Revised Julian calendar

The Revised Julian calendar, or less formally the new calendar and also known as the Milanković calendar, is a calendar proposed in 1923 by the Serbian scientist Milutin Milanković as a more accurate alternative to both Julian and Gregorian calendars. At the time, the Julian calendar was still in use by all of the Eastern Orthodox Churches and affiliated nations, while the Catholic and Protestant nations were using the Gregorian calendar. Thus, Milanković's aim was to discontinue the divergence between the naming of dates in Eastern and Western churches and nations. It was intended to replace the Julian calendar in Eastern Orthodox Churches and nations. From 1 March 1600 through 28 February 2800, the Revised Julian calendar aligns its dates with the Gregorian calendar, which had been proclaimed in 1582 by Pope Gregory XIII.

The Revised Julian calendar has been adopted for ecclesiastical use by the Ecumenical Patriarchate of Constantinople, the Orthodox Autocephalous Church of Albania, the Greek Orthodox Church of Alexandria, the Greek Orthodox Church of Antioch, the Bulgarian Orthodox Church, the Romanian Orthodox Church, the Cypriot Orthodox Church, the Church of Greece, the Orthodox Church of the Czech Lands and Slovakia, the Orthodox Church in America, the Orthodox Church of Ukraine, the Orthodox Church in Japan, and the Eastern Catholic Ukrainian Greek Catholic Church. It has not been adopted by the Russian Orthodox Church, the Serbian Orthodox Church, the Macedonian Orthodox Church, the Georgian Orthodox Church, the Polish Orthodox Church and the Greek Orthodox Patriarchate of Jerusalem. It has not been adopted by any nation as an official calendar. Instead, all of the Eastern Orthodox nations have adopted the Gregorian calendar as the official state calendar.

The Revised Julian calendar has the same months and month lengths as the Julian and Gregorian calendar, but, in the Revised Julian version, years evenly divisible by 100 are not leap years, except that years with remainders of 200 or 600 when divided by 900 remain leap years, e.g. 2000 and 2400 as in the Gregorian calendar.

Implementation
Comparison of Revised Julian and Gregorian calendar century years. (In the original Julian calendar, every century year is a leap year.)

A committee composed of members of the Greek government and Greek Orthodox Church was set up to look into the question of calendar reform. It reported in January 1923. In the end, for civil purposes, the Gregorian calendar was adopted; the changeover went into effect on 16 February/1 March.

After the promulgation of the royal decree, the Ecumenical Patriarch, Patriarch Meletius IV of Constantinople, issued an encyclical on 3 February recommending the calendar's adoption by Orthodox churches. The matter came up for discussion at the Council of Constantinople (1923), which deliberated in May and June. Subsequently, it was adopted by several of the autocephalous Orthodox churches. The synod was chaired by Meletius IV and representatives were present from the churches of Cyprus, Greece, Romania and Serbia. There were no representatives of the other members of the original Orthodox Pentarchy (the Patriarchates of Jerusalem, Antioch, and Alexandria) or from the largest Orthodox church, the Russian Orthodox Church.

The Serbian delegation presented a proposal by Maksim Trpković, which had a leap year rule in which century years would become common years, except those with remainders of 0 or 400 when divided by 900, which would remain leap years. However, it was rejected because the proposal would omit a leap year in 2000, which would cause it to differ from the Gregorian after only 77 years. Milanković proposed a small modification of Trpkovic's proposal, changing the timing of the century leap years to those with remainder 200 or 600 when divided by 900 in order to maximise the amount of time before it would differ from the Gregorian.

Milanković's arguments won the day. In its decision the conference noted that "the difference between the length of the political year of the new calendar and the Gregorian is so small that only after 877 years it is observed difference of dates." The same decision provided that the coming 1 October should be called 14 October, thus dropping thirteen days. It then adopted the leap year rule of Milanković. The proposed calendar was preferred over the Gregorian because its mean year was within two seconds of the then current length of the mean tropical year. The present vernal equinox year, however, is about 12 seconds longer, in terms of mean solar days.

The synod also proposed the adoption of an astronomical rule for Easter: Easter was to be the Sunday after the midnight-to-midnight day at the meridian of the Church of the Holy Sepulchre in Jerusalem (35°13′47.2″ E or UT+2$h$20$m$55$s$ for the small dome) during which the first full moon after the vernal equinox occurs. Although the instant of the full moon must occur after the instant of the vernal equinox, it may occur on the same day. If the full moon occurs on a Sunday, Easter is the following Sunday. Churches that adopted this calendar did so on varying dates. However, all Eastern Orthodox churches continue to use the Julian calendar to determine the date of Easter (except for the Finnish Orthodox Church, which now uses the Gregorian Easter; the Estonian Orthodox Church used the Gregorian Easter from 1923 to 1945).

