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Encyclopedia > Astronomical year numbering

Astronomical year numbering is based on BCE/CE (or BC/AD) 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 BCE/CE or BC/AD are dropped. So the year 1 BCE is numbered 0, the year 2 BCE is numbered −1, and in general the year n BCE is numbered (1−n). The numbers of CE years are not changed, but CE (or AD) is not used, being replaced by either no sign or a positive sign. 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 Common Era (CE), also known as the Christian Era and sometimes the Current Era, is the period of measured time beginning with the year 1 until the present. ... Anno Domini (In the Year of the Lord), abbreviated as AD or A.D. defines an epoch based on the traditionally-reckoned year of the birth (or actually Incarnation) of Jesus of Nazareth. ... The decimal (base ten or occasionally denary) numeral system has ten as its base. ... The integers consist of the positive natural numbers (1, 2, 3, …), their negatives (−1, −2, −3, ...) and the number zero. ... A year zero does not exist in the Christian Era and thus also does not currently exist in the calculation of times in most cultures. ... 0 (zero), alternatively called naught, nil, nada, ought, zilch, zip, nothing or nought, is both a number and a numeral. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ...


The system is so named due to its use in astronomy. Few other sciences 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. Lunar astronomy: the large crater is Daedalus, photographed by the crew of Apollo 11 as they circled the Moon in 1969. ... Wikimedia Commons has media related to: History For other senses of this word, see history (disambiguation). ... Pinus taeda Cross section showing annual rings, Cheraw, South Carolina Pine stump showing growth rings Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree ring patterns. ... Archaeology, archeology, or archæology (from the Greek words αρχαίος = ancient and λόγος = word/speech/discourse) is the study of human cultures through the recovery, documentation and analysis of material remains and environmental data, including architecture, artifacts, biofacts, human remains, and landscapes. ... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ...


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 BC/AD designations of Latin and French with their year zero, thus near the epoch the years were designated 2 BC, 1 BC, 0, AD 1, AD 2, 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. (17th century - 18th century - 19th century - more centuries) As a means of recording the passage of time, the 18th century refers to the century that lasted from 1701 through 1800. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Philippe de la Hire (or Lahire or Phillipe de La Hire), French mathematician and astronomer, was born in Paris on March 18, 1640, and died there on April 21, 1719. ... Jacques Cassini (February 8, 1677 - April 18, 1756) was a French astronomer, son of Giovanni Domenico Cassini Cassini was born at the Paris Observatory. ... Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s The 20th century lasted from 1901 to 2000 in the Gregorian calendar (often from (1900 to 1999 in common usage). ...


See also


  Results from FactBites:
 
CalendarHome.com - Astronomical year numbering - Calendar Encyclopedia (341 words)
So the year 1 BCE is numbered 0, the year 2 BCE is numbered −1, and in general the year n BCE is numbered (1−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.
However, both of these astronomers used the applicable BC/AD designations of Latin and French with their year zero, thus near the epoch the years were designated 2 BC, 1 BC, 0, AD 1, AD 2, etc. They did not use −/0/+.
Year numbering - Wikipedia, the free encyclopedia (1304 words)
Year numbering is the assignment of integers to calendar years for the purpose of uniquely identifying the years.
The numbering system devised by Dionysius Exiguus in AD 525 is still the most common, which is based on the year he assigned to the birth of Jesus, It is now believed that he was born four to eight years earlier.
In AH 17, the year AH 1 was assigned to the year during which Muhammad emigrated from Mecca to the city of Medina.
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