Talk:Computus

Definitions

There are exactly TWO definitions of the date of Gregorian Easter Sunday. The Gregorian one is (for 1583 to 4999) in Clavius' Six Canons, and for perpetuity Clavius' Opera Mathematica Tomus V, both given authority by Gregory XIII's Bull Inter Gravissimas. The other one is the British Calendar Act of 1751 as enacted, of which the relevant parts are by law printed in the Church of England Book of Common Prayer. Both are arithmetic definitions, giving the Sunday AFTER a computed full moon date ON OR AFTER March 21st (they are very different in form, but agree completely in result).

The word "definition", or similar, should not be used to refer to arguments involving the 14th day of the moon, the Vernal Equinox, etc., etc. - those are merely considerations which led to the choice of the Papal definition (the British definition was chosen to give the same answers, but in an operationally-simpler manner and in English). Ideally, the Pope and the Archbishop (or the ISO 8601 people) would issue a superseding agreed executable form (such as JavaScript, which most computers can execute).

To facilitate this distinction, the Article and the Discussion need to be divided into three parts (by major headings, or on separate pages), to be read in turn : (1) arguments leading to the definitions, (2) the definitions themselves, (3) the consequences of the definitions. Each of those could have two parts, for Julian and Gregorian (and something about Easter on the Greek secular calendar with its different leap years).

There are other interesting consequences, apart from the histograms; the number of weeks between adjacent Easters, the minimum and maximum number of years between Easters of the same date, the spans of years containing all 35 possible dates, ... .

94.30.84.71 (talk) 21:25, 26 April 2011 (UTC)

This is a tempest in a teapot. Because both the rule in Inter gravissimas and the rule in the Calendar Act of 1750 specify the same dates for Easter, I do not support any further discussion beyond that already in the article at British Calendar Act and Book of Common Prayer. See my extensive discussion with 82.163.24.100 in the archive. — Joe Kress (talk) 23:59, 26 April 2011 (UTC)

P.S. That link should be to Calendar_%28New_Style%29_Act_1750 rather than to a redirector : Calendar (New_Style) Act 1750. Giving a false form is misleading. 94.30.84.71 (talk) 10:04, 27 April 2011 (UTC)

You have missed the main point entirely.

And the Calendar Act was not OF 1750, since the normal interpretation of that is that the Act was enacted in AD 1750. It was enacted in AD 1751 (OS/NS/Julian/Gregorian).

The TITLE of the Act is "Calendar (New Style) Act 1750", in which 1750 is the Regnal Year, and 1750 should only be used as part of the Title. Don't get confused by the Act having been passed in the (Annual) Parliament which started in January 1750, since that was an OS date with the year number changing in March. 94.30.84.71 (talk) 09:59, 27 April 2011 (UTC)

The original title of the Act was An act for regulating the commencement of the year; and for correcting the calendar now in use. The short title assigned in 1896 to the modern version is Calendar (New Style) Act 1750. A committee chose that title. Large sections of the original act have been removed so the modern version is "gutted". — Joe Kress (talk) 17:19, 28 April 2011 (UTC)

Therefore, one must be clear, both here and on the page about the Act, as to which parts refer to the original Act (I use "as enacted") and which to the modern version; and also as to which authorities are used for those wordings.

The best representation on the Web for the Act as enacted seems to be in Statutes at Large 1765 at Google Books.

In the version of the current Act presented on the Web by HMG at http://www.legislation.gov.uk/apgb/Geo2/24/23, the discursive Section 3 (in HTML) dealing with Easter is virtually the same as in 1765 ; and the text in the Easter Tables part (images), after the foot of Section 6, is corrupt.

The current Church of England Book of Common Prayer contains words and tables which would satisfy King George II's legislators if they were still alive. 94.30.84.71 (talk) 12:13, 8 May 2011 (UTC)

"As enacted" is not precise enough because all later amendments were also enacted. It might be best to refer to the original version "as enacted 1750/51" to indicate both the 25 March and 1 January beginnings of the year. — Joe Kress (talk) 03:55, 9 May 2011 (UTC)

Another printing of the original act with all tables and the first amendment is in Archibald John Stephens, The statutes relating to the ecclesiastical and eleemosynary institutions of England, Wales, Ireland, India, and the colonies, Volume 1 (1845) 828–847. — Joe Kress (talk) 21:05, 13 May 2011 (UTC)

Miscellaneous

Why is it not something more simple such as the 2nd sunday in April -N7I2S5 (talk) 20:48, 1 July 2011 (UTC)

The UK "Easter Act 1928" permitted, if agreeed world-wide, a similar rule. But, now that we have ISO 8601 week dates, it would be better to fix exactly one date, the same each year, yyyy-W15-7. 94.30.84.71 (talk) 11:30, 17 November 2011 (UTC)

Merge with Easter Controversy article?

I think that this article's history section should be fairly brief. Merger would expand it to unwieldy lengths. I vote for keeping the Easter Controversy article separate, and removing the tag proposing the merger.--Mockingbird0 (talk) 04:29, 8 July 2011 (UTC)

The 19-year Cycle is Metonic

The 19-year cycle is the Metonic cycle or Enneadecaeteris; discussions of Easter commonly use "Metonic". That link should be added somewhere within the text of the article, perhapa as "the 19-year Metonic cycle". One respected, but not expert, site, refers instead to the longer Callipic cycle. 94.30.84.71 (talk) 11:53, 17 November 2011 (UTC)

Modulo operation when dividend is negative

There are different definitions for the modulo operation which give different results when one of the operands is negative, and different programming languages implement it differently. For example, if year was -1 (i.e. 2 BC. I know Easter didn't exist back then, but algorithms should have a consistent definition regardless), then "Y mod 19" would return -1 in C and Java, while it would return 18 in Python and Ruby. So my questions are:

1. Do the different modulo operations produce different results?
2. If so, which one would give the theoretically correct date ("theoretical", if the year is before Easter existed)?
3. If so, should the correct one be specified in the article?

-- 208.80.119.68 (talk) 02:52, 16 December 2011 (UTC)