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6.2.3.1.2.1.2
dominical_letter () |
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The dominical letter identifies the type of year. A year that begins on Sunday has the letter A. There are seven letters, A through G, one for each day of the week. In common years, this information suffices completely to describe the structure of the year. |
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In leap years, two letters are used. The first identifies the structure of the months of January and February, and the second letter describes the remainder of the year. |
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Medieval calculations of Easter involved tabulations of these letters. The term leap year is derived from the fact that the ordinary progression of letters is interrupted in leap years, when the sequence "leaps" over a letter. |
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The use of letters derives from the earlier Roman usage of the letters A through H to denote the eight days of the Roman nundina. The letter H was dropped as the Jewish seven-day week was gradually adopted throughout the Roman empire. |
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The dominical letter is still used by the Roman Catholic Church to regulate certain ceremonies (Listing 6.8). |
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| Listing 6.8 dominical_letter () | |
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/* dom_ltr.c
+-------------------------------------------+
| Copyright (C) 1995 by Lance W. Latham. |
| All rights reserved. |
+-------------------------------------------+
Returns the single dominical letter (for common years) or the two dominical
letters (for leap years) for any year in the Julian or Gregorian calendar.
INPUTS:
1. year, type int, the year (A.D.) in the Western calendar for which
the dominical letter is desired.
OUTPUTS:
1. returned by routine, string containing the one or two dominical
letters for the input year.
Condition Routine returns
--------- ---------------
Error NULL
Common year 2-character string. First character is the single
dominical letter for the year.
Leap year 2-character string. First character is the dominical
letter for JanuaryFebruary. Second character is the
dominical letter for the remainder of the year.
NOTES:
1. Each common year is associated in the ecclesiastical calendar with a
letter of the alphabet, 'A' through 'G', which defines the set of dates
on which Sunday occurs. E.g., the letter 'A' (returned as string "A ")
denotes a year in which the Sundays occur on:
1, 8, 15, 22, 29 January
5, 12, 19, 26 February
5, 12, 19, 26 March
and so on.
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