Ed Davies quoted:
>> 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 is from section 4.3.2.1 of the final draft of ISO8601:2000.
This does not express a complete algorithm, of course, since it is
not tied to the days of the week. One presume the zero point of 1875
was selected as a practical compromise with historical realities.
One questions whether the Gregorian calendar can be used to express
dates before 1582-10-15, and it is ambiguous for large parts of the
world until the mid-eighteenth century. Still in 1875, it had not
reached all locales. Etc.
Zefram wrote:
> Pope Gregory, of course, used a different epoch. The original
> Papal Bull
> didn't use a well-known event such as this, but instead effectively
> said
> 1582 October 5 Julian = 1582 October 15 Gregorian.
This is very familiar territory since I had two semesters of the
History of Astronomy from an Augustinian priest. I had not
previously read through the Papal Bull in question, however. I
wouldn't rely on this as a fundamental reference, but see the
translation at:
http://personal.ecu.edu/mccartyr/intGrvEng.html
A few comments. First, the name of the Bull is "Inter Gravissimas"
or roughly "Among the most serious". These are not issues to be
trifled with. Second, from paragraph 5:
"Our dear son Antonio Lilio, professor of science and medicine,
brought to us a book, written at one time by his brother Aloysius
[Luigi],
in which this one showed that, by means of a new cycle of epacts
which he had devised, and who directed his own particular Golden
Number pattern and accomodated the entirety of any solar year,
every [defect of] the calendar collapsed, and the constant calculations
would endure for every generation. He was, thus, able to restore and
explain how the calendar itself will never need published any further
change."
A worthy goal. That residual discrepancies (that were presumably
within the measurement error in the sixteenth century) will
ultimately require currently unscheduled modifications to the
Gregorian calendar, does not diminish the achievement of Aloysius/Luigi.
A successful proposal to reform civil time (as with the civil
calendar) should exhibit this same worthy goal of actually improving
the status quo, rather than simply arranging to ignore a reality that
will return with a vengeance after 600 years.
Gregory also had a refreshing attitude toward the standards process:
1) "This new project of the restoration of the calendar, summarized
in a small book, we forwarded a few years ago to the Christian princes
and to the large universities so that this work, which is the business
of all, is carried out with the consultation of all."
2) "Those having expressed their agreement to us, as we had sincerely
hoped, we have, with this consensus, arranged a gathering in the
Holy City, to reform the calendar, of the very qualified men on the
matter whom we had chosen from the principal countries of the
Christian world a long time before."
3) "Those, after having devoted much time and attention to this night
work and having discussed between them cycles which they had
collected from everywhere, old ones as well as modern ones, and
as they had carefully studied the reflections and the opinions of
erudite men who wrote on this subject, chose and prefered this
cycle of epacts,"
4) "adding to it elements which, after thorough examination, appeared
essential to the realization of a perfect calendar."
So, they: invested sufficient time to understand the issues -
recognized the extremely broad range of stake holders - sought their
advice and consent in characterizing the problem - invited
representatives to help craft the solution - and more to the point,
were looking for an actual solution, not some imaginary bandaid.
Rob Seaman
NOAO
Received on Tue Jun 06 2006 - 20:24:15 PDT