Muslims worldwide are currently in the midst of observing Ramadan. But just what, exactly, is Ramadan?

Ramadan is well known as the famous month-long fast of Islam. But Ramadan is actually also the proper name of a specific month in the Islamic calendar. Just as September is the name of the ninth month of the Western calendar, so Ramadan is the name of the ninth month of the Islamic calendar.

And yes, the calendar month of Ramadan is the month during which Muslims fast, from sunrise until sunset, every single day throughout the entire month. This is not considered optional, but is regarded as a compulsory religious duty (it is one of the so-called “Five Pillars of Islam,” each of which is incumbent upon all Muslims to abide by).

The month of September always runs 30 days. However, the month of Ramadan, like all months in the Islamic calendar, may run either 29 or 30 days. Islam follows a lunar calendar, according to which each successive new month does not technically begin until the first sighting of the crescent moon, just after sunset, on the last day of the previous month; the new month then runs for 29 or 30 days, depending upon when the next crescent moon is sighted (which in turn marks the beginning of the following month in the calendar).

This introduces a brief variable of uncertainty which makes it impossible to precisely predict, in advance, just exactly when a given month is going to end or begin; it also means that when months begin and end may vary slightly from location to location (from Muslim country to Muslim country).

This method of calculating months also means that the Islamic year ends up being 10 or 11 days shorter than a Western calendar year. In contrast to the Gregorian solar calendar followed by the West, with its 12 months of 365 days per year, Islam’s lunar calendar has 12 months of only 354 or 355 days per year. This means that its months are not locked in fixed synch with the seasons of the year, but instead fall 10 or 11 days earlier each year than they did in the previous year; as this creeping drift gradually accumulates year after year, Islamic calendar months slowly cycle their way back through each season, as the calendar years pile up.

Unlike the month of September, then, the month of Ramadan does not always fall at the beginning of autumn. Some years it might, making for a comparatively more pleasant or manageable fasting experience; in other years, however, Ramadan may fall at the peak of summer, with long and hot days making the daily fasting particularly challenging.

This is one of those years, with Ramadan currently falling during the Western calendar’s hot summer month of July. Last year (2011), Ramadan fell in August; this year (2012), Ramadan began at sunset on either Friday, July 20, or Saturday, July 21, depending on where you are (as described above, the beginning of any given month can vary, since it depends upon when the crescent moon is first spotted in the sky at any given location, or in any given Muslim country). And it began at sunset because Islam, like Judaism, regards sunset (not sunrise, and not midnight) as marking the “official start” of each new day.

What’s so special about the month of Ramadan? Well, it’s regarded by Muslims as the holiest month in the entire Islamic calendar. It was during the month of Ramadan that Muhammad first began to receive the divine revelations that would then continue for the remaining 23 years of his life, and which would subsequently be compiled by his followers as the holy Quran (or Koran), which Muslims revere as the actual, literal Word of God.

Fasting during Ramadan means no eating, no drinking (not even water), and no sexual relations from dawn till dusk. Fasting is not required of children until puberty, and health-based exceptions to the month-long fast are permitted for illness, old age, pregnancy, and similar recognized extenuating circumstances (although in some such cases, missed fast days must be made up later, where possible).

In addition to fasting, Ramadan is also a month of increased worship and prayer, reading and recitation of the Quran, religious devotion and spiritual reflection, self-examination and charity to the poor. It is said that the spiritual rewards reaped for such intensive extra efforts during Ramadan are greatly multiplied.

The daily fast is broken at sunset with an evening meal known as iftar. Often a community meal, iftar is frequently a chance for social gathering and religious fellowship throughout Ramadan.

So, depending upon where you are in the world (and depending when the first sighting occurred of the new crescent moon which signaled the start of the month), Ramadan began this year on or about July 20; it will run for 29 or 30 days, ending on or around August 18 (again, its actual length will depend upon when the new crescent moon is again sighted, marking the end of the month of Ramadan and the start of the following Islamic calendar month).

Each year, the entire month-long fast of Ramadan concludes with the festive annual celebration of Eid al-Fitr, a big fast-breaking feast and one of the Islamic calendar’s major holidays (it actually stretches over three days).

On July 20, President Barack Obama issued the following statement:

“On behalf of the American people, Michelle and I extend our warmest wishes to Muslim Americans, and Muslims around the world, at the start of Ramadan. For Muslims, Ramadan is a time of fasting, prayer, and reflection — a time of joy and celebration. It’s a time to cherish family, friends, and neighbors, and to help those in need. 

“This year, Ramadan holds special meaning for those citizens in the Middle East and North Africa who are courageously achieving democracy and self-determination, and for those who are still struggling to achieve their universal rights. The United States continues to stand with those who seek the chance to decide their own destiny, to live free from fear and violence, and to practice their faith freely. Here in the United States, Ramadan reminds us that Islam is part of the fabric of our Nation, and that from public service to business, from healthcare and science to the arts, Muslim Americans help strengthen our country and enrich our lives.

“Even as Ramadan holds profound meaning for the world’s 1.5 billion Muslims, it is also a reminder to people of all faiths of our common humanity and the commitment to justice, equality, and compassion shared by all great faiths. In that spirit, I wish Muslims across America and around the world a blessed month, and I look forward to again hosting an iftar dinner [the daily fast-breaking meal observed each evening during Ramadan] here at the White House. Ramadan Kareem.”

Ramadan Kareem means something like “Ramadan is generous.” This traditional expression reflects a sentiment of thanksgiving for the generous blessings that one has received, while also serving as a reminder that one should be generous in return.

Ramadan Kareem!