Tony Finch - Twitter echo chamber fail

dotatfanf wrote
on 3rd October 2010 at 20:14
Previous Entry Add to Memories Share Next Entry

Twitter echo chamber fail


(Leave a comment)
From:simont
Date:2010-10-04 15:30 (UTC)
(Link)
And yet, was presumably a complete coincidence.

The only way it could not be a coincidence would be if they considered lots of possible periods (in years) for the Gregorian calendar and picked the one which made the number of days come out to a multiple of 7. (Equivalently, I suppose, look for a good rational approximation to 1/7 of the number of days in a year, and use its denominator as the calendar period.)

I wonder if anyone DID propose any alternatives to the gregorian calendar: obviously you could do something other than the 100-400 exceptions, especially if you're willing to alter the 4-year cycle[1], but I don't know if any would have made equal sense, or had ever been suggested.

At Eastercon 2003 someone gave a talk suggesting a 33-year cycle containing 8 leap years, which he claimed gets an even better approximation to the true length of a year than 97/400. (It appears to be a continued-fraction convergent of the true length.) He also had a very silly conspiracy theory about how some people actually planned to implement that version in the 16th century in order to make the date of Easter work out more sensibly, but I can't remember any of the details.
(Reply) (Parent) (Thread)
From:fanf
Date:2010-10-04 15:38 (UTC)
(Link)
"More sensibly"?! The Gregorian rules for Easter are deliberately awkward to minimise the likelihood of coinciding with Passover. Anti-semitism isn't very sensible even in the 16th C...
(Reply) (Parent) (Thread)
From:simont
Date:2010-10-04 15:50 (UTC)
(Link)
Oh god, I'd forgotten Passover Sense Multiple Festival / Collision Detect. I don't recall the Eastercon 33-year guy saying how he intended to get round that one...
(Reply) (Parent) (Thread)
From:cartesiandaemon
Date:2010-10-05 10:23 (UTC)
(Link)
What happened? I learned a lot about the date of passover and easter, but not this.
(Reply) (Parent) (Thread)
From:fanf
Date:2010-10-05 14:42 (UTC)
(Link)
I think the details are described in "Calendrical Calculations", and I can't remember them because they are somewhat arcane.

But in essence, Pope Gregory did more than adjust the calendar to match the year more precisely. He also adjusted the rules for Easter, making them more complicated to satisfy various political goals. I can't remember now whether the adjustments also looked to the Eastern (Orthodox) church as well as the Jews- probably not since they continued to use the Julian calendar and the ecclesiastical equinox of 21st March, so their Easter would be unlikely to match the others. Dunno.
(Reply) (Parent) (Thread)
From:cartesiandaemon
Date:2010-10-05 15:13 (UTC)
(Link)
Thanks. I couldn't see why it would make any difference if Easter remains _normally_ just after passover, but it sounds like the sort of thing I'm not at all surprised happened.
(Reply) (Parent) (Thread)
From:cartesiandaemon
Date:2010-10-04 15:42 (UTC)
(Link)
The only way it could not be a coincidence would be if they considered lots of possible periods (in years) for the Gregorian calendar and picked the one which made the number of days come out to a multiple of 7.

Well, yes. It seemed unlikely that they WOULD have done, but also, they COULD have done. You could do the 33 year thing, or perhaps something similar but which decides only which normal 4-year leap years to skip. And making the days of the week repeat might be a mild advantage. (I can't see why it would be, but it would be tidy).

I was thinking of the 33-cycle thing. I saw it first invented by Mark Dominus (http://blog.plover.com/calendar/leapday.html) and I don't know if anyone suggested it before that or not. He said ancient persians (?) had something similar but more complicated.
(Reply) (Parent) (Thread)
From:cartesiandaemon
Date:2010-10-04 15:43 (UTC)
(Link)
I'm sure I heard some people discussing the 33 calendar on LJ. IIRC the advantages are that someone will hopefully remember the last 33-year anomoly, so there won't be any anomolies so rare people will not be ready for them. But the disadvantage is that you can't calculate leap years approximately by testing the year for division by 4, you need to do the division by 33.
(Reply) (Parent) (Thread)
From:nonameyet
Date:2010-10-05 07:05 (UTC)
(Link)
http://en.wikipedia.org/wiki/Iranian_calendar
(Reply) (Parent) (Thread)
From:nonameyet
Date:2010-10-05 21:15 (UTC)
(Link)
Sorry.
The Iranian calendar seems to have 8 leap days in 33 years: http://en.wikipedia.org/wiki/Iranian_calendar
(Reply) (Parent) (Thread)
From:pne
Date:2010-11-02 08:03 (UTC)
(Link)
This page is all about alternative leap year calculations (and his entire site has quite a lot of information on calendars and variations thereof, including his proposal for two perpetual calendars called "Symmetry 454" and "Symmetry 010").

He mentions the 8/33 rule but prefers a 52/293 one.

Apparently, which rule you choose depends on the length of the year you want to optimise for: time between successive equinoxes or between successive solstices, for example, will produce slight different lengths. (I'm afraid I don't remember details since I've only skimmed his pages - they're long and full of maths.)

Edited at 2010-11-02 08:04 (UTC)
(Reply) (Parent) (Thread)
From:fanf
Date:2010-11-02 09:34 (UTC)
(Link)
Interesting link, thanks! Re lengths of the year, the Gregorian calendar is intended to match the period between vernal equinoxes, because of the importance of Easter.
(Reply) (Parent) (Thread)

(Leave a comment)

Powered by LiveJournal.com