Astronomical year numbering

Astronomical year numbering is based on AD (Anno Domini)/CE (Common Era) year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0 and the years before that are designated with a minus sign '−'. The era designations BC (Before Christ)/BCE (Before Common Era) are dropped. So the year 1 BC/BCE is numbered 0, the year 2 BC is numbered −1, and in general the year "n" BC/BCE is numbered (1−"n"). The numbers of AD/CE years are not changed, but AD/CE is not used, being replaced by either no sign or a positive sign; thus in general "n" AD/CE is simply (+) "n". For normal calculation a number zero is often needed, here most notably when calculating the number of years in a period that spans the epoch; the end years need only be subtracted from each other.

The system is so named due to its use in astronomy. Few other disciplines outside history deal with the time before year 1, exceptions being dendrochronology, archaeology and geology, the latter two of which use 'years before the present'. Although the absolute numerical values of astronomical and historical years only differ by one before year 1, this difference is critical when calculating astronomical events like eclipses or planetary conjunctions to determine when historical events which mention them occurred.

A zero year was first used by the eighteenth century French astronomers Philippe de La Hire (1702) and Jacques Cassini (1740). However, both of these astronomers used the applicable AD/BC designations of Latin and French with their year zero, thus near the epoch the years were designated 2 BC, 1 BC, 0, 1 AD, 2 AD, etc. They did not use −/0/+. During the nineteenth century, astronomers designated years with either BC/0/AD or −/0/+. Astronomers did not exclusively use the −/0/+ system until the mid twentieth century.

ee also

* ISO 8601


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Year zero — There is no year zero in the widely used Gregorian calendar, nor in its predecessor, the Julian calendar. Under those systems, the year 1 BC is followed by AD 1. However, there is a year zero in astronomical year numbering (where it coincides… …   Wikipedia

  • Year — A year (from Old English gēar) is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic. In astronomy, the… …   Wikipedia

  • Astronomical naming conventions — In ancient times, only the Sun and Moon, a few hundred stars and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are… …   Wikipedia

  • astronomical map — Introduction       any cartographic representation of the stars, galaxies, or surfaces of the planets and the Moon. Modern maps of this kind are based on a coordinate system analagous to geographic latitude and longitude. In most cases, modern… …   Universalium

  • Zero-based numbering — is numbering in which the initial element of a sequence is assigned the index 0, rather than the index 1 as is typical in everyday circumstances. Under zero based numbering, the initial element is sometimes termed the zeroth element, rather than… …   Wikipedia

  • Liturgical year — For Dom Guéranger s series of books, see The Liturgical Year. Christian year redirects here. For John Keble s series of poems, see The Christian Year. Part of a series on Christianity …   Wikipedia

  • Gregorian calendar — For the calendar of religious holidays and periods, see Liturgical year. For this year s Gregorian calendar, see Common year starting on Saturday. 2011 in other calendars Gregorian calendar 2011 MMXI …   Wikipedia

  • ISO 8601 — Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date and time related data. It was issued by the International Organization for… …   Wikipedia

  • Century — For other uses, see Century (disambiguation). Centuries , Centenary , Centennial , and Centennials redirect here. For other uses, see Centuries (disambiguation), Centenary (disambiguation), Centennial (disambiguation), and Centennials… …   Wikipedia

  • Mesoamerican Long Count calendar — Long Count redirects here. For the 1927 boxing match, see The Long Count Fight. Detail showing three columns of glyphs from a portion of the 2nd century CE La Mojarra Stela 1. The left column gives a Long Count date of 8.5.16.9.7, or 156 CE. The… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”