Notes on the Orthodox Easter |
Notes on Feasts with fixed dates
in the Orthodox Calendar
The Orthodox Ecclesiastical Calendar
Last updated 2000 April 7 by
Between AD326 and AD1582, Christianity determined Easter using an
algorithm approved by a Church Council in AD325, with the equinox
defined as March 21. From AD1054 (when the Orthodox and Catholic Churches split)
through AD1582 both the Catholic and Orthodox Churches celebrated
Easter on the same date, still using the algorithm from AD325. The
Julian Calendar was used by the European (and Christan) communities
until the Gregorian reform of 1582.
Since AD1582 October (when the Gregorian Calendar was adopted by much
of Catholic Europe), the Orthodox Easter usually falls on dates
different than the Western Christian Easter, although apparently the
Churches are discussing using the same formula to determine Easter -
probably a formula different than that currently used by either
The Orthodox Easter is determined in the Julian Calendar. It has been
claimed that Orthodox Easter does not fall on the date of Passover (15
Nisan in the Hebrew Calendar), or before it; this is true recently, but
using the modern formulae for determining the date of Passover (rules
which go back to the fourth century A.D.), one finds that, in fact,
Easter occurred on the first day of Passover several times before the
year A.D. 1000. From 1900 until 2099 the Eastern Easter will fall one
(45.5%), four (4.5%), or five (21.5%) weeks after the Western Easter
- and on the same date in 57 (28.5%) of those years. (I've compiled some Tables showing the offsets between Orthodox
and Western Easters from 1583 through 3000 that shows this information.)
Calendar Reform in the Orthodox Church
In the 1923 May there was a well documented meeting that provided for
Reform in of the Orthodox Church. Among other measures, the
Orthodox Calendar would have been adjusted to match the Gregorian
calendar date; the proposed leap year rule was different than the rule in the
Gregorian Calendar, however the calendars would not disagree until
AD2800; more often than not, Easter would be celebrated on the same
date in both the Eastern and the Western Churches. Except for sporadic
use in the 1920's, the calendar reform was not adopted. A wonderful
resource examining the calendar reform and its lack of acceptance may
be found in the excellent article
Counter-reformation in Russian Orthodoxy: Popular Response to Religious
by Gregory L. Freeze that appeared in the Summer 1995
issue of Slavic Review. Freeze mentions that soon after
the adoption by the second (renovationist) council in 1923 May, the
renovationists had a full-scale parish revolt on their hands - the
common Orthodox parishioners (in the Soviet Union) did not accept the
changes of this council, and indeed, had many other arguements with the
renovationists. Other articles concerning Orthodox Calendar Reform
that may be found online are: 1) On the Question of the
"Revised Julian Calendar" by Father George Lardas; 2) The "Revised"
Julian Calendar which offers some explanation of the "New
Calendarist views"; and 3) On the Calendar by
Father Alexander Lebedeff, which argues for the "Old Calendarist"
Alex Kochergin has sent the following
information about the Eastern Easter: It has a cycle that (in the
Julian Calendar) repeats itself every 532 (19x28) years (since the
Julian Solar calendar repeats every 28 years and the Metonic Lunar
cycle is 19 years). Eastern Easter tends to occur only after Passover,
but only since about A.D 1000. The Gregorian Easter (on the other hand)
does not track Passover. For example: in 1997, Passover is 22 April;
Western Easter is three weeks EARLIER (30 March) and the Eastern Easter
is the Sunday following Passover (27 April). While there are obviously
different algorithms used, it is also the case the Julian, Gregorian,
and Jewish calendars are slipping relative to each other. The Julian
Calendar (and the feasts tied to it) are occuring later in the year
(compared to the Gregorian calendar). The Jewish calendar is also
moving to later dates in the Gregorian calendar, but at a
significantly slower rate than the Julian calendar.
The Date of Orthodox Easter: A variation of Gauss' algorithm
Alex also provided the following algorithm that is based on the algorithm
derived by the German mathematician Gauss, the principal simplification is
that substitutions have been made for the case of Julian calendars and
Orthodox Easters. This algorithm calculates the
number of days AFTER March 21 (Julian) that Easter occurs (Note: It is a
much simpler calculation than the Western Easter).
RMD(x,y) = remainder when x is divided by y.
