Dominical letter
After the introduction of Christianity a similar sequence of seven letters A–G was added alongside, again commencing with January 1.
[4][5] After the 1662 reform there was correspondence between the Archbishop of Canterbury and the printer of the Book of Common Prayer, in which it was explained that the feast day of St Matthias now fell on February 24 every year.
According to Thurston 1909, p. 109 dominical letters are:a device adopted from the Romans by the old chronologers to aid them in finding the day of the week corresponding to any given date, and indirectly to facilitate the adjustment of the 'Proprium de Tempore' to the 'Proprium Sanctorum' when constructing the ecclesiastical calendar for any year.
The Church, on account of her complicated system of movable and immovable feasts... has from an early period taken upon herself as a special charge to regulate the measurement of time.
To secure uniformity in the observance of feasts and fasts, she began, even in the patristic age, to supply a computus, or system of reckoning, by which the relation of the solar and lunar years might be accommodated and the celebration of Easter determined.
Naturally she adopted the astronomical methods then available, and these methods and the terminology belonging to them having become traditional, are perpetuated in a measure to this day, even after the reform of the calendar, in the prolegomena to the Breviary and Missal.The Romans were accustomed to divide the year into nundinæ, periods of eight days; and in their marble fasti, or calendars, of which numerous specimens remain, they used the first eight letters of the alphabet [A to H] to mark the days of which each period was composed.
Continuing in this way, 30 January was marked with a B, 31 January with a C, and 1 February with a D. Supposing this to be carried on through all the days of an ordinary year (i.e. not a leap year), it will be found that a D corresponds to 1 March, G to 1 April, B to 1 May, E to 1 June, G to 1 July, C to 1 August, F to 1 September, A to 1 October, D to 1 November, and F to 1 December – a result which Durandus recalled by the following distich: Alta Domat Dominus, Gratis Beat Equa Gerentes
Contemnit Fictos, Augebit Dona Fideli.Another one is "Add G, beg C, fad F," and yet another is "At Dover dwell George Brown, Esquire; Good Christopher Finch; and David Fryer."
The 23rd is ante diem vii kalendas Martias, the next day in a leap year is a.d. bis sextum kal.
The relevant line of the Februarius page in the Kalendarium of a 1913 Breviarium Romanum reads: The first column is the epact, a replacement for the golden number, from which the age of the moon was computed and announced in some English cathedrals prior to the Reformation.
A note at the foot of the page reads: In anno bissextili mensis Februarius est dierum 29. et Festum S. Mathiae celebratur die 25.
Februarii et bis dicitur sexto Kalendas, id est die 24. et die 25. et littera Dominicalis, quae assumpta fuit in mense Januario, mutatur in praecedentem; ut si in Januario littera Dominicalis fuerit A, mutatur in praecedentem, quae est g.
(In a bissextile year the month February is of 29 days and the Feast of St. Matthias is celebrated on 25 February, and twice is said on the sixth Kalends, that is on the 24th and 25th, and the Sunday letter, which was assumed in the month of January, is changed to the preceding; so if in January the Sunday letter may have been A, it is changed to the preceding, which is G.
Of the 28 years in one Julian cycle, there are: The dominical letter of a year can be calculated based on any method for calculating the day of the week, with letters in reverse order compared to numbers indicating the day of the week.
[6] The procedure accumulates a running total T as follows: The formula is This rule was stated by Augustus De Morgan: So the formulae (using the floor function) for the Gregorian calendar is It is equivalent to and For example, to find the Dominical Letter of the year 1913: De Morgan's rules no.
In the case of the Revised Julian calendar, find the date of Easter Sunday (see the section "Calculating Easter Sunday", subsection "Revised Julian calendar" below) and enter it into the "Table of letters for the days of the year" below.
Note the different rules for leap years: When a country switched to the Gregorian calendar, there could be some unusual combinations of dominical letters.
The duration of months, and the number and placement of intercalated days also changed inconsistently before AD 42 in the early local Julian calendars which used native names for the months, depending on places and years, causing finally a lot of confusion in the population (so dating events precisely in that period is often difficult, unless they are correlated with observed lunar cycles, or with days of the week, or with another calendar).
As well, all these early years were effectively counted inclusively and positively from a different, much earlier epoch in other eras, such as the supposed foundation of Rome, or the accession to power of a local ruler (and still not relatively to the supposed date of birth of Christ, which was fixed later arbitrarily by a Christian reform for the modern Julian calendar so that this epoch for the Christian era starts now on January 1 in proleptic year AD 1 of the modern Julian calendar, but the real date of birth of Christ is still not known precisely but certainly falls before, somewhere in the last few BC years).
Enter the table with the Julian year, and just before the final division add 50 and subtract the quotient noted above.
The Pye or Directorium which preceded the present Ordo took advantage of this principle by delineating all 35 possible calendars and denoting them by the formula "primum A", "secundum A", "tertium A", et cetera.
Hence, based on the dominical letter of the year and the epact, the Pye identified the correct calendar to use.
A similar table, adapted to the reformed calendar and in more convenient form, is included in the beginning of every breviary and missal under the heading "Tabula Paschalis nova reformata".
Saint Bede does not seem to have been familiar with dominical letters, given his "De temporum ratione"; in its place he adopted a similar device of Greek origin consisting of seven numbers, which he denominated "concurrentes" (De Temp.
The "concurrents" are numbers that denote the days of the week on which March 24 occurs in the successive years of the solar cycle, 1 denoting Sunday, 2 (feria secunda) for Monday, 3 for Tuesday, et cetera; these correspond to dominical letters F, E, D, C, B, A, and G, respectively.
