Literally, the "Sunday" letter. To connect a week day with a day of the year, January 1 is A; 2, B; 3, C; 4, D; 5, E; 6, F; 7, G. Thus 8 becomes A, and so on. However, if one says that the Dominical letter is C then January 1 of that year will fall upon Friday. Its chief use is in connection with an involved system for determining the date upon which will fall the "movable feast" known as Easter, around which the Ecclesiastical calendar is arranged. The letters of successive years rotate in the reverse order: on Leap year the preceding letter applies only to January and February dates, the next preceding letter applying to the remainder of the year. For example, 1929, F; 1930, E; 1931, D; 1932, January-February, C; March-December, B; 1933, A; 1934, G; and so on.
ASTROLABE ENCYCLOPEDIA
