EPACTS AND NEW MOONS.
The Epact (Greek [Greek: epaktos] from [Greek: eapgo] I add) is nothing more than the number of days by which the common solar year of 365 days exceeds the common lunar year of 354 days. So that the epact of the first year is 11, because the common solar year exceeds the common lunar year by 11 days, and these added to the 11 days of the first, produce 22 as the epact. At the end of the second year the new moon falls 22 days sooner than in the first year. The epact of the third year is three, because if 11 be added to the 22, the result is 33, and from this 33 we subtract 30 days which make up a lunar embolism and the remainder gives us 3, the epact for the year, and so on.
In the Breviary there is a table (alia Tabella epactarum) corresponding to the golden numbers from the year 1901 to the year 2000 inclusive. To take away all doubt in the use of this table, a new table of epacts, an example may be quoted. In the year 1901 the epact was X, which is placed under the golden number 2; and new moons appear on the 21st January, 19th February, and 21st March…. Again, in 1911 the epact is not marked by a number, but by an asterisk (see Table in Breviary) which is placed under the golden number 12, and in the calendar for the whole year will indicate the new moon on January 1st, January 31st (for in February there is no new moon indicated in the Table; the sign [*] is not found), on March 1st, March 31st, and on April 29th. In the year 1916 the golden number is 17 and the epact is 25 (written not in Roman numerals but in ordinary figures), the new moons occur on 6th January, 4th February, 6th March, 4th April, etc. For when the epact is 25, corresponding with golden numbers greater than the number 11 in the calendar, we must take in computation the epact 25 (written in modern figures) but where the epact corresponds with numbers less than the number 11, in the tabella, the epact XXV. in Roman numerals must be taken in calendar countings. This change takes place with epact 25 only, so that the computation of the lunar years may more closely respond to the solar year. It is for this cause, too, that in six places in the calendar two epacts, XXV. and XXIV., are given.
The new Breviary contains a tabella of Dominical letters, up to the year 2000 A.D. It needs no comment.
Indiction. Indiction was a cycle of fifteen years, the first of which dated from the third year of the Christian era. It was usual to indicate the number of the year in a cycle and no mention was made of the cycles already completed. Thus, the indictio sexta meant the sixth year of a cycle and not the sixth cycle or period of fifteen years. Hence, to know the year of indiction is useless for determining the date in old documents of State. Indiction was instituted by Constantine in 313 for fiscal purposes. In papal and imperial documents the name of Pope or emperor was generally given and the regnal years noted.
Movable Feasts. In virtue of the decree of the Council of Nice, in 325, Easter, on which all other movable feasts depend, must be celebrated on the Sunday which follows immediately the fourteenth day of the moon of the first month (in the Hebrew year), our March. Easter, then, is the first Sunday after the Paschal full moon (i.e., the full moon which happens upon or next after March 21st). If full moon happens on a Sunday, Easter Sunday is the Sunday after the full moon. The matter of the arrangement of Easter was for long a subject of very bitter contention in the Irish and in the English Church. The Irish, clinging tenaciously to the calendar of St. Patrick, carried it everywhere in their missionary labours, so that the controversy was not confined to Ireland and England. It was long and bitter, until at last the Irish Church agreed to follow the reform. (See Healy, Ireland's Schools and Scholars, p. 592; Moran, Irish Saints in Great Britain, "The Conference at Whitby in 664," pp. 255-261).
Calendar study is interesting, and many valuable contributions on this matter have been given to us by Father Thurston, S.J., and other English and Irish scholars.