Arithmetic
The following are Gregorian minus Revised Julian date differences, calculated for the beginning of January and March in each century year, which is where differences arise or disappear, until AD 10000. These are exact arithmetic calculations, not depending on any astronomy. A negative difference means that the proleptic Revised Julian calendar was behind the proleptic Gregorian calendar. The Revised Julian calendar is the same as the Gregorian calendar from 1 March 1600 to 28 February 2800, but the following day would be 1 March 2800 (RJ) or 29 February 2800 (G); this difference is denoted as '+1' in the table. 2900 is a leap year in Revised Julian, but not Gregorian: 29 February 2900 (RJ) is the same as 28 February 2900 (G) and the next day will be 1 March 2900 in both calendars - hence the '0' notation.

In 900 Julian years there are $900/4$ = 225 leap days. The Revised Julian leap rule omits seven of nine century leap years, leaving 225−7 = 218 leap days per 900-year cycle. Thus the calendar mean year is 365 + $218/900$ days, but this is actually a double-cycle that reduces to 365 + $109/450$ = 365.24$\overline{2}$ days, or exactly 365 days 5 hours 48 minutes 48 seconds, which is exactly 24 seconds shorter than the Gregorian mean year of 365.2425 days, so in the long term on average the Revised Julian calendar pulls ahead of the Gregorian calendar by one day in 3600 years.

The number of days per Revised Julian cycle = 900 × 365 + 218 = 328,718 days. Taking mod 7 leaves a remainder of 5, so like the Julian calendar, but unlike the Gregorian calendar, the Revised Julian calendar cycle does not contain a whole number of weeks. Therefore, a full repetition of the Revised Julian leap cycle with respect to the seven-day weekly cycle is seven times the cycle length = 7 × 900 = 6300 years.

March equinox
The following is a scatter plot of actual astronomical northward equinox moments as numerically integrated by SOLEX 11 using DE421 mode with extended (80-bit) floating point precision, high integration order (18th order), and forced solar mass loss ("forced" means taken into account at all times). SOLEX can automatically search for northern hemisphere spring equinox moments by finding when the solar declination crosses the celestial equator northward, and then it outputs that data as the Terrestrial Time day and fraction of day relative to 1 January 2000 at noon (J2000.0 epoch). The progressive tidal slowing of the Earth rotation rate was accounted for by subtracting ΔT as calculated by the Espenak-Meeus polynomial set recommended at the NASA Eclipses web site to obtain the J2000.0-relative Universal Time moments, which were then properly converted to Revised Julian dates and Jerusalem local apparent time, taking local apparent midnight as the beginning of each calendar day. The year range of the chart was limited to dates before the year AD 4400: by then ΔT is expected to accumulate to about six hours, with an uncertainty of less than $2 1/2$ hours.



The chart shows that the long-term equinox drift of the Revised Julian calendar is quite satisfactory, at least until AD 4400. The medium-term wobble spans about two days because, like the Gregorian calendar, the leap years of the Revised Julian calendar are not smoothly spread: they occur mostly at intervals of four years but there are occasional eight-year gaps (at 7 out of 9 century years). Evidently each of the authorities responsible for the Gregorian and Revised Julian calendars, respectively, accepted a modest amount of medium-term equinox wobble for the sake of traditionally perceived leap rule mental arithmetic simplicity. Therefore, the wobble is essentially a curiosity that is of no practical or ritual concern.

Adoption
The new calendar has been adopted by Orthodox churches as follows:


 * 1920: In Finland Orthodox faithful began attending Lutheran churches on holy days
 * October 1921 Finland officially switched to the Gregorian calendar, including the Gregorian Paschalion
 * 1923: Estonia (accepted the Gregorian calendar, including the Gregorian Paschalion, but in 1945 joined the Moscow Patriarchate and reverted to Julian; after re-establishing in 1996, the Estonian Apostolic Orthodox Church adopted the Revised Julian calendar in 2012)
 * 10/23 March 1924: Constantinople, Cyprus and Greece
 * 1/14 October 1924: Poland (Very few parishes changed - on 15 June 2014 the Church switched back, but individual parishes may use the Revised Julian calendar if they wish)
 * 1/14 October 1924: Romania
 * 1/14 October 1928: Alexandria and Antioch
 * The Albanian Orthodox Church became autocephalous on 12 April 1937
 * 20 December 1968: Bulgaria
 * 1 September 2023: Orthodox Church of Ukraine

Adopting churches are known as New Calendarists. The new calendar has not been adopted by the Orthodox churches of Georgia, Jerusalem, Macedonia, Mount Athos, Russia, Serbia, Ukrainian Orthodox Church (Moscow Patriarchate) (status is not defined), nor by the Greek Old Calendarists.

There were attempts to introduce Revised Julian as a religious calendar in the Soviet Union. On 12 June 1923, it was accepted by the short-lived schismatic Renovationist Church, which had seized church buildings with the support of the Soviet government while Patriarch Tikhon was under house arrest. After his release, on 15 July 1923, he declared that all Renovationist decrees were without grace. On 15 October 1923, Patriarch Tikhon accepted the new calendar, but it caused  disagreement among clergy, and 24 days later he reverted the decision. The present Russian Orthodox Church continues to use the Julian calendar for both its fixed festivals and for Easter.

Defense
The basic justification for the new calendar is the known errors of the Julian calendar, which will in the course of time lead to a situation in which those following the Julian calendar (in the Northern Hemisphere) will be reckoning the month of December (and the feast of Christ's Nativity) during the heat of summer, August and its feasts during the deep cold of winter, Easter during the autumn season, and the November feasts in the springtime. This would conflict with the Church's historic practice of celebrating Christ's birth on 25 December, a date chosen for a number of reasons. One of the reasons mentioned by Bennet is the time of the winter solstice, when the days begin to lengthen again as the physical sun makes its reappearance, along with the fact that Christ has traditionally been recognized by Christians as the metaphorical and spiritual sun who fulfills Malachi's prophetic words: "the sun of righteousness will shine with healing in its wings" (Malachi 4:2). The identification, based on this prophecy, of Jesus Christ as the "sun of righteousness" is found many times in writings of the early Church fathers and follows from many New Testament references linking Jesus with imagery of sun and light.

Criticism
Critics see the change in calendar as an unwarranted innovation, influenced by Western society. They say that no sound theological reason has been given for changing the calendar, that the only reasons advanced are social. The proposal for change was introduced by Meletios Metaxakis, Ecumenical Patriarch of Constantinople, a patriarch whose canonical status has been disputed.

The argument is also made that since the use of the Julian calendar was implicit in the decision of the First Ecumenical Council at Nicaea (325), which standardized the calculation of the date of Easter, no authority less than an Ecumenical Council may change it. It is further argued that the adoption of the new calendar in some countries and not in others has broken the liturgical unity of the Eastern Orthodox churches, undoing the decision made by the council of bishops at Nicaea to decree that all local churches celebrate Easter on the same day. The emperor Constantine, writing to the bishops absent from the council to notify them of the decision, argued, "Think, then, how unseemly it is, that on the same day some should be fasting whilst others are seated at a banquet".

Liturgical objections to the new calendar stem from the fact that it adjusts only those liturgical celebrations that occur on fixed calendar dates, leaving all of the commemorations on the moveable cycle on the original Julian calendar. This upsets the harmony and balance of the liturgical year. (This would not have been a problem if the recommendations of the 1923 synod to use an astronomical rule to reckon the date of Easter, as outlined above, had not been rejected.) This disruption is most noticeable during Great Lent. Certain feast days are designed to fall during Lent, such as the feast of the Forty Martyrs of Sebaste. The Feast of the Annunciation is also intended to fall either before Easter or during Bright Week. Sometimes, Annunciation will fall on the day of Easter itself, a very special concurrence known as Kyrio-Pascha, with special liturgical practices appointed for such an occurrence. However, under the new calendar, Kyrio-Pascha becomes an impossibility. The Apostles' Fast displays the most difficult aspect of the new calendar. The fast begins on the moveable cycle and ends on the fixed date of 29 June; since the new calendar is 13 days ahead of the traditional Julian calendar, the Apostles' Fast is 13 days shorter for those who follow the new calendar, and some years it is completely abrogated. Furthermore, critics of the new calendar point out the advantage to celebrating Nativity separately from the secular observances of Christmas and New Year, which are associated with partying and alcohol consumption.

Critics also point out that proponents of the new calendar tend to use worldly rather than spiritual justification for changing the calendar: wanting to "party with everyone else" at Christmas; concern that the gradual shift in the Julian calendar will somehow negatively affect the celebration of feasts that are linked to the seasons of the year. However, opponents counter that the seasons are reversed in the southern hemisphere, where the liturgical celebrations are no less valid. The validity of this argument is questionable, since the feasts of the Orthodox Church were not changed no matter where they were celebrated, and Orthodox services were held in the southern hemisphere with little issue centuries before the introduction of the new calendar.

From a spiritual perspective, Old Calendarists also point to a number of miraculous occurrences that occur on the old calendar exclusively, such as the "descent of the cloud on the mount" on the feast of the Transfiguration. After the calendar change was instituted, the followers of the old calendar in Greece apparently witnessed the appearance of a cross in the sky, visible to thousands on the feast of the Exaltation of the Holy Cross, 1925, of which eyewitness accounts were recorded.