How does Emacs calculate Easter Sunday?

How does Emacs calculate Easter Sunday?

[Enda]

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holiday-christian-holidays


In Lisp buffer C-j:

((holiday-easter-etc) (holiday-fixed 12 25 "Christmas") (if calendar-christian-all-holidays-flag (append (holiday-fixed 1 6 "Epiphany") (holiday-julian 12 25 "Eastern Orthodox Christmas") (holiday-greek-orthodox-easter) (holiday-fixed 8 15 "Assumption") (holiday-advent 0 "Advent"))))


Easter Sunday is there:

holiday-easter-etc


How does Emacs calculate it?, and how can I can put 'Easter Monday' in my calendar.


Best wishes,

Enda

P.S. Easter Monday is the day after Easter Sunday.

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Re: How does Emacs calculate Easter Sunday?

[Peter Dyballa]

Am 05.07.2012 um 21:02 schrieb Enda:

> holiday-easter-etc
> 
> 
> How does Emacs calculate it?, and how can I can put 'Easter Monday' in my calendar.

Write the text "holiday-easter-etc" into some buffer in GNU Emacs. It's also possible to copy it from somewhere, for example my Email, and yank into some buffer. Then position the text cursor somewhere in this function's name. Now you can type C-h f and press RET in mini-buffer. The *Help* which has opened contains a hyper-link to holidays.el. Follow it! Can you see the calculations? Can you also see how to possibly add Easter Monday to the list of (christian) holidays?

Besides this, Ed Rheingold, the original author of the GNU Emacs calendar functions, has written articles about this and other calendars. Maybe they're still available on the internet.

--
Greetings

  Pete

Increase the size of your bike by at least *five* inches!

RE: How does Emacs calculate Easter Sunday?

[Drew Adams]

>*Help*...contains a hyper-link to holidays.el. Follow it! 
> Can you see the calculations?

FWIW, I remember reading that code many years ago and being amazed by it - in
particular, the Easter algorithm/definition.  It involves both the moon and the
sun: first Sunday after the first full moon after the Spring equinox (in the
northern hemisphere).  Definitely an interesting read.  See also
http://en.wikipedia.org/wiki/Easter.

Re: How does Emacs calculate Easter Sunday?

[Peter Dyballa]

Am 05.07.2012 um 22:15 schrieb Drew Adams:

> It involves both the moon and the
> sun: first Sunday after the first full moon after the Spring equinox (in the
> northern hemisphere).

And Easter also stands for a clash of cultures, or genders: moon and female vs. sun and male. Or their marriage... At least for some part of the world. (Christians liked to recycle local traditions in order to make the adoption of the new religion easy in those early days. So Easter is probably much elder than a few thousand years. And folks then could calculate the date without GNU Emacs! Incredible.)

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Greetings

  Pete       (:
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