Calculating Julian Easter date

Question

Hello,
I need to calculate the day of the of the Julian Easter
The Algorithm is e.g for year 2000:
1)Subtract 2: 2000-2=1998
2)MOD(1998, 19) = 3
3)Multiply *11: 3*11=33
4)MOD(33, 30) = 3
5)SUBTRACT FROM 44: 44-3=41
6)We start counting from March, so it is the 41 of March 2000 => 23 April 2000
7)Next Sunday of 23/04/2000 is 30/04/2000 which is the Easter day for 2000
SELECT
44-MOD(MOD((2000-2), 19)*11, 30)
FROM DUAL
Can you please assist me implementing step 6 in 9i ?
It must handle year e.g 2010 as well where the output till step 5 is 21 and we dont need to count over to the next month.
Thank you in advance

Answer 1

I tried it using the Meeus Julian algorithm
http://en.wikipedia.org/wiki/Computus
you could of course combine all the a b c d e stuff into one calculation but I left it alone for clarity
WITH years AS (    SELECT 1989 + LEVEL yr
                     FROM DUAL
               CONNECT BY LEVEL <= 30)
SELECT TO_CHAR (TO_DATE (day || ' ' || month || ' ' || yr, 'DD MM YYYY'),
                'DD MON YYYY')
          easter_day_julian,
       TO_CHAR (
          TO_DATE (day || ' ' || month || ' ' || yr, 'DD MM YYYY') + 13,
          'DD MON YYYY')
          easter_day_gregorian
  FROM (SELECT yr,
               a,
               b,
               c,
               d,
               e,
               FLOOR ( (d + e + 114) / 31) month,
               MOD (d + e + 114, 31) + 1 day
          FROM (SELECT yr,
                       a,
                       b,
                       c,
                       d,
                       MOD ( ( (2 * a) + (4 * b) - d + 34), 7) e
                  FROM (SELECT yr,
                               a,
                               b,
                               c,
                               MOD ( (19 * c + 15), 30) d
                          FROM (SELECT yr,
                                       MOD (yr, 4) a,
                                       MOD (yr, 7) b,
                                       MOD (yr, 19) c
                                  FROM years))))
EASTER_DAY_JULIAN     EASTER_DAY_GREGORIAN
02 APR 1990     15 APR 1990
25 MAR 1991     07 APR 1991
13 APR 1992     26 APR 1992
05 APR 1993     18 APR 1993
18 APR 1994     01 MAY 1994
10 APR 1995     23 APR 1995
01 APR 1996     14 APR 1996
14 APR 1997     27 APR 1997
06 APR 1998     19 APR 1998
29 MAR 1999     11 APR 1999
17 APR 2000     30 APR 2000
02 APR 2001     15 APR 2001
22 APR 2002     05 MAY 2002
14 APR 2003     27 APR 2003
29 MAR 2004     11 APR 2004
18 APR 2005     01 MAY 2005
10 APR 2006     23 APR 2006
26 MAR 2007     08 APR 2007
14 APR 2008     27 APR 2008
06 APR 2009     19 APR 2009
22 MAR 2010     04 APR 2010
11 APR 2011     24 APR 2011
02 APR 2012     15 APR 2012
22 APR 2013     05 MAY 2013
07 APR 2014     20 APR 2014
30 MAR 2015     12 APR 2015
18 APR 2016     01 MAY 2016
03 APR 2017     16 APR 2017
26 MAR 2018     08 APR 2018
15 APR 2019     28 APR 2019here it is combined
SELECT TO_CHAR (
          TO_DATE (
             (MOD (
                 (MOD ( (19 * (MOD (yr, 19)) + 15), 30))
                 + (MOD (
                       (  (2 * (MOD (yr, 4)))
                        + (4 * (MOD (yr, 7)))
                        - (MOD ( (19 * (MOD (yr, 19)) + 15), 30))
                        + 34),
                       7))
                 + 114,
                 31)
              + 1)
             || ' '
             || (FLOOR (
                    ( (MOD ( (19 * (MOD (yr, 19)) + 15), 30))
                     + (MOD (
                           (  (2 * (MOD (yr, 4)))
                            + (4 * (MOD (yr, 7)))
                            - (MOD ( (19 * (MOD (yr, 19)) + 15), 30))
                            + 34),
                           7))
                     + 114)
                    / 31))
             || ' '
             || yr,
             'DD MM YYYY'),
          'DD MON YYYY')
          easter_day_julianEdited by: pollywog on Nov 17, 2010 8:37 AM