Easter Sunday

Have you noticed that Easter Sunday falls on a different week each year?

How do they calculate the date?

Easter Sunday is determined as; wait for it…

The first Sunday after the full moon which happens on or after the equinox in March.

If the full moon occurs on a Sunday, Easter Sunday is the Sunday after.

Easter Sunday can fall on or between March 22 and April 25.

The history of this significant date is long and interesting. Look it up sometime! The congregation used to be told the date of Easter as soon as the Clergy had calculated it; normally only a few weeks beforehand.

This wasn’t really practical, in the modern age, so some boffin worked it out mathematically.

The algorithm is as follows:

#Set up some variables
Let G = (Y mod 19) + 1
Let C = (Y div 100) + 1
Let X = (3C div 4) – 12
Let Z = ((8C + 5) div 25) – 5
Let D = (5Y div 4) – X – 10
Let E = (11G + 20 + Z – X) mod 30

#If E is 25 and G is greater than 11 Or E is equal to 24 then 
#add 1 to E and let N = 44 - E
If E = 25 AND G > 11, OR E = 24, then
    add 1 to E Let N = 44 – E

# If N is less than 21 add 30 to N
If N < 21,
    add 30 to N

#Calculate P
Let P = N + 7 – ((D +N) mod 7)

#If P is less than or equal to 31 then its on Pth March else calculate it.
If P <= 31 then
    Easter Sunday is on P March
Else
    Easter Sunday is on (P – 31) April

Write a program to calculate the Easter date for this year (which you can easily check) then find out the date of Easter for a few other years.