A little calculator to get the date of Easter in various years using an algorithm from the Astronomy FAQ. MNO
#!/bin/sh
# next line restarts with tclsh \
exec tclsh $0 ${1+"$@"}
#
# Author: Mark Oakden http://wiki.tcl.tk/MNO
# Version: 1.0
#
# calculate Easter Sunday using the algorithm given at
# http://www.faqs.org/faqs/astronomy/faq/part3
#
# assumes Gregorian calendar
#
proc easterdate { year } {
#
# G is "golden number"
#
set G [expr {($year % 19) + 1}]
#
# H is intermediate in calculating C
#
set H [expr {int($year / 100)}]
#
# C is "century term"
#
set C [expr {(-1 * $H) + int($H/4) + int(8*($H+11)/25)}]
#
# first we need the paschal full moon.
# the following is in days before april 19 with a couple of exceptions
#
set rawdays [expr {((11*$G)+$C) % 30}]
#
# exceptions if rawdays = 0 use days=1
# if rawdays = 1 and G >= 12 use days=2
# else use days=rawdays
#
if { $rawdays == 0 } then {
set days 1
} elseif { $rawdays == 1 && $G >= 12} {
set days 2
} else {
set days $rawdays
}
#
# now find the day that this falls on:-
#
set apr19 [clock scan "19 April $year 12:00"]
# %w is week day number Sun=0
set pfmweekdaynum [clock format [expr {$apr19 - ($days*24*60*60)}] \
-format "%w"]
#
# Easter sunday is the next Sunday _strictly_ after PFM, so
# if pfmweekday is sunday, we want 7 days after pfm
# if pfmweekday is monday, we want 6 days after pfm etc.
# i.e. we want to take (7-pfmweekdaynum) days after pfm
#
set easterdate [expr {$apr19 - (($days - 7 + $pfmweekdaynum)*24*60*60)}]
return $easterdate
}
for { set i 1995 } { $i <= 2015 } { incr i } {
puts "Easter Sunday in $i will be on [clock format [easterdate $i] -format {%b %d}]"
}PT writes: In a strange twist of fate - the very day this was posted a collegue wished to know this date for 2004. Tcl wins the day!
TFW OK, now someone with more time on their hands than me compute the Orthodox dates. Look at http://www.assa.org.au/edm.html#OrthCalculator for a clue.
GWLESTER Put braces arround expressions just like they should be.