The Calendar by David Ewing Duncan Page B

                                 =      (b+ 8)/25
g                                 =      (b- f + 1)/3
h                                  =      (19 * a + b - d - g + 15)%30
i                                  -       c/4
k                                 =      c%4
l                                   =      (32 + 2*e + 2* i --h--k)%7
m                               =      (a + 11 * h + 22 * l )/451
Easter month          =      ( h + 1 - 7 * m + 114)/31 [3 = March, 4 = April]
    p                                 =      ( h + 1 -7 * »i + 114)%31
Easter date              =      p + 1 (date in Easter month)
    /                         =      division neglecting the remainder
%                       =      division keeping only the remainder
*                        =      multiply
    As far as anyone knows, the bishops at Nicaea did not officially assign anyone or anyplace to make the official Easter determination, though the task naturally fell to Alexandrian astronomers: Even before the great council, the bishops of Alexandria had dispatched letters to other churches announcing the date when they would celebrate the Easter feast. Few details are available about these early calculations, though the Alexandrians before and after Nicaea apparently used the old 19-year cycle of lunar months--the Metonic cycle--to link the moon to the solar year.
    The Alexandrians also seem to have been the ones who fixed the date for the spring equinox on 21 March, a change from Caesar’s day, when the equinox was set on 25 March. This shift may have been an attempt to compensate for the drift in Caesar’s calendar against the true solar year, though the true drift between Caesar’s reform in 45 BC and the Council of Nicaea in AD 325 was closer to three days than to four.
    At least two astronomers are known to have created time charts predicting future dates for Easter. Both were also bishops of Alexandria--Theophilus (bishop 385-412), whose tables covered a 100-year span between 380 and 480, and his nephew Cyrillus, who succeeded his uncle and devised a 95-year table covering the Easters between 437 and 531. Both charts were reasonably accurate, though they suffered from a small flaw in the Metonic cycle--the fact that 235 synodic lunar months do not fit exactly into 19 Julian years, falling one day long. Over the course of 95 years (five 19-year cycles) this excess of a single day amounts to a five-day mistake in matching up the phases of the moon with the Julian calendar--a problem early time reckoners attempted to deal with by intercalating a day into each 19-year cycle.
    A more serious problem for Easter reckoners after Nicaea was political rather than scientific. Not every city went along with the Alexandrians’ methods for dating Easter, despite the council’s dictate that the Easter question should be addressed uniformly for all Christians.
    The most pronounced difference was between the churches of the East, which followed Alexandria’s lead, and the churches of the West, which looked to Rome--a split that went far beyond issues of Easter and the calendar as the Roman world slowly divided itself along a fault line of East and West, Greek and Latin, Hellenistic and Roman. The Easter differences between Rome and Alexandria were small but important, particularly because they foreshadowed the eventual split between the Greek and Latin churches, which to this day celebrate Easter on different dates.
    The first East-West Easter squabble concerned dating the equinox. The Egyptians continued to use 21 March. Rome, however, used Caesar’s