- published: 27 Mar 2013
- views: 1651298
Year zero does not exist in the Anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year 1 BC is followed by AD 1. However, there is a year zero in astronomical year numbering (where it coincides with the Julian year 1 BC) and in ISO 8601:2004 (where it coincides with the Gregorian year 1 BC) as well as in all Buddhist and Hindu calendars.
The absence of a year 0 leads to some confusion concerning the boundaries of longer decimal intervals, such as decades and centuries. For example, the third millennium of the Gregorian calendar began on Monday, 1 January 2001, rather than the widely celebrated Saturday, 1 January 2000. Likewise, the 20th century began on 1 January 1901.
This rule arose because the Gregorian calendar begins with a year 1 instead of 0. Cardinal and ordinal numbering of years is therefore identical: The year 10 is the tenth year of the calendar and the end of the first decade. The year 11 is the first year of the second decade, and so on. In spite of this rule, years ending in 0, rather than 1, are commonly perceived as marking the beginning of a new decade, century, or millennium. Decades, however, are more used as a collective term (e.g. the 1930s) rather than a periodical term (e.g. 1930–1939).