Revised Julian Calendar

The Revised Julian Calendar was proposed by the Serbian scientist Milutin Milanković, an expert in astronomy and geophysics, at a synod convened by the Eastern Orthodox Church in Constantinople. The motivation behind this reform was to correct the slight inaccuracy in the Gregorian leap year system, which overestimates the length of the solar year by about 0.0003 days per year.

The Gregorian Calendar, while an improvement over the Julian Calendar, still had a minor discrepancy: it calculates the solar year to be 365.2425 days, slightly longer than the actual solar year of approximately 365.2422 days. This difference means that the Gregorian Calendar gains about one day every 3,225 years compared to the solar year.

To address this, the Revised Julian Calendar modifies the leap year formula of the Gregorian Calendar. Like the Gregorian system, it includes a leap day in years divisible by four. However, it omits the leap day in centennial years (those ending in 00), except if the year number is divisible by 900 and leaves a remainder of 200 or 600 when divided by 900. This makes the average year length very close to the actual solar year — 365.2422 days.

The Revised Julian Calendar was initially adopted by some Eastern Orthodox churches to calculate the date of Easter and other fixed and movable feasts. Its adoption varied among different Orthodox communities. Some adopted it immediately, while others continued to use the Julian Calendar, leading to variations in the observance of religious dates among Orthodox Christians.

One of the significant features of the Revised Julian Calendar is that it aligns closely with the Gregorian Calendar for many centuries. When it was introduced in 1923, it was in complete agreement with the Gregorian Calendar. The first divergence between the two will occur in the year 2800, when the Revised Julian Calendar will not have a leap day, but the Gregorian Calendar will.

The calendar consists of the familiar twelve months, starting with January and ending with December. The lengths of these months are the same as in the Gregorian Calendar, ensuring that for the time being, both calendars remain largely indistinguishable in everyday use.

The impact of the Revised Julian Calendar has been primarily within the context of the Eastern Orthodox Church. It has facilitated a more astronomically accurate way of determining ecclesiastical dates. However, its use for civil purposes has been limited, with the Gregorian Calendar remaining the predominant system globally.

In terms of cultural and societal impact, the Revised Julian Calendar demonstrates the ongoing human endeavor to measure time with greater precision. It reflects an understanding that even small inaccuracies in timekeeping can accumulate over long periods, necessitating periodic adjustments and reforms.