LUNAR LETTER. - In medieval calendars, among other elements, the age of the moon was also indicated. In order to determine the beginning of the new moon, the Middle Ages resorted to the so-called system of l. l., analogous to that of ferial letters.
This system comprised 59 letters distributed in three groups: the first of 20 letters (from A to V, called litterae nudae), the second of 20 (from A to V, called litterae postpunctatae or subnotatae), and the third of 19 (from A to T, called litterae praepunctatae or supernotatae), by which the days of two consecutive lunations were indicated. By means of these letters it was possible to determine, besides the beginning of the new moons, also the age of the moon on each day of the year; in leap years the added day bore the same number as the preceding day. The l. l. sometimes entered into the dating of medieval documents to designate the year (littera annalis); in that case the indicated letter corresponded to the day of the March full moon (terminus paschalis). The system of l. l. fell into disuse in the 11th century.
Niccolò Del Re