The number RC ranges from 1 to 35 which corresponds to March 22 to April 25
in the Julian Calendar (currently April 4 to May 8 on the Gregorian). The
Julian Calendar is now 13 days behind the Gregorian, and will be until
March 1, 2100 when it will be 14 days behind the Gregorian Calendar.
The Date of Orthodox Easter: An algorithm based on Oudin's Algorithm
Another simple algorithm is listed in the Calendar
FAQ by Claus Tondering . It is based on
Oudin's algorithm, and is also simple and elegant.
Copyright and disclaimer
This document is Copyright (C) 1996 by Claus Tondering.
The document may be freely distributed, provided this
copyright notice is included and no money is charged for
This document is provided "as is". No warranties are made as
to its correctness.
2.9.6. Isn't there a simpler way to calculate [Orthodox] Easter?
This is an attempt to boil down the information given in the previous
sections (the divisions are integer divisions, in which remainders are
[Note: 22%7=1 ; 22/7=3, so % returns the remainder, and / neglects the
G = year % 19
I = (19*G + 15) % 30
J = (year + year/4 + I) % 7
L = I - J
EasterMonth = 3 + (L + 40)/44
EasterDay = L + 28 - 31*(EasterMonth/4)
[Note: Orthodox Easter is then EasterDay of EasterMonth in the Julian
Calendar. You will need to add the correct offset to obtain the
date in the Gregorian Calendar. From Julian Mar 1, 1900, to Julian
Feb 29, 2100, the correction is to add 13 days to the Julian date to
obtain the Gregorian date.]
This algorithm is based in part on the algorithm of Oudin (1940) and
quoted in "Explanatory Supplement to the Astronomical Almanac",
P. Kenneth Seidelmann, editor.
People who want to dig into the workings of this algorithm, may be
interested to know that
G is the Golden Number-1
I is the number of days from 21 March to the Paschal full moon
J is the weekday for the Paschal full moon (0=Sunday, 1=Monday,
L is the number of days from 21 March to the Sunday on or before
the Pascal full moon (a number between -6 and 28)
Using these algorithms, I have made tables for the date of Orthodox Easter,
tabulated in both the Julian and Gregorian calendars for AD 1875-2124.
Butcher's algorithm, and
Oudin's algorithm are algorithms for the Western
Movable Feasts Associated with Easter
The Ecclesiastical Calendar
uses the algorithm above to determine
the date of Easter. In addition, the following feasts related to Easter
are provided by the Ecclesiastical Calendar.
Days before Easter Days after Easter
Triodon 70 Ascension 39
Sat. of Souls 57 Sat. of Souls 48
Meat Fare 56 Pentecost 49
2nd Sat. of Souls 50 All Saints 56
Lent Begins 48
St. Theodore 43
Sun. of Orthodoxy 42
Sat. of Lazarus 8
Palm Sunday 7
Good Friday 2
Calculate an Ecclesiastical Calendar.
Notes on Feasts with Fixed Dates
The date of Fixed celebrations in the Orthodox calendar is made more
difficult by the fact that there are currently differing schools of thought
on whether to use the Gregorian or the Julian calendar to determine the
date of the Feasts that occur on fixed dates. The two schools of thought are
Calendarists" and the "New
in the Orthodox
The Old Calendarists use the Julian Calendar to determine the
date of ALL religious feasts. This means that Christmas and Epiphany
(for example) are
25 Dec. and 6 Jan. JULIAN, repectively. This (currently!)
translates to 7 Jan. and 19 Jan. Gregorian, respectively.
The New Calendarists use the Julian Calendar to determine the date
of Easter (and celebrations related to Easter) while using the
Gregorian calendar to determine the date of fixed celebrations. Thus
New Calendarists celebrate Christmas and Epiphany on the same date as the
Western Christians, Dec. 25 and 6 Jan. GREGORIAN (respectively). Currently,
the New Calendarists are celebrating the fixed feasts 13 days prior to the
celebrations of the Old Calendarists.
Special thanks to Alex Kochergin, John Cross, and Damien Wyart for
useful discussions concerning the content of this page, and to Claus
Tondering for maintaining and providing the Calendar FAQ. Please also
consult the Resources and Acknowledgements
section of the Ecclesiastical Calendar page.
Back to the Ecclesiastical calendar.
Disclaimer: The views and writings presented here are my own,
and are NOT the responsibility of Smart Net.
Last updated 2000 April 7.
Copyright © 1996-2000 by Marcos J. Montes.