Christmas
ORIGIN OF THE WORD
The word for Christmas in late Old English is Cristes Maesse, the Mass of Christ, first found in 1038, and Cristes-messe, in 1131. In Dutch it is Kerst-misse, in Latin Dies Natalis, whence comes the French Noël, and Italian Il natale; in German Weihnachtsfest, from the preceeding sacred vigil. The term Yule is of disputed origin. It is unconnected with any word meaning "wheel". The name in Anglo-Saxon was geol, feast: geola, the name of a month (cf. Icelandic iol a feast in December).
EARLY CELEBRATION
Christmas was not among the earliest festivals of the Church. Irenaeus and Tertullian omit it from their lists of feasts; Origen, glancing perhaps at the discreditable imperial Natalitia, asserts (in Lev. Hom. viii in Migne, P.G., XII, 495) that in the Scriptures sinners alone, not saints, celebrate their birthday; Arnobius (VII, 32 in P.L., V, 1264) can still ridicule the "birthdays" of the gods.
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Reform of the Calendar
The Year (Tropical Year) is the period in which the sun makes a complete circuit of the heavens and returns to the point in the zodiac whence it started, and the problem to be solved by those who construct calendars is to find the exact measure of this yearly period in terms of days, for the number of these occupied by the sun's annual journey is not exact. Taking the vernal equinox as a convenient starting-point, it is found that before the sun arrives there again, 365 days and something more have passed. These are, of course, solar days; of sidereal days, each shorter by four minutes, there are 366. The first attempt to find a practical solution of this problem was made by Julius Cæsar, who introduced the Julian Calendar. With the assistance of the astronomers of Alexandria, he determined the true length of the year to be 365 days and 6 hours, or a quarter of a day. From this it followed that the reckoning of the civil year began too soon, i.e. six hours before the sun had reached the point whence it started its annual cycle. In four years, therefore, the year would begin an entire day too soon. To remedy this Cæsar instituted leap-years, a 366th day being introduced in every fourth year, to cover the fractional portions of a day thus accumulated. This extra day was assigned to February, the 24th and 25th day of which were styled in leap-year the sixth before the calends (or first) of March. Hence the name Bissextile given to these years.
Cæsar's reform, which was introduced in the year 46 B.C., would have been perfect had the calculation on which it was based been accurate. In reality, however, the portion of a day to be dealt with, over and above the complete 365, is not quite six hours, but 11 minutes and 14 seconds less. To add a day every fourth year was, therefore, almost three quarters of an hour too much, the following new year commencing 44 minutes and 52 seconds after the sun had passed the equinox. At the end of a century these accumulated errors amounted to about three-quarters of a day, and at the end of four centuries to three entire days. The practical inconveniences of this defect in the system were not slow in making themselves felt, the more so as, Cæsar being murdered soon after (44 B.C.), leap-year, by a misunderstanding of his play, occurred every third year, instead of every fourth. At the time of the Julian reform the sun passed the vernal equinox on 25 March, but by the time of the Council of Nicæa (A.D. 325) this had been changed For the 21st, which was then fixed upon as the proper date of the equinox--a date of great importance for the calculation of Easter, and therefore of all the moveable feasts throughout the year.
But the error, of course, continued to operate and disturb such arrangements. In the thirteenth century the year was seven days behind the Nicæan computation. By the sixteenth it was ten days in arrear, so that the vernal equinox fell on 11 March, and the autumnal on 11 September; the shortest day was 11 December, and the longest 11 June, the feast of St. Barnabas, whence-the old rhyme:
Barnaby bright, the longest day and the shortest night.
Such alterations were too obvious to be ignored, and throughout the Middle Ages many observers both pointed them out and endeavoured to devise a remedy. For this purpose it was necessary, however, not only to determine with accuracy the exact amount of the Julian error, but also to discover a practical means of correcting it. It was this latter problem that chiefly stood in the way of reform, for the amount of error was ascertained almost exactly as early as the thirteenth century. The necessity of a reform was continually urged, especially by Church authorities, who felt the need in connexion with the ecclesiastical calendar. It was accordingly strongly pressed upon the attention of the pope by the councils of Constance, Basle, Lateran (A.D. 1511), and finally by Trent, in its last session (A.D. 1563).
Nineteen years later the work was accomplished by Pope Gregory XIII (from whom the Gregorian reform takes its name) with the aid chiefly of Lilius, Clavius, and Chacon or Chaconius. There were two main objects to be attained: first, the error of ten days, already mentioned, which had crept in, had to be got rid of; second, its recurrence had to be prevented for the future. The first was attained by the omission from the calendar of the ten superfluous days, so as to bring things back to their proper position. To obviate the recurrence of the same convenience, it was decided to omit three leap years in every four centuries, and thus eliminate the three superfluous days, which, as we have seen, would be introduced in that period under the Julian system. To effect this, only those Centurial years were retained as leap years the first two figures of which are exact multiples of 4--as 1600, 2000, 2400--other centurial years 1700, 1800, 1900, 2100, etc.--becoming common years of 365 days each. By this comparatively simple device an approximation to perfect accuracy was effected, which for all practical purposes is amply sufficient; for, although the length of the Gregorian year exceeds the true astronomical measurement by twenty-six seconds, it will be about thirty-five centuries before the result will be an error of a day, and, as Lord Grimthorpe truly says, before that time arrives mankind will have abundant time to devise a mode of correction.
For the actual introduction of the Gregorian Calendar or New Style, throughout Christendom, see CHRONOLOGY ...
http://www.newadvent.org/cathen/03738a.htm#gregorian
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