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At the Orthodox Church Council in 1923 in Constantinople a proposal concerning the reform of the calendar, elaborated by the Serbian astronomer Milutin Milankovic´ together with professor Maksim Trpkovic´, was submitted, providing for a more exact calendar than the Gregorian one. Instead of three days in 4 centuries one should omit 7 days in 9 centuries or 0.0077 days per year. This means that only 2 years out of 9 ending the centuries would be leap years. The rule is that those years whose ordinal number ends with two zeros are leap years only provided that the number of centuries they belong to, divided by 9, yields the remainder 2 or 6. For instance the year 2000, ending the 20th century, is a leap year since 20 divided by 9 equals to 2 plus the remainder 2. Milankovic´'s proposal implies a much smaller difference, with respect to the true tropical year, than the Gregorian calendar. Further improvements concerning the approach to the duration of the tropical year are not necessary since that duration itself undergoes changes over longer periods.

Keywords: Calendar; Milankovic´; celestial mechanics

Document Type: Research Article


Affiliations: 1: Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia, Yugoslavia 2: Department of Astrophysics-Astronomy and Mechanics, School of Physics, University of Athens, Panepistimiopolis, Zographos 157 84, Athens-Greece

Publication date: 2002-01-01

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