Home Page for
Calendar Reform

date in the
Gregorian Calendar:

The time is out of joint; O cursed spite,
That ever I was born to set it right!


Gregory's Contribution
by Elisabeth Achelis, Journal of Calendar Reform, June 1954

AFTER CONSTANTINE, 1250 years passed before another changed in the calendar occurred. In 1582 Pope Gregory XIII undertook the revision now in general use.

In the intervening medieval centuries (between the fifth and sixteenth) a number of important events had a lasting impact upon Western civilization. The reign of Charlemagne in the eighth and ninth centuries brought together in a new unity many of the Northern peoples of Europe. The Arabic contributions to the West in the fields of science, mathematics, art and education reached their peak in the tenth century. The Norman invasion in the eleventh century forced the islanders of Great Britain into the European arena. The eight Crusades between the eleventh and thirteen centuries gave Europe a closer contact with the Near East. The Magna Carta of the thirteenth century freed Englishmen from feudal lords and barons. The Gutenberg printing press of the fifteenth century led to a broader dissemination of learning. The discovery of America in the fifteenth century stimulated almost every phase of human activity in the Old World. The Reformation of the sixteenth century lifted men's conscience the domination of state religions. Everywhere there were driving forces urging mankind forward toward new freedoms, broader knowledge and greater unity.

The calendar of Caesar and Constantine, with its irregularities and deficiencies, could not escape these forces. As early as the thirteenth century scholars and public officials complained that the calendar year was drifting away from the seasons, because under Caesar's four-year rule too many leap years had been inserted. The resultant difficulties were repeatedly called to the attention of rulers and popes, but nothing was done until the latter years of Gregory's occupancy of the pontifical throne.

The aging Pope, weary of wars and public works and financial difficulties, turned his attention at last to the calendar. Aided by a notable staff of scientists, he analyzed the problems. First, how could the year be brought back into accord with the seasons? Second, how could the leap-year rule be corrected to stop further dislocation? Third, could the beginning of the year be set in a fixed position, instead of being observed at different times by different peoples? Fourth, could anything be done about the wandering Easter, a cause of considerable inconvenience?

The Easter question was actually the source of the Papal investigation. Easter was a spring festival, but the "drifting" of the calendar had been gradually pushing it further and further away from the spring equinox. Eventually, if not corrected, Easter would be arriving in the winter, and this would correspondingly dislocate all the other important feasts which depend on it. Julius Caesar had kept the equinox on the ancient date of March 25; in Gregory's time it was falling on the 11th.

The error in Caesar's leap-year rule was readily understood. The Roman Emperor had figured the solar year at 365-1/4 days. Actually, it takes the earth but 365 days, 5 hours, 48 minutes and 46 seconds to complete its annual journey around the sun. The true year is thus 11 minutes and 14 seconds short of six hours—a quarter of the 24-hour day. This slight difference, accumulating through the centuries, had been sufficient to put the calendar 14 days off balance with the seasons.

Pope Gregory and his scientists decided to deal with the first of their four calendar problems by dropping a certain number of days from the year 1582. On the question of "How many days?" they worked out a compromise. Not the full 14 which would have brought things back to Caesar's formula, but only ten days, which adjusted the equinoctial date to march 21, where it had been observed at the time of the first Christian conclave at Nicea in A. D. 325. The use of Nicea as a starting point gave an ecclesiastical touch to the whole operation.

As to Problem Number Two, the new leap-year rule, skillfully formulated by the Pope's advisers, related only to century years. Those which were divisible by 400 were to be leap years; all the others were to be ordinary years, such as 1700, 1800, 1900. The years 1600 and 2000 are leap years. Outside of centurial years, all the other years keep to the simple four-year rule as prescribed by Caesar. Thus three leap years are dropped out of each 400 years, and this simple formula will keep the calendar approximately correct with the seasons for about 3,300 years from the time of the Gregorian Reform.

Problem Number Three was concerned with a stable New Year's Day. For many centuries, the New Year had been the most wayward of anniversaries. Julius Caesar had accepted January 1, but in the sixth century the Church had adopted March 25, the Feast of the Annunciation, which mystically recalled the birth of Christ. During succeeding centuries, this was a widely observed date, although all kinds of variations occurred from time to time. Germany and Spain thought the year should begin at Christmas, Denmark used an August New Year's Day, France and the Netherlands observed Easter. In Venice the date was March 1, in Ireland February 1.

To remove all the confusion Pope Gregory came out firmly for January 1. He ignored the pagan origin of this date, and gave it ecclesiastical standing by pointing out that it was the Feast of Circumcision in the church calendar. His scientific advisers probably reminded him that the first of January had a certain astronomical basis: the "perihelion" occurs on or about the beginning of January, when the earth is closest to the sun—being 91,500,000 miles away, as against 95,000,000 miles six months later.

Then there was the question of stabilizing Easter. The wandering character of Easter is due to the fact that it is tied to a lunar reckoning; theoretically Easter comes on the first Sunday after the full moon following the spring equinox. Here is a basic contradiction. The civil calendar goes by the sun; the religious feast day Easter is reckoned by the moon. No compromise is possible, for the result must be either one thing or the other.

