From: Hans Aberg (haberg@math.su.se)
Date: Thu Dec 20 2007 - 08:37:16 CST
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:
http://en.wikipedia.org/wiki/Star_date
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
http://en.wikipedia.org/wiki/Gregorian_calender
http://en.wikipedia.org/wiki/Julian_day
http://en.wikipedia.org/wiki/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
http://en.wikipedia.org/wiki/CE_mark
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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