Astronomical year numbering
Astronomical year numbering is based on
The prefix AD and the suffixes CE, BC or BCE (Common Era, Before Christ or Before Common Era) are dropped.
The system is so named due to its use in
Usage of the year zero
In his
Cassini gave the following reasons for using a year 0:[10]
The year 0 is that in which one supposes that Jesus Christ was born, which several chronologists mark 1 before the birth of Jesus Christ and which we marked 0, so that the sum of the years before and after Jesus Christ gives the interval which is between these years, and where numbers divisible by 4 mark the leap years as so many before or after Jesus Christ.
— Jacques Cassini
Fred Espenak of NASA lists 50 phases of the Moon within year 0, showing that it is a full year, not an instant in time.[4] Jean Meeus gives the following explanation:[11]
There is a disagreement between astronomers and historians about how to count the years preceding year 1. In [Astronomical Algorithms], the 'B.C.' years are counted astronomically. Thus, the year before the year +1 is the year zero, and the year preceding the latter is the year −1. The year which historians call 585 B.C. is actually the year −584. The astronomical counting of the negative years is the only one suitable for arithmetical purpose. For example, in the historical practice of counting, the rule of divisibility by 4 revealing Julian leap-years no longer exists; these years are, indeed, 1, 5, 9, 13, ... B.C. In the astronomical sequence, however, these leap-years are called 0, −4, −8, −12, ..., and the rule of divisibility by 4 subsists.
— Jean Meeus, Astronomical Algorithms
Signed years without the year zero
Although he used the usual French terms "avant J.-C." (before Jesus Christ) and "après J.-C." (after Jesus Christ) to label years elsewhere in his book, the Byzantine historian Venance Grumel (1890–1967) used negative years (identified by a minus sign, −) to label BC years and unsigned positive years to label AD years in a table. He may have done so to save space and he put no year 0 between them.[12]
Version 1.0 of the
See also
- Julian day, another calendar commonly used by astronomers
- Astronomical chronology
- Holocene calendar
- ISO 8601
References
- ^ a b c d Espenak, Fred. "Year Dating Conventions". NASA Eclipse Web Site. NASA. Archived from the original on 8 February 2009. Retrieved 19 February 2009.
- ^ a b Jacques Cassini, Tables Astronomiques (1740), Explication et Usage pp. 5 (PA5), 7 (PA7), Tables pp. 10 (RA1-PA10), 22 (RA1-PA22), 63 (RA1-PA63), 77 (RA1-PA77), 91 (RA1-PA91), 105 (RA1-PA105), 119 (RA1-PA119). (in French)
- ^ Simon Newcomb, "Tables of the Motion of the Earth on its Axis and Around the Sun" in Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac, Volume VI: Tables of the Four Inner Planets, (United States Naval Observatory, 1898), pp. 27 & 34–35.
- ^ a b Fred Espenak, Phases of the Moon: −99 to 0 (100 to 1 BCE) Archived 5 June 2009 at the Wayback Machine NASA Eclipse web site
- ^ Johannes Kepler, Tabulae Rudolphinae (1627) Pars secunda, 42 (Zu Seite 191), 48 (197), 54 (203), 60 (209), 66 (215), 72 (221), 78 (227). (Latin)
- ^ Tabulae Astronomicae – Philippo de la Hire (1702), Tabulæ 15, 21, 39, 47, 55, 63, 71; Usus tabularum 4. (Latin)
- ^ Robert Kaplan, The nothing that is (Oxford: Oxford University Press, 2000) 103.
- ^ Dick Teresi, "Zero", The Atlantic, July 1997 (see under Calendars and the Cosmos).
- ^ L. E. Doggett, "Calendars" Archived 10 February 2012 at the Wayback Machine, Explanatory Supplement to the Astronomical Almanac, ed. P. Kenneth Seidelmann, (Sausalito, California: University Science Books, 1992/2005) 579.
- ^ Jacques Cassini, Tables astronomiques, 1740, Explication et Usage p. 5, translated by Wikipedia from the French:
"L'année 0 est celle dans laquelle on suppose qu'est né Jesus-Christ & que plusieurs Chronologistes marquent 1 avant la naissance de J. C. & que nous avons marquée 0, afin que la somme des années avant & après J. C. donne l'intervalle qui est entre ces années, & que les nombres divisibles par 4 marquent les années bissextiles tant avant qu'après Jesus-Christ." - ^ Jean Meeus, Astronomical Algorithms (Richmod, Virginia: Willmann-Bell, 1991) 60.
- ^ V. Grumel, La chronologie (Paris: Presses Universitaires de France, 1958) 30. (in French)
- ^ Biron, P.V. & Malhotra, A. (Eds.). (28 October 2004). XML Schema Part 2: Datatypes (2nd ed.). World Wide Web Consortium.