Well Shrove Tuesday is here ( pancake day ) which means Lent is tomorrow and Easter soon after.
How do we know ? well ...
Well calculate the epact for this year (using Golden Number and mod(19) if you want to cheat a bit) to give you the date of the Paschal New Moon, which is the ecclesiastical new moon after the vernal equinox. (20-21 march )
Add 13 days.
Go to the next Sunday and that is Easter Sunday.
Count back 41 days not including Sundays.
That's Pancake Day :)
Or for you non ecclesiastical geeks put this in excel and make the cell format a date.
=DOLLAR(("4/"&A1)/7+MOD(A1,19)-7,30)14%,)7-6 and put the year in A1 and count back 41 as above.
Epact days ? Well they are the cumulative days left over after 12 ecclesiastical months. This is a set of 12 months of alternating 29 and 30 day months that doesn't quite make 365 so there are some left over.
Leap years ? Well we need a discussion about the new fan dangled Gregorian calendar 19 year cycles and the "Golden Number"
But for now I need eggs, milk , flour ...