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 -$H + int($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 } {
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!