2 BC = year −1, etc. In common usage, ancient dates are expressed in the Julian calendar, but ISO 8601 uses the Gregorian calendar and astronomers may use a variety of time scales depending on the application. Thus dates using the year 0 or negative years may require further investigation before being converted to BC or AD. See also Before Present Holocene calendar Notes References Citations Sources Bede. (731). Historiam ecclesiasticam gentis Anglorum . Retrieved 2007-12-07. Corrected reprinting of original 1999 edition. (despite beginning with 2, it is English) Declercq, G. "Dionysius Exiguus and the Introduction of the Christian Era". Sacris Erudiri 41 (2002): 165–246. An annotated version of part of Anno Domini. Doggett. (1992). "Calendars" (Ch. 12), in P. Kenneth Seidelmann (Ed.) Explanatory supplement to the astronomical almanac. Sausalito, CA: University Science Books. . Patrick, J. (1908). "General Chronology" . In The Catholic Encyclopedia. New York: Robert Appleton Company. Retrieved 2008-07-16 from New Advent: Catholic Encyclopedia: General Chronology External links Calendar Converter 6th-century Christianity Calendar eras Christian terminology Chronology Latin religious words and phrases Timelines of Christianity