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This section describes the structure of the GLC and provides some historical material as background. |
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9.12.5.2.1
Structural Details |
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The GLC is a completely lunar calendar intended to take little notice of the sun. The year consists of 25 lunar months, numbered 1 through 25. Odd-numbered months contain 30 days; even-numbered months have 29 days. The year, therefore, is a calendric year, and not related to the solar year in any direct sense. |
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As a notational matter, each month in the GLC is named after a goddess from one of 14 different cultural traditions. The names are chosen in alphabetical order, so that the first month, Artemis, begins with the letter A, and each month name begins with a succeeding letter, A through Y. |
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Years in the GLC are numbered. A leap year rule exists for the GLC, which states that years whose numbers are evenly divisible by four or 51 are leap years. In a leap year, the 24th month has one epagomenal day, and so contains 30 days, not 29. The year numbering uses the astronomical convention that zero is a counting number. |
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The purpose of the intercalation is not the adjustment of the calendar to the length of the solar year. Rather, the calendar and its leap year rule are intended to match the average synodic lunar period closely. |
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The structure of the GLC, owing to the leap year rule, repeats every (451 =) 204 calendric years. In this period, there are (20425 =) 5,100 lunar months. The total number of days in this period can be computed in the following fashion: |
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The number of days in a common calendric year is (1330 + 1229 =) 738 days. |
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The number of days in a leap year is one more, or 739 days. |
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The number of leap years in 204 calendric years is calculated by noting that a leap year occurs by division by four a total of 51 times, and by division by 51 a total of four times. The number 204 is evenly divisible by both 4 and 51, so only one occurrence of division is counted. There are therefore (51 + 4 1 =) 54 leap years in 204 calendric years. |
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Therefore, there are (204 54 =) 150 common years in the period. |
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Therefore, there are (150738 + 54739 =) 150,606 days in the 204-year period or 150,606 days in 5,100 lunar months. |
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Hence, the calendar predicts an average lunar month length of (150,606 days/5,100 lunar months =) 29.530588 days, which is, to six decimals, the accepted value for the synodic lunar period (SLP). |
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The average length of the calendric year is therefore (150,606/204 =) 738.2647 days, or slightly more than 2.02 tropical solar years. |
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