Ramadan follows the Islamic calendar, which is based on the phases of the moon. Unlike the Gregorian solar calendar, which is widely used, the lunar calendar is about 11 days shorter. This disparity causes Ramadan to shift earlier by about 10 to 12 days each year relative to the Gregorian calendar, resulting in the observance of Ramadan at different times each year. The variability reflects the Islamic emphasis on the lunar calendar, aligning the holy month with the cycles of the moon and allowing Muslims around the world to experience Ramadan during various seasons over the years.