Mega Code Archive
Good Thursday and Easter DAte function
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Title: Good Thursday and Easter DAte function
Question: Here is another function that calculates the Good Thursday and any other related date for eny year.
I know that there is another article with the same subject but it is not exactly correct since it requires a correction factor.
The algorithm provided here is straightforward in the sense that it calculates the Good Thursday (which is the jewish passover) as the thursday ocurring in the same week as the first spring full moon.
Obviously the function can be easily adapted to calculate any full moon down to the second.
Answer:
function good_thursday(year : integer):tdatetime;
const full_moon :tdatetime = 34804.33889; {15/4/95 8:08}
sunday : tdatetime = 1;
sinodic_month : tdatetime = 29.53058912;
var equinoccio : tdatetime;
lunar_months : double;
full_moon,weeks : double;
begin
if year if year year:=year+2000
else
year:=year+1900;
equinoccio:=encodedate(year,3,21);
lunar_months := 10000 - Int(10000 - (equinoccio - full_moon) / sinodic_month);
full_moon := full_moon + sinodic_month * lunar_months;
weeks := 10000 - Int(10000 - (full_moon - sunday) / 7);
good_thursday := sunday + 7 * weeks - 3;
end;
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