The letter used in liturgical calendars to denote the Sundays in a particular year. Since to determine the date of Easter one must know the sequence of the days of the week following the paschal full moon, the early Christians devised special tables, basing these on existing Greco-Roman computations of the seven possible relationships of the days of the week to the calendar of the year. Thus, in the time of Augustus the Romans had allotted the letters A to G of the alphabet to the seven days of any of the 52 seven-day cycles of the full year, beginning from January 1. In Christian usage, therefore, the Dominical or Sunday letter for any given year is the letter that occurs on the first Sunday of the first cycle; and in a normal year the date of all the other Sundays will follow automatically, as the Dominical letter recurs in each of the 52 cycles. In the sequence of years, however, the Dominical letters run in a retrograde series (G-A), since a year that begins, for example, on a Monday (yielding on Sunday, January 7, the Dominical letter G) is commonly succeeded by a year beginning on a Tuesday (giving the Dominical letter F on January 6). Thus, since Jan. 1, 1962, fell on a Monday and the first Sunday of 1962 on January 7, the Dominical letter for 1962 was the seventh letter, i.e., G. In 1963, however, January 1 was on a Tuesday, so the first Sunday fell on January 6, and the Dominical letter for 1963 was therefore F. Again, Jan. 1, 1965, was on a Friday, so the first Sunday was on the third day of 1965, giving C as the Dominical letter for that year. The year 1964, however, is more complicated since it is a leap year. In a leap year (annus bissextilis ) there is an extra day in February, and this was denominated dies bissextus from the fact that VI Kal. Mar. (February 24) was the day selected for doubling (in the modern system the extra day is added after February 28). The insertion of this doubled day in February means that there is a change in the seven-day cycle of letters at this point, so that the Dominical letter for the period after the extra day (February 24 or 28) must differ from that governing the Sundays from January 1.
The Dominical letter does not seem to have been familiar to bede in his De temporum ratione (c. 725), but in its place he adopts a similar device of Greek origin that uses seven numbers (1–7), called concurrentes by Bede; these denote the day of the week on which March 24 falls in the successive years of the solar cycle, one standing for Sunday, two for Monday (feria secunda ), three for Tuesday (feria tertia ), etc. A table coordinating the Dominical letter with concurrentes and other reckonings of the year is conveniently included at the beginning of every breviary and missal under the heading Tabula paschalis nova reformata.
Bibliography: bede, Patrologia Latina: De ratione temporum, ed. j. p. migne, (Paris 1878–90) 90. g. durandus, Rationale divinorum officiorum (Lyons 1560, Venice 1568). c. clavius, Romani calendarii a Gregorio XIII restituti explicatio (Rome 1603). j. lacau and p. calot, Dictionnaire de droit canonique, ed. r. naz (Paris 1935–65) 2:1243–46. c. r. cheney, A Handbook of Dates for Students of English History (London 1945).
[l. e. boyle/eds.]