There appears to be no reason why Easter cannot be observed on the Sunday nearest to the historical date of the Resurrection, presumably April 9. Gregory and his advisers attempted no such change. They left Easter as it was, and the result is a wandering festival which causes great inconvenience in countries where Easter is important in civil life.

The Gregorian revision went into effect in 1582 in all Roman Catholic countries. Then days where dropped from October: Thursday, October 4, was followed by Friday, October 15.

Outside the strictly Roman Catholic countries, there were long delays in recognizing the scientific advantages of Gregory's proposals. Protestant Germany and Denmark adopted the new calendar in 1700, Great Britain and the American colonies in 1752, Sweden in 1753, Japan in 1873, China in 1912. Russia and the Eastern Orthodox countries were tardiest of all—Russian first in 1918 and again in 1940 after experimenting with calendars of her own; and the Eastern Orthodox countries in 1924 and 1927.

The hesitance of the Northern nations to accept the Gregorian reform was due to the violent religious prejudices aroused by the Reformation. In the Eastern Orthodox area, too, the scientific nature of the reform was minimized and the priesthood feared that acceptance would be interpreted as a quasi-allegiance to a faith different from their own.

In other parts of the world, particularly in the Asiatic countries, the new system was labelled the "Christian Calendar" and its name created resistance among Hindus, Moslems, Buddhists, Taoists and other powerful groups.

These unfortunate reactions had not been foreseen by Gregory XIII and his advisers, who had expected that the revision would be accepted as a sound scientific action without religious connotations. It did now work that way. For more than a century, his calendar was help up as a symbol of Papal domination, and this caused the Roman Catholic Church a considerable amount of annoyance and trouble. It is one of the reasons, in the present age, that the Vatican—although in favor of revision—has been reluctant to take an initiative in the movement for a further improvement in the calendar.

The Gregorian reform was good up to a point. It anchored the calendar in the seasonal year from which it never should have strayed, and it established a uniform practice as to the year's beginning. It failed, however, to correct Caesar's faulty arrangement of the months, quarters and half years; and it did nothing to harmonize the wandering weekdays which were an inheritance from Constantine. These two faults are becoming increasingly burdensome with the development of civilization and the requirements of our modern world.

Gregory's able scientific advisers undoubtedly pointed out these defects. Such competent men as Lilius, Clavius and Scalliger could not have failed to realize the situation. The Pope's viewpoint, however, was strongly ecclesiastical: his primary concern was to make certain that he inconveniences of the church calendar were remedied, and he may have felt that any further action would endanger the simpler program he had in mind.

The Gregorian reform left the calendar still inadequate. There was no regularity in the arrangement of the months; the quarter years varied from 90 to 92 days in length; the half years were ridiculously unequal. The people actually had to use 14 different calendars and 28 different kinds of months. A new calendar had to be prepared and printed every year. The order, stability and comparability which only come when the year is one complete unit, such as the Egyptians and Julius Caesar recognized, were totally absent. The ideal of a perpetual and balanced measuring system of Time had to wait until the present twentieth century, when the pressures of science, business and a need for world unity would make imperative a further scientific simplification and perfection of the civil calendar.

It is a remarkable historic coincidence that at the very time when Gregory was wrestling with European calendar problems, the same sort of thing was happening in India. That then faraway country was enjoying the beneficent rule of Akber, greatest of the Mogul (Mongol) emperors and one of the most eminent royal personalities of all time. Much of his work of consolidation and organization in India survives to this day—and part of it involved an effort at unifying the Indian calendars.

Although Akber was unquestionably the greatest world figure of his century, he had to live within his limitations. One of these was that he knew practically nothing about the Western world except through a few contacts with Jesuit missionaries. His religion was a narrow form of Mohammedanism, which was a minority sect in India—even then a kaleidoscope of religions. In searching for an improved calendar, he never thought of consulting Europe and probably never heard of the Gregorian reform of 1582. Instead, he turned to Persia and its Jelali solar calendar, which he brought to India in 1584. It was one of the best of all solar calendars, with an even better approximation of the actual astronomical year than the Gregorian system.

Unfortunately Akber's reform measure was misunderstood, and after his death, in the absence of any central guidance, it became combined with ancient errors and local variations. Thus his main purpose of providing a national calendar was defeated. But it was a worthy attempt, and the broad vision which inspired it has always been recognized in India, and is indeed the foundation for the present movement under Nehru's leadership.

The world of today would be a better world had Akber and Pope Gregory joined forces in the 1580's. They would have emerged with a world-wide calendar, which would have drawn together the East and the West. The result would have been a powerful vehicle for international cooperation and understanding, qualities which remove narrow sectarianism and isolationist nationalism.

(Weekday arrangement varies each year)


First Quarter

31 days
28 or 29 days
31 days
90 or 91 days


Third Quarter

31 days
31 days
30 days
92 days


Second Quarter

30 days
31 days
30 days
91 days

Fourth Quarter

31 days
30 days
31 days
92 days

(First half year 181 or 182 days; second half year 184 days)


Home Page for
Calendar Reform