Quoted from "Practical Astronomy With Your Calculator" 3rd Edition, by
Peter Duffett Smith
1988, Cambridge University Press.
The date of Easter
Easter day, the date to which such moveable feasts as Whitsun and Trinity
Sunday are fixed, is
usually the first Sunday after the fourteenth day after the first new Moon
after March 21st. (For a
more precise definition see The Explanatory Supplement to the Astronomical
Ephemeris and
American Ephemeris and Nautical Almanac.) You can find the date of Easter
Sunday by the
method and tables given, for example, in the Book of Common Prayer, 1662,
or by one of
several methods devised by various mathematicians over the centuries. Here
I shall describe a
method devised in 1876 which first appeared in Butcher's Ecclesiastical
Calendar, and which is
valid for all years in the Gregorian calendar, that is from 1583 and
onwards. It makes repeated
use of the result of dividing one number by another number, the integer
part being treated
separately from the remainder. A calculator displays the result of such a
division as a string of
numbers before and after a decimal point. The numbers appearing before the
decimal point
constitute the integer part; the numbers after the decimal point constitute
the fractional part. The
remainder may be found from the latter by multiplying it by the divisor
(i.e. the number you have
just divided by) and rounding the result to the nearest integer value. For
example, 2000/19 =
105.263 157 9. The integer part is 105 and the fractional part is 0.263 157
9. Multiplying this by
19 gives 5.000000 100 so that the remainder is 5. I shall illustrate the
method by calculating the
date of Easter Sunday in the year 2000.
Method
Integer part
Remainder
1. Divide the year by 19
a
example: 2000/19=105.2631579
a=5
2. Divide the year by 100 b
c
example: 2000/100=20.000000
b=20 c=0
3. Divide b by 4 d
e
d=5 e=0
4. Divide (b+8) by 25 f
f=1
5. Divide (b-f+1) by 3 g
g=6
6. Divide (19a+b-d-g+15) by 30 h
h=29
7. Divide c by 4 i
k
i=0 k=0
8. Divide (32+2e+2i-h-k) by 7 L
l=3
9. Divide (a+11h+22L) by 451 m
m=0
10. Divide (h+L-7m+114) by 31 n p
n=4 p=22
11. Day of the month on which Easter Sunday
falls is p+1
p+1=23
Month number is n (=3 for March and =4
for April).
Easter Sunday 2000 is 23rd April
At 08:09 PM 6/10/99 +0100, Frank Evans wrote:
>I believe that for calculation by simple souls Easter is just the first
>Sunday after the first full moon after the equinox of 21 March. But I
>would like to find Easter several years ahead and do not know where to
>find lunar phases except for the current year. Or is there a handy
>table somewhere. There is one in the Oxford Companion to English
>Literature, extending over hundreds of years but it ends at the year
>2000. Can anyone help, please?
>--
>Frank Evans
