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countdown of the waning moon. The last day was either the 29th or 30th in such schemes, and the actual value was often not known in advance. Clear evidence for such a system is seen in the Greek names for days of the month. The old Roman habit of numbering days of the month by counting down from several points within the month probably reflects a survival of the same scheme. |
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Third, because the length of the tropical year divided by the length of the average synodic lunar period is not an integer, any calendar that attempts to reconcile lunations and years will be rather complex. The Jewish calendar is a good example. |
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Fourth, the value of the quantity 365.2422/29.5306 = 12.368267 is the source for the importance of the number 12 in calendric matters, and later by extension, the origin of many numerologic and religious associations of the number. The 12 months completing the year became "secretly" associated with the concept of completion in general. The origins of triskaidekaphobia also may be traced to the awkwardness of the occasional 13-month year and the necessity of intercalating an extra month. |
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The week is not an astronomical unit, and it is not used at all by some calendars. When a week is used as a unit intermediate between day and month, it does not necessarily have seven days. Weeks of five, six, eight, or 10 days have also been used to subdivide months. |
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As it is used within the Gregorian calendar, the week is a somewhat arbitrary unit, mostly religious in origin, which was transmitted to the Western calendar from Babylonia via Jewish influence. |
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The most likely origin of the seven-day week goes like this: Babylonian astronomy and religion recognized the importance of the seven visible planets as visible deities and related these gods in a complex of beliefs and rituals to numbers, colors, directions, and so on in the characteristically all-encompassing way that ancient religions needed to relate all aspects of their cosmology. |
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This system included the belief that the seventh, 14th, 19th, 21st, and 28th days of a month were unlucky. Note that the number 19 is not anomalous in this series. In a 30-day month, the 19th day is the 49th (77 = 30 + 19 = 49) day counting from the prior month. This division of the month into roughly four parts probably originally corresponded to lunar phases. |
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The Jews, for their part, repeatedly were exposed to this set of ideas. The Lewy and Lewy paper ("The Origin of the Week and the Oldest West Asiatic Calendar," Hebrew Union College Annual, volume 17, pp. 1154, 19421943) outlines the essential argument for accepting the idea that the Jews used an early pentecontad calendar, derived from the Amorites, organized as seven periods of 50 days plus two additional seven-day periods making a total of [7(77 + 1) + 7 + 7 =] 364 days. Much was made of the number seven in this scheme, and it is undoubtedly the progenitor of the concept of the "Jobel" or "Jubilee," which occurs every fifty (77 + 1) years. The |
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