| Islam dates from the Hijra, or migration
from Mecca to Medina. Year 1, AH (Anno Hegira) corresponds to AD
622 or 622 CE, depending on the notation preferred (see Common
Era). It is a lunar calendar, but differs from other such
calendars (e.g. the Celtic calendar) in that it omits intercalary
months, being synchronized only with lunations, but not with the
solar year, resulting in years of either 354 or 355 days.
Therefore, Islamic dates cannot be converted to the usual CE/AD
dates simply by adding 622 years. Islamic holy days fall on fixed
dates of the lunar calendar, which means that they occur in
different seasons in different years in the Gregorian calendar. |
