The Encyclopedia Americana (1920)/Calendar

CALENDAR, a system of dividing time into years, months, weeks and days for use in civil life, or a register of these or similar divisions. Among the old Romans, for want of such a register, it was the custom of the pontifex maximus, on the first day of the month, which began with the new moon, to proclaim (calare) the month, with the festivals occurring in it. Hence, calendæ (the first of the month) and calendar. The periodical occurrence of certain natural phenomena gave rise to the first division of time. The apparent daily revolution of the sun about the earth occasioned the division into days. The time at which a day begins and ends has been differently fixed, the reckoning being from sunrise to sunrise, from sunset to sunset, from noon to noon, or from midnight to midnight. The changes of the moon, which were observed to recur every 29 or 30 days, suggested the division into months, but the month now used, though nearly equal to a lunation, is really an arbitrary unit; and, as a still longer measure of time was found necessary for many purposes, it was supplied by the apparent yearly revolution of the sun round the earth, producing the changing seasons. The time of this revolution is now known to be 365 days, 5 hours, 48 minutes and 46 seconds, but as it has at various times been reckoned differently, this has given rise to corresponding changes in the calendar. This unit of time is called a solar year. The division into weeks, which has been almost universally adopted, is not founded on any natural phenomenon, and, as it originated in the East, has been attributed to the divine command to Moses in regard to the observation of the seventh day as a day of rest. By other authorities it has been ascribed to the number of the principal planets, a theory supported by the names given to the days. It was not used by the Greeks, nor by the Romans, till the time of Theodosius. The great influence of the sun's course upon the seasons naturally attracted the attention of men at all periods to this phenomenon; accordingly all nations in any degree civilized have adopted the year as the longest unit of time. The year of the ancient Egyptians was based on the changes of the seasons alone, without reference to the lunar month, and contained 365 days, which were divided into 12 months of 30 days each, with five supplementary days at the end of each year. The Jewish year consisted of lunar months, of which they reckoned 12 in the year, intercalating a 13th when necessary to maintain the correspondence of the particular months with the regular recurrence of the seasons. The Greeks in the earliest period also reckoned by lunar and intercalary months. They divided the month into three decades, a system also adopted long afterward at the time of the French Revolution. It possesses the advantage of making the smaller division an exact measure of the larger, and under it the number of a day in the 10-day period readily suggests its number in the month. The Greeks in the time of Solon had a year of 12 months alternately of 29 and 30 days, the total number of days being 354, and the year being very nearly equal to a lunar one. Soon afterward a month of 30 days began to be intercalated every other year in order to reconcile their year with that founded on the sun's movement, but as the error was still very large the intercalary month was afterward omitted once in four times. The Jewish and also the Greek year thus both varied in duration according as the intercalary month was introduced or omitted. This, with the uncertainty as to the exact duration of the year, was a constant source of confusion.

Various plans for the reformation of the calendar were proposed from time to time; but all proved insufficient till Meton and Euctemon finally succeeded in bringing it to a much greater degree of accuracy by fixing on the period of 19 years, in which time the new moons return upon the same days of the year as before (as 19 solar years are very nearly equal to 235 lunations). (See Cycle). This mode of computation, first adopted by the Greeks about 432 B.C., was so much approved of that it was engraven with golden letters on a tablet at Athens. Hence the number showing what year of the moon's cycle any given year is is called the golden number. This period of 19 years was found, however, to be about six hours too long. This defect Calippus, about 102 years later, endeavored to remedy, but still failed to make the beginning of the seasons return on the same fixed day of the year.

The Romans first divided the year into 10 months, but they early adopted the Greek method of lunar and intercalary months, making the lunar year consist of 354, and afterward of 355 days, leaving 10 or 11 days and a fraction to be supplied by the intercalary division. This arrangement, which was placed under the charge of the pontiffs, continued until the time of Cæsar. The first day of the month was called the calends. In March, May, July and October, the 15th, in other months the 13th, was called the ides. The ninth day before the ides (reckoning inclusive) was called the nones. The other days of the months they reckoned forward to the next calends, nones, or ides, whether in the same or the succeeding month, always including both days in the reckoning. Thus the 3d of March, according to the Roman reckoning would be the fifth day before the nones, which in that month fell on the 7th. The 8th of January, in which month the nones happen on the 5th, and the ides on the 13th was called the 6th before the ides of January. Finally to express any of the days after the ides, they reckoned in a similar manner from the calends of the following month. From the inaccuracy of the Roman method of reckoning it appears that in Cicero's time the calendar brought the vernal equinox almost two months later than it ought to be. To check this irregularity Julius Cæsar invited the Greek astronomer Sosigenes to Rome, who, with the assistance of Marcus Fabius, invented that mode of reckoning which, after him who introduced it into use, has been called the Julian calendar. The chief improvement consisted in restoring the equinox to its proper place in March. For this purpose two months were inserted between November and December, so that the year 707 (46 B.C.), called from this circumstance the year of confusion, contained 14 months. In the number of days the Greek computation was adopted, which made it 365¼. The number and names of the months were kept unaltered with the exception of Quintilis, which was henceforth called, in honor of the author of the improvement, Julius. To dispose of the quarter of a day it was determined to intercalate a day every fourth year between the 23d and 24th of February. This was called an intercalary day, and the year in which it took place was called an intercalary year, or, as we term it, a leap year.

