
One of Paul's documentation changes that I left out of the update was... +The year before the year 1 is the year 0, the year before that is +the year \-1, and so forth. If I recall correctly, there's no year zero: the sequence (going backward) is... 3 AD, 2 AD, 1 AD, 1 BC, 2 BC, 3 BC... ...or, for "Common Era" fans... 3 CE, 2 CE, 1 CE, 1 BCE, 2 BCE, 3 BCE.. Have our standard-making friends said anything on the matter? --ado

"Olson, Arthur David (NIH/NCI)" wrote on 2004-08-11 16:18 UTC:
One of Paul's documentation changes that I left out of the update was... +The year before the year 1 is the year 0, the year before that is +the year \-1, and so forth. If I recall correctly, there's no year zero: the sequence (going backward) is... 3 AD, 2 AD, 1 AD, 1 BC, 2 BC, 3 BC... ...or, for "Common Era" fans... 3 CE, 2 CE, 1 CE, 1 BCE, 2 BCE, 3 BCE..
Have our standard-making friends said anything on the matter?
Historical practice was that way simply because the "anno domini" technology has allegedly been developped by some monk of the name Dionysius Exiguus in the 6th century and was finally rolled-out by the church around the year 1000 A.D. But the technology of negative numbers and the number zero became only widely known after decimal numbers became widely accepted and popular, which was certainly not before Fibonacci's textbook "Liber Abacci", was first published in 1202. The idea of the year zero has been widely used in modern astronomical tables. It was more recently also sanctioned by ISO 8601:2000 for the international date notation, which uses the prolaptic Gregorian calendar with year zero: --------------------------------------------------------------------- 4.3.2 Date and time reference systems 4.3.2.1 The Gregorian calendar This International Standard uses the Gregorian calendar for the identification of calendar days. The Gregorian calendar provides a reference system consisting of a, potentially infinite, series of contiguous calendar years. Consecutive calendar years are identified by sequentially assigned year numbers. A reference point is used which assigns the year number 1875 to the calendar year in which the "Convention du mètre" was signed at Paris. The Gregorian calendar distinguishes common years with a duration of 365 calendar days and leap years with a duration of 366 calendar days. A leap year is a year whose year number is divisible by four an integral number of times. However, centennial years are not leap years unless they are divisible by four hundred an integral number of times. This International Standard allows the identification of calendar years by their year number for years both before and after the introduction of the Gregorian calendar. For the determination of calendar years and year numbers only the rules mentioned above are used. For the purposes of this International Standard these rules are referred to as the Gregorian calendar. The use of this calendar for dates preceding the introduction of the Gregorian calendar (i.e. before 1582) should only be done by agreement of the partners in information interchange. NOTE 1 In the prolaptic Gregorian calendar the calendar year [0000] is a leap year. NOTE 2 No dates shall be inserted or deleted when determining dates in the prolaptic Gregorian calendar (this may be necessary for the calculation of dates in the Julian calendar before 1582). Also note that the year numbers of years before the calendar year [0001] differ from the year numbers in the BC/AD calendar system, where the year 1 BC is followed by the year 1 AD. [...] 4.7 Expansion By mutual agreement of the partners in information interchange it is permitted to expand the component identifying the calendar year, which is otherwise limited to at most four digits. This enables reference to dates and times in calendar years outside the range supported by complete representations, i.e. before the start of the year [0000] or after the end of the year [9999]. When expanded representations are used, provisions should be made to prevent confusion of the expanded representations, with other date and time representations used by the application. --------------------------------------------------------------------- ISO 8601 then also defines an extended year format, in which the year can be longer than four digits and outside the range 0000 to 9999, but it must then start with either + or -, e.g. today is +002004-08-11 Markus -- Markus Kuhn, Computer Lab, Univ of Cambridge, GB http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__

"Olson, Arthur David (NIH/NCI)" wrote on 2004-08-11 16:18 UTC:
Have our standard-making friends said anything on the matter?
For ctime and asctime, the C standard clearly specifies that the years before 1 are printed as 0, -1, -2,.... It's said that for many years. Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk> writes:
Historical practice was that way simply because the "anno domini" technology has allegedly been developped by some monk of the name Dionysius Exiguus in the 6th century and was finally rolled-out by the church around the year 1000 A.D.
As I understand it we shouldn't blame this on Dionysus Exiguus, as his system didn't address the issue of numbering years before 1. The blame more properly falls on the Venerable Bede, who didn't know about zero when he extended the system to cover the years before 1 in his classic work the Ecclesiastical History of the English People, completed in 731. The modern computer tradition (e.g., the one used by the ISO, and by Dershowitz and Reingold's wonderful book "Calendrical Calculations") is firmly on the side of having a year 0. This follows in a long tradition: Cassini, Goethe, Hugo, and others all championed the year zero.
participants (3)
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Markus Kuhn
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Olson, Arthur David (NIH/NCI)
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Paul Eggert