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2.7.2.1.) Lunar events. Easter is the best example. The rule of Victorius uses an artificial moon moving at uniform speed to calculate Easter date. |
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2.7.2.2.) Solar events. New Year's Day is an excellent example. The Gregorian calendar is an attempt to calculate the actual length of the solar year. The periodic designation of 1 January is, in effect, our statement of this calculated duration. |
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2.7.2.3.) Other astronomical. The Maya calendar again supplies examples. The Dresden Codex makes it highly likely that the Maya calculated the motion of Venus. In the Western calendar, various dates have been calculated for astrological purposes using rules of this sort. |
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2.8.) Feasts defined as being of a certain class, but depending upon a birthday. The "monarch's birthday" is an example. The rule remains the same, but the actual date changes with the monarch. |
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2.9.) Feasts defined as immovable in another calendar system not completely synchronized with the Western calendar. A person wanting to know the civil date for celebrating a Jewish birthday, for example, must first determine the date within the Jewish calendar (not necessarily a straight-forward procedure) and then determine the corresponding day in the civil calendar. |
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2.10.) Strictly cyclic. Sunday is a day of observance defined as occurring every seven days in a continuous cycle that ignores all other units. All of the days of the week are so defined. Other calendars have used other values for a week length, such as five (Soviet), eight (Roman Republican), and 10 (French Revolutionary). |
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2.11.) Hybrids. This section is the mixed bag of rules that do not otherwise fit the classification scheme. |
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2.11.1.) An immovable feast, unless it falls on a particular DOW. All Soul's Day is defined this way. |
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2.11.2.) Multiple days in one year, using different rules. This case is somewhat similar to that described in 1.1.1 above, but allows for rules other than fixed dates. The celebration of the Miracle of Saint Gennaro in Naples, for example, is defined as occurring on the first Saturday in May AND on 19 September. In this case, the same feast is defined as occurring at two different times of the year, and two different rules are used for the definitions. One rule defines a movable feast, and the other defines an immovable feast. |
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2.11.3.) Events that depend upon some natural phenomenon. In Cambodia, the lake Tonle Sap is connected to the Mekong River by the Tonle Sap River, which normally flows south from the lake. In the rainy season, the Mekong backs up and flows backward into the lake. Normal southward flow resumes when the dry season starts, and at this point the Festival of the Reversing Current is held. Such events, even though they occur annually, depend upon observation and cannot be predicted by date or rule. |
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