Oops! You goofed. In your first book, “The Straight Dope,” you say that “Easter falls on the first Sunday subsequent to the first full moon after the vernal equinox.” This isn’t necessarily true. The date of Easter is determined by an ecclesiastical formula (see “Astronomical Algorithms” by Jean Meeus,
Divide by Quotient Remainder
the year x 19 - a
the year x 100 b c
b 4 d e
b 8 25 f -
b-f 1 3 g -
19a b-d-g 15 30 - h
c 4 i k
32 2e 2i-h-k 7 - l
a 11h 22l 451 m -
h l-7m 114 31 n p
Then n = number of month (3=March, 4=April), and p 1 = day of the month on which Easter falls.
The actual (ecclesiastical) date of Easter does not always fall on the astronomical date of Easter. For example, in 1981 the vernal equinox fell on March 20, the next full Moon was on April 19, and the following Sunday was
April 26. However, Easter Sunday in 1981 actually fell on April 19, as computed by the above formula.
The next time that the astronomical date of Easter will differ from its actual ecclesiastical date will be in 2019, when the astronomical date is March 24, but the ecclesiastical formula gives the actual date of April 21.
[Note: This message has been edited by Ed Zotti]