
Additionally, years were referred to by events (such as "aam al-fil", or the Year of the Elephant), and this continued during the lifetime of the Prophet (S).
It generally held that, during the caliphate of 'Umar, at the suggestion of Imam 'Ali (A), the decision was made to count the years in the Islamic calendar beginning with the hijrah, instead of referring to the years by important events that happened to them, to make things easier for the expanding bureaucracy of the Arab-Muslim Empire, and thus it became the hijri calendar as we know it today. Some people hold that the Prophet (S) himself mandated the first year of the Islamic calendar be the year of migration, but this view is not very common.
Anyway, calendars can be quite complicated - people today often take them for granted because we have digital devices and communication by which we can all agree on the date and time, but for much of human history, it was a big challenge and responsibility to keep up with the calendar!
It starts on the previous day at sunset. Example:
| Saturday, February 13 = 1 Rajab |
1 Rajab starts on Friday at sunset and ends on Saturday at sunset.
Hope that helps!
This is an issue hotly debated among the Muslim scholars all over the world. I myself have been following the debate and also observing the scientific method for the last ten years. There are some aspects of the Islamic calendar which can be surely based on the scientific data; however, there still are issues which science has not been able to solve for us as yet.
At this stage, science is able to provide for us all the details about the movement and position of the moon around the earth: it can precisely predict when the birth of the new moon will occur, at what angle and at what location in relation to our earth.
We are also told by the experts that when and where the moon will be visible; and where it cannot not be sighted. For example, we are told that the first sighting of the crescent is possible only sixteen hours after the birth of the new moon. Experts can also give us a graph showing the location where the sighting will be possible.
For the last `idd, we were told that the sighting will only be possible for those who are west of the Atlantic Ocean. This was proved correct by the sighting of the moon in North America (I saw it myself in Dallas, TX) on Monday, the 19th of February, 1996.
I personally have confidence in such predictions based on the scientific data. BUT the problem lies in the following: (a) the 16 hour criterion by the experts is based on the observation done by the scientists in North America and Europe during the last 90 years. (b) reliable witnesses in the Middle East have claimed the sighting of the moon when the new moon was just 9 hours old.
When I look at this situation, I am faced with two possibilities: EITHER the sixteen hours criterion is valid only in the western hemisphere and that it might be possible to sight the moon of an age lesser than sixteen hours in desert areas where the atmosphere is much more clear. OR the reliable people in the Middle East have seen something but not the moon!
In conclusion, although I trust and have faith in the scientic data regarding the sighting of the crescent, we still need further confirmation from the scientific world about the universality of the sixteen hours criterion for moon sighting. When this criterion becomes universal, then it will be definitely possible for us to predict the beginning of the Islamic months well in advance. Insha Allah, we will reach to that stage of certainty sooner rather than later. Amin.