EasterDate

Easter Date

Algorithms

Calculates the easter date

function EasterDate(year: Integer): TDateTime;

function EasterDateJulian(year: Integer): TDateTime;

Description

Calculates the date of Easter sunday for any year between 1 and 2399 according to the famous easter formula developed by Carl Friedrich Gauss for the gregorian calendar. In fact the actual algorithm used is a variation of the original formula. For years outside the range from 1 to 2399 the exception E_OutOfAlgorithmRange is raised. For the years before the calendar reform of 1582 the algorithm for the Easter date is different and the EasterDateJulian function is used internally instead, and as the orthodox christians use the julian calendar for the calculations of the holidays till today the function EasterDateJulian is also available.

Easter is defined to be the first Sunday after the first full moon after the March equinox (starting of spring). However, the actual date follows the formula which can occasionaly deviate from the purely astronomical calculation, as the formula simplifies the equinox being always on March 21st, as well as the full moon calculation is simplified.

Reference

These functions are based upon chapter 8 of "Astronomical Algorithms".