The Islamic calendar is lunar, which means it's based on the phases of the moon. It is either 354 or 355 days long, and began in the year 622 CE when the Prophet Muhammad migrated from Mecca to...
The Gregorian calendar, used by most countries in the western world, was initially decreed by Pope Gregory XIII on 24 February 1582. The Gregorian calendar was first proposed by Aloysius Lilius...