Anno Domini Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! == No year zero: start and end of a century == {{Further|Year zero|Astronomical year numbering|Millennium|Century|Decade}} In the AD year numbering system, whether applied to the [[Julian calendar|Julian]] or [[Gregorian calendar]]s, AD 1 is immediately preceded by 1 BC, with nothing in between them (there was no [[year zero]]). There are debates as to whether a new decade, century, or millennium begins on a year ending in zero or one.<ref name="Teresi1997" /> For computational reasons, [[astronomical year numbering]] and the [[ISO 8601]] standard designate years so that AD 1 = year 1, 1 BC = year 0, 2 BC = year β1, etc.{{efn|To convert from a year BC to [[astronomical year numbering]], reduce the absolute value of the year by 1, and prefix it with a negative sign (unless the result is zero). For years AD, omit the AD and prefix the number with a plus sign (plus sign is optional if it is clear from the context that the year is after the year 0).<ref>Doggett, 1992, p. 579</ref>}} 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. Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Christianpedia:Copyrights for details). Do not submit copyrighted work without permission! Cancel Editing help (opens in new window) Discuss this page