Numerous implementations of this algorithm in various other languages (including C#), as well as historical details, etc., can easily be found via web search if you're interested.
By the way, Mr. Duffett-Smith's book (and I presume his later books on computer astronomy) is an absolute gem. If you've ever read predictions of eclipses, etc. and wondered "how did they calculate that?" his books will make all such mysteries plain.
(Presented “as-is” and without warranty or implied fitness; use at your own risk.)
// Computes the date of Easter for a
// given year beginning from 1583.
// Method is that described in "Butcher's
// Ecclesiastical Calendar" (1876),
// and as given in:
// "Practical Astronomy With Your Calculator"
// by Peter Duffett-Smith (Cambridge, 1981).
let easter year =
// Return integer and fractional
// part of a division as a tuple.
let (/%) l r = (l/r),(l%r)
// The calculation.
let a = year%19
let (b,c) = year/%100
let (d,e) = b/%4
let f = (b+8)/25
let g = (b-f+1)/3
let h = (19*a+b-d-g+15)%30
let (i,k) = c/%4
let l = (32+2*e+2*i-h-k)%7
let m = (a+11*h+22*l)/451
let (n,p) = (h+l+7*m+114)/%31
let e2009 = easter 2009
let e2010 = easter 2010
let e2011 = easter 2011
"Easter this year is: %s"
System.Console.ReadLine() |> ignore