RE: CLDR Usage of Gregorian Calendar Era Terms: BC and AD -- Can we please have "CE" and "BCE" ?

From: Hohberger, Clive (
Date: Thu Dec 20 2007 - 11:09:48 CST

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    The Julian day number ( ) has been in use on many computer systems for decades as a base for computation of other calendar systems.

    Now at 16:10, Thursday December 20, 2007 (UTC) the JDN is 2454455. The remainder of this value divided by 7 is 3, an integer expression for the day of the week with 0 representing Monday.

    The Julian date (JD) is a continuous count of days and fractions elapsed since the same initial epoch. The initial epoch defined as noon Universal Time (UT) Monday, January 1, 4713 BC in the proleptic Julian calendar. That noon-to-noon day is counted as Julian day 0.

    Currently the JD is 2454455.17361 as of the time of this writing.

    -----Original Message-----
    From: [] On Behalf Of Hans Aberg
    Sent: Thursday, December 20, 2007 8:37 AM
    To: James Kass
    Cc: Unicode Discussion
    Subject: Re: CLDR Usage of Gregorian Calendar Era Terms: BC and AD -- Can we please have "CE" and "BCE" ?

    On 20 Dec 2007, at 13:17, James Kass wrote:

    >> The simplest way to avoid the issue altogether is to use astronomical
    >> year numbering:
    > A good idea, but the phrase "astronomical year numbering"
    > may be too cumbersome for many. We'd want something simpler and more
    > catchy. How about "star date"?

    It got its name from its use in astronomy, not from stars, and "star date" is already in use:
    and not very well defined :-).

    But one might call it "astronomical calendar" or "common calendar", which is not any harder than "Gregorian calendar", agreeing that in the Julian Day (JDN) counting starting day 0 at January 1, -4712, every year divisible by 4 is a leap year, until October 4, 1582, which is followed by October 15, 1582, where-after years divisible by 100 but not 400 are excluded from being leap years. This produces a well defined calendar.

    The thing is that the Gregorian calendar was only introduced gradually by different countries, and is still not used for example by the Russian Orthodox church
    So tying the suggestions to the Gregorian calendar may not have the intended effect :-). It is also rare to see "AD" or "A.D." on modern dates, and "CE" means something else in the Europe

    So formally, one tends to use the astronomical calendar when dealing with modern dates, but switching to another calendar, the Julian or Gregorian calendar, when dealing with older dates. There, one might think the appropriate method would be to either quote the dates as written (as the historical records might be unclear of calendar syncing), or translate them into the modern astronomical calendar as a benefit to modern readers. It takes a long time bringing forth the full acceptance of the symbol 0 and negative numbers - those Medieval habits are strongly ingrained :-).

    As for calendar computations, it is simplest to provide computations back and forth to Julian Day Numbering (if possible, in view of that historical records might be unclear). Users can then use whatever calendar they prefer - it is just a matter of display in a modern computer, if dates are stored internally as JDNs.

       Hans Åberg
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