Against the background of all the world events of the 16th and 17th centuries, when Byzantium collapsed, when the Orthodox Russian Empire grew and became stronger, when Western Europe underwent reformation, there occurred yet another event that had extremely important consequences.

Pope Gregory XIII, having been persuaded that the solar calendar was inaccurate and required correction, decided to correct the calendar with the help of his two Vatican astronomers. By means of a narrow ray of sunlight, which fell across the floor of the so-called “calendar room” in the Vatican, it was proven to the Pope that the real length of the tropical solar year is not 365 and a quarter days, as it is counted in the Julian calendar, but slightly less. In reality, the tropical solar year is equal to 365 days, 5 hours, 48 minutes, and approximately 46 seconds. In the Julian calendar it is counted as 365 days and precisely 6 hours.

Impressed by such obvious inaccuracy, the Pope decided to correct a calendar that had been working perfectly for over 1,200 years. In the Julian calendar each fourth year is a leap year, i.e. there are three consecutive years of 365 days each, while in the fourth year an extra day is added at the end of February (February 29th). In order to reduce the average length of the year and have it approximate the tropical year, the Pope decided to abolish some of the leap years.

In the Gregorian reform the leap year is abolished in those century years whose centuries are not exactly divisible by 400, i.e. 1700, 1800, 2100, 2200, etc. In the century years that are exactly divisible by 400, the leap years are not abolished, i.e. in 1600, 2000, 2400, etc. Aside from this “correction,” nothing has changed in relation to the Julian calendar, i.e. every fourth year (besides those mentioned above) is a leap year just as in the Julian calendar.

Why has this “correction” been made and to what has it led? Let us look at the explanation provided by Pope Gregory XIII himself in his famous papal bull Inter Gravissimas, issued on February 24, 1582. In it he says: “It has been our concern not only to restore the equinox to its erstwhile appointed place, from which it has moved approximately ten days from the time of the Nicean Council (325 A.D.), and to return to the 14th Moon is proper place, from which it currently digresses by four or five days, but also to establish means and rules by which it could be achieved that in the future the equinox and the 14th Moon would never move from their places.” It is hard to imagine that Pope Gregory XIII did not know that what he had expressed in his bull was, firstly, absolutely impossible, secondly – totally unnecessary, and thirdly – extremely detrimental.

All the prominent scientists of those times, including the great Copernicus, decisively refused to participate in preparing this Gregorian reform. It was sufficiently clear to everyone that the length of the day, the length of the year, and the length of the month are magnitudes that do not divide among themselves exactly. That is, the result of their mutual division, or their quotient, always produces an irrational number. Therefore, one cannot speak of absolute accuracy in the matter of the calendar. And to secure something forever, to make sure, for example, that the equinox and the 14th Moon would never move from their places, is mathematically absolutely impossible. Even in the Gregorian calendar the equinox still moves a whole 24 hours in the course of every three thousand years or so.

Furthermore, no calendar has an essential value per se. Every calendar is valued only for the convenience of its applicability. A calendar’s most important value lies in its practicality and not in its abstract “accuracy.” No calendar can be “accurate,” and the accuracy of all calendars is always only relative. Fortunately, this circumstance does not prevent a calendar from being useful and applicable. The calendar which Pope Gregory decided to correct had been quite useful for more than 1,200 years, while the Pope’s “correction,” though it gave the solar calendar an extra degree of relative accuracy, made it totally unfit for use in the Church.

The question arises: what was that ancient calendar like and in what way was it useful? That calendar was and is the church calendar. It is one of the greatest achievements of ancient astronomy and one of the most glorious masterpieces of calendrical science. One must note that the church calendar is not simply the Julian calendar, and it uses the Julian solar calendar only partially in order to intertwine into a single whole, firstly – the tropical solar year, secondly – the monthly course of the moon, and thirdly – the weekly circle of days. This interweaving into a single whole of three magnitudes that are indivisible among themselves is what precisely constitutes the church calendar and is called the “Paschalion” (or paschal cycle).

In this church calendar one cycle comprises 532 years and one such cycle is called the “Concordant Circle.” In this brilliant Concordant Circle all errors in the interrelation between the year, the month, and the day of the week are mutually cancelled out in the course of each cycle, so that at the end of one Concordant Circle and at the beginning of the next one the year, the month, the lunar phase, and the day of the week fall exactly on the same dates. In other words, every 532 years the church calendar begins anew at the same point.

From this point, where the dates of the year, the month, the lunar phase, and the day of the week coincide, the calendar once again unrolls through the course of 532 years, in order to return to the same exact point, only in a different time. This amazing cyclicity describes a wonderful spiral through time and, from the point of view of astronomy, leaves nothing better to be desired. This calendar is the only calendar that provides the opportunity for uninterrupted chronology both into the past and into the future. For this reason astronomy could never accept and will never be able to accept any other calendar, including, of course, the Gregorian one. It was, therefore, absolutely unnecessary and quite ludicrous to “correct” a calendar of such a degree of perfection.