The full moon used to calculate the date of Easter. This full moon does not correspond to any astronomical event, but is a historical artifact determined from tables. An algorithm due to J. H. Conway which is valid for years Y between 1900 and 2200 calculates the Paschal full moon as
where
denotes a congruence , i.e., the remainder when n is divided by m, and
is the golden number, except that when this gives April 19, it is changed to April 18, and when it gives April 18 and
, then it is changed to April 17. The following table gives the dates of the Paschal full moons for 1980-2009.
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A modification of (1) to
where
is the floor function and
extends the range of valid years from
to 
in the Gregorian calendar.
For the Julian calendar, the correct equation is
(1)
where
denotes a congruence , i.e., the remainder when n is divided by m, and(2)
is the golden number, except that when this gives April 19, it is changed to April 18, and when it gives April 18 and
, then it is changed to April 17. The following table gives the dates of the Paschal full moons for 1980-2009.[Ctrl+A 全部选择 提示：你可先修改部分代码，再按运行]
A modification of (1) to
(3)
where
is the floor function and(4)
extends the range of valid years from
to in the Gregorian calendar. For the Julian calendar, the correct equation is
(5)
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