On 08-Oct-06 Ted Harding wrote:
On 08-Oct-06 Tim Green wrote:
On 10/8/06, Ted Harding Ted.Harding@nessie.mcc.ac.uk wrote:
Specifically: The "calendar"/"clock" application in the Gnome panel is incorrect for the year 1752 (and therefore for all preceding years).
How did you get to 1752 without 254 clicks?
I didn't. Just clicked 254 times!
How wrong is it? For example, is it correct from Thursday 14th September through to Sunday 31st December?
Tim.
I suppose so (haven't checked in that much detail). But (as Adam also implies) 3-13 September are there when they shouldn't be, so previous dates have been pushed back 11 days in the weekly cycle. (That's seriously wrong!)
See also forthcomng reply to Adam.
Ted.
And it gets worse ... (the trouble with starting a hare is that one's tempted to continue chasing it).
In the Julian Calendar, there was a leap year every 4 years regardless (which was the cause of all the trouble, since the calendar year then "runs slow" relative to the annual revolution round the Sun, to the tune of 1 day every 128 years)[1].
The Gregorian Calendar omits the Leap Year in century years not exactly divisible by 400 (so only in 2000, 1600, 1200, ... is the last day of Feb Feb 29).
So I opened up the calendar in Gnome Clock again and clicked back to 1600 -- not a LY; then 1200 -- not a LY, but it should have been; and so on.
Upshot: Gnome Clock seems to use the Gregorian Algorithm for all time. So, even if you use it for pre-1752 dates and adjust by 11 days for the error in Sept 1752, you will get progressively out because it omits LYs where it shouldn't.
(Mind you, "cal 1066" is a damn sight easier than 1,960 mouse clicks).
[1] Not exactly true, since there was some sort of "clerical error" in the early years. The Julian Calendar was decreed by Julius Caesar in 45BC. Initially there were leap years every 3 years, until 9BC (12 in all, not counting 45BC); the next was 8AD, after which it was every 4 years.
The current value of the length of a year is 365.24219 days, hence a Leap Year every 4 years regardless will introduce an error of 4*(0.25 - 0.24219) = 0.03124 days every 4 years, which over 1/0.03124 = 32.0102 4-year cycles builds up to a whole day. Hence 1 day out per 128 years.
The change to the Gregorian Calendar was in fact decreed by Pope Gregory in 1582 (the Church having settled on a Julian system in 325AD [Council of Trent]), by which time the calendar was (1582 - 325)/128 = 9.8 (or 10) days out.
But his writ did not run to England by this time, since Henry VIII had already seen to that. So not until 1752 did Britain decided that there was a need to get into line with other countries (a precursor of current attitudes to the EU?), by which time we were (1752 - 325)/128 = 11.15 (or 11) days out.
Hence
$ cal 9 1752 September 1752 Su Mo Tu We Th Fr Sa 1 2 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Cheers, Ted.
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