Of the various sets of Irish annals, the two that have most relevance to this website are the ‘ANNALS OF TIGERNACH’ and the ‘ANNALS OF ULSTER’.
The ‘Annals of Tigernach’ is the name given to the remnants of a compilation, written in a mixture of Latin and Early Modern Irish, the important parts of which – three fragments, covering the periods 488–766, 974–1003 and 1018–1178 – are preserved in a 14th century manuscript (Oxford, Bodleian MS Rawlinson B 488). The annals are named from Tigernach hua Braein, abbot of Clonmacnoise, who is traditionally credited with compiling the work down to his death in 1088. This attribution is, however, now thought to be groundless, but the name, being well established, remains.
The earliest fragment of the ‘Annals of Tigernach’ mentioned above, dated 488–766, shares a common ancestor text with the ‘Annals of Ulster’. Actually, the dates given to the fragments are inferred – the ‘Annals of Tigernach’ does not use Anno Domini dating. The beginning of each new annal is indicated by K. or Kl., standing for the Kalends (i.e. the first day) of January. In some sections, though, a ‘ferial number’ is added to indicate the day of the week that the Kalends of January fell in that year. For instance, Kl. iii. means that 1st January was on a Tuesday (third day of the week) that year. This circumstance will not occur again for twenty-eight years. Additionally, from 1019 onwards the moon's age on 1st January (the ‘epact’) is also noted. However, the system is fragile – leap years must be correctly incorporated into the count, and, generally, Roman numerals are susceptible to scribal error – and for annals falling after 655 and before 1019 there is no ferial data at all. Dating entries in the ‘Annals of Tigernach’ is generally achieved by comparing them with entries in the ‘Annals of Ulster’, which do have A.D. references.
The ‘Annals of Ulster’ cover the period from 431 until 1540. Compilation began in the late-15th century, under the direction of one Cathal Óg Mac Maghnusa (who died of smallpox in 1498), and up to 1489 it was the work of a single scribe: Ruaidhri Ó Luinín. This original manuscript survives (Dublin, Trinity College MS 1282), though with a number of missing sections. Some of these gaps can be filled from a 16th century copy (Oxford, Bodleian MS Rawlinson B 489). The entries are written in a mixture of Latin and Irish, and the development of the Irish language – from Old, through Middle, to Early Modern – is evident.
There is a well known difficulty with the A.D. sequence presented by the ‘Annals of Ulster’. Marjorie O. Anderson explains:
“... something must be said about the A.D. year-numbers in AU [‘Annals of Ulster’], which afford the usual and the only convenient method of reference. They are written in the original hand, but were certainly introduced into the text no earlier than the tenth century. The first item, the mission of Palladius to Ireland, is dated “A.D. 431”, which is the true year to be inferred from Prosper's chronicle; and thereafter AU's numbering is continuous. But the year sections down to the actual year 1013 are one too few. Assuming that the fault was not original, a year-section must have been lost by a copyist, perhaps somewhere in the 480s, certainly at some point before the end of the seventh century, since from about 700 onwards the addition of one to AU's year-number usually gives the true historical date, in those cases where it can be checked.”
‘Kings and Kingship in Early Scotland’ (1980) Chapter 1
In the translation used on this website (by S. Mac Airt & G. Mac Niocaill, 1983) annals from 488 until 1013 are accordingly incremented by one year (which does not, of course, ensure the historical accuracy of the date).
In two papers – ‘The Chronological Apparatus of the Annals of Ulster AD 431–1131’ (‘Peritia’, Vol. 8, 1994) and ‘The Chronology of the Irish Annals’ (‘Proceedings of the Royal Irish Academy’, Vol. 98C, 1998) – Daniel P. McCarthy argues that the A.D. chronology of the ‘Annals of Ulster’ was introduced in the early-11th century, and from the first annal up to 1012 the convention of beginning the year on the feast of the Annunciation (25th March following the 1st January when the year is now said to start) is followed, which, for the modern reader, has the effect of attributing an annal to the year before that which was intended. Dr McCarthy contends that the record of Palladius' mission would have been placed in 432, had an error in the kalend count of his source material not led to the compiler to place the entry in 431, which, by accident, is the correct date using a 1st January year beginning. After analyzing the contents of several sets of Irish annals, Dr McCarthy (who is in the Department of Computer Science at Trinity College, Dublin) has produced look-up tables (available on a website) in which the entries of these sets are displayed in synchronism on an A.D. framework.