This calendar continued in use among the Romans until the fall of the empire, and throughout Christendom till 1582. The festivals of the Christian Church were determined by it. With regard to Easter, however, it was necessary to have reference to the course of the moon. The Jews celebrated Easter (that is, the Passover) on the 14th of the month Nisan (or March); the Christians in the same month, but always on a Sunday. Now, as the Easter of the Christians sometimes coincided with the Passover of the Jews, and it was thought unchristian to celebrate so important a festival at the same time as the Jews did, it was resolved at the Council of Nice, 325 A.D., that from that time Easter should be solemnized on the Sunday following the first full moon after the vernal equinox, which was then supposed to take place on 21 March. As the course of the moon was thus made the foundation for determining the time of Easter, the lunar Cycle of Meton whs taken for this purpose; according to which the year contains 365¼ days, and the new moons, after a period of 19 years, return on the same day as before. The inaccuracy of this combination of the Julian year and the lunar cycle must have soon discovered itself on a comparison with the true time of the commencement of the equinoxes, since the received length of 365¼ days exceeds the true by about 11 minutes; so that for every such Julian year the equinox receded 11 minutes, or a day in about 130 years. In consequence of this, in the 16th century, the vernal equinox had changed its place in the calendar from the 21st to the 10th; that is, it really took place on the 10th instead of the 21st, on which it was placed in the calendar. Luigi Lilio Ghiraldi, frequently called Aloysius Lilius, a physician of Verona, projected a plan for amending the calendar, which, after his death, was presented by his brother to Pope Gregory XIII. To carry it into execution, the Pope assembled a number of prelates and learned men. In 1577 the proposed change was adopted by all the Catholic princes; and in 1582 Gregory issued a brief abolishing the Julian calendar in all Catholic countries, and introducing in its stead the one now in use, under the name of the Gregorian or reformed calendar, or the new style, as the other was now called the old style. The amendment ordered was this: 10 days were to be dropped after 4 Oct 1582, and the 15th was reckoned immediately after the 4th. Every 100th year, which by the old style was a leap year, was now to be a common year, the 4th century divisible by four excepted; that is, 1600 was to remain a leap year, but 1700, 1800, 1900 of the common length, and 2000 a leap year again. In this calendar the length of the solar year is taken to be 365 days, 5 hours, 49 minutes and 12 seconds, the difference between which and the true length is immaterial. In Spain, Portugal and the greater part of Italy the amendment was introduced according to the Pope's instructions. In France the 10 days were dropped in December, the 10th being called the 20th. In Catholic Switzerland, Germany and the Netherlands the change was introduced in the following year, in Poland in 1586, in Hungary 1587. Protestant Germany, Holland and Denmark accepted it in 1700, and Switzerland in 1701, In the German empire a difference still remained for a considerable time as to the period for observing Easter. In England the Gregorian calendar was adopted in 1752, in accordance with an act of Parliament passed the previous year, the day after 2d September becoming the 14th, Sweden followed in 1753. Russia and Greece still adhere to the Julian calendar, which, by the interjection of two more days, 1800 and 1900 being regarded as leap years, now differs from the Gregorian calendar by 13 days. Thus 14 Jan. 1917 of the new style will be 1 Jan. 1917 in Greece and Russia.

The change adopted in the English calendar in 1752 embraced another point. There had been previous to this time various periods fixed for the commencement of the year in various countries of Europe. In France, from the time of Charles IX, the year was reckoned to begin from 1 January; this was also the popular reckoning in England, but the legal and ecclesiastical year began on 25 March. The 1st of January was now adopted as the beginning of the legal year, and it was customary for some time to give two dates for the period intervening between 1 January and 25 March, that of the old and that of the new year, as January 1752-53.

In France, during the Revolutionary epoch, a new calendar was introduced by a decree of the National Convention, 24 Nov. 1793. The new reckoning was to begin with 22 Sept 1792, the day on which the first decree of the new republic had been promulgated. The year was made to consist of 12 months of 30 days each, and, to complete the full number, five fête days (in leap year six) were added at the end of the year. Instead of weeks, each month was divided into three parts, called decades, consisting of 10 days each; the other divisions being also accommodated to the decimal system. This calendar was abolished at the command of Napoleon, by a decree of the Senate, 9 Sept. 1805, and the common or Gregorian calendar was re-established on 1 January of the following year. The Mohammedans employ a lunar year of 354 days and 12 lunar months, which have alternately 29 and 30 days. Thirty years form a cycle and 11 times in every cycle an extra day is added at the end of the year. The months and the seasons do not correspond and the first of the year may fall at any time during the solar year. The months are named Muharram, Saphar, Rabia I, Rabia II, Jomadi I, Jomadi II, Rajah, Shaaban, Ramadan, Shawall, Dulkaada and Dulkeggia. The Mohammedan era is computed from the first day of the year of the Hejira, or flight of Mohammed to Medina. It corresponds with 15 July 622 of the Christian era. The Mohammedan year which began on 28 Oct. 1916 was the 15th year of the 45th cycle, or the year 1335 of the Mohammedan era. See also Chronology; Cycle; Epoch; Hejira.

Bibliography. — Boll, ‘Griechisches Kalendar’ (Heidelberg 1910); Bowditch, ‘Numeration, Calendar Systems and Astronomical Knowledge of the Mayas’ (Cambridge, Mass., 1910); Burnaby, ‘Elements of the Jewish and Mohammedan Calendar’ (London 1901); Langdon, ‘Tablets from the Archives of Drehem, with a Complete Account of the Origin of the Sumerian Calendar’ (Paris 1911); Mahler, ‘Etudes sur le calendrier égyptien’ (ib. 1907); Plunket, ‘Ancient Calendars and Constellations’ (London 1903); Schram, ‘Kalendariographische und chronologische Tafeln’ (Leipzig 1908).