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2.4.2.1.) The movable feast is defined by its DOW. In this case, the resultant date can be determined by adding or subtracting a fixed number of days from the date of the movable feast. |
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2.4.2.2.) The movable feast is not defined by its DOW. If the movable feast does not always fall on a specific DOW, then the simple addition/subtraction scheme fails, and the DOW of the base date must be determined. An example might be the first Monday after Chinese New Year. |
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2.5.) The DOW closest to a date. The best known liturgical example is Advent Sunday, defined as "