Unlike the Christian (Gregorian) calendar used in most Western countries—which is based on the solar cycle—the Islamic calendar follows a lunar structure, determining the length of its months by the phases of the Moon.

Like the Gregorian calendar, the Islamic calendar comprises 12 months, which are:

• Muharram
• Safar
• Rabbi Al-Awwal
• Rabbi Al-Thani
• Jumad Al-Ula
• Jumad Al-Ukhra
• Rajab
• Sha’ban
• Ramadhan
• Shawwal
• Dhul Qa’dah
• Dhul Hijjah

Several of these months hold significant religious importance. Ramadhan, perhaps the most well-known, is the month during which Muslims fast daily from dawn to sunset. Dhul Hijjah is also notable, as it marks the time of the annual pilgrimage to Makkah, known as Hajj.

The Islamic calendar does not begin with the birth of the Prophet Muhammad, as commonly misunderstood, but rather with the Hijrah—the migration of the Prophet (PBUH) and his followers from Makkah to Madinah in 622 CE.

Because it follows the lunar cycle, the Islamic year is approximately 10 days shorter than the Gregorian year, causing Islamic months to shift backward through the seasons over time.

Many of these months have special religious significance.

Ramadhan, for example, perhaps the most famous month of the calendar, is
the month during which Muslims all over the world fast from sunrise to sunset.

Dhul Hijjah is also important as this is the month in which Muslims make
the annual pilgrimage to Makkah, known as Hajj.

The Islamic calendar dates back not to the birth of the Prophet
Muhammad, as mistakenly believed by many, but to the year of the Hijrah, or
migration to the city of Madinah from Makkah by the Prophet Muhammad ^(PBUH)
and his followers in 622 CE.

As the Islamic
calendar runs by the Moon, its year is consequently around 10 days shorter than
the Gregorian calendar year, so the months drift backwards through the seasons
each year.