section_path: Year numbering
section_name: Year numbering
paragraph_text: Year numbering
  
  A calendar era assigns a cardinal number to each sequential year, using a reference event in the past (called the epoch) as the beginning of the era.
  
  The Gregorian calendar era is the world's most widely used civil calendar. Its epoch is a 6th century estimate of the date of birth of Jesus of Nazareth. Two notations are used to indicate year numbering in the Gregorian calendar: the Christian " Anno Domini " (meaning "in the year of the Lord"), abbreviated AD; and " Common Era ", abbreviated CE, preferred by many of other faiths and none. Year numbers are based on inclusive counting, so that there is no "year zero". Years before the epoch are abbreviated BC for Before Christ or BCE for Before the Common Era. In Astronomical year numbering, positive numbers indicate years AD/CE, the number 0 designates 1 BC/BCE, −1 designates 2 BC/BCE, and so on.
  
  Other eras include that of Ancient Rome, Ab Urbe Condita ("from the foundation of the city), abbreviated AUC; Anno Mundi ("year of the world"), used for the Hebrew calendar and abbreviated AM; and the Japanese imperial eras. The Islamic Hijri year, (year of the Hijrah, Anno Hegirae abbreviated AH), is a lunar calendar of twelve lunar months and thus is shorter than a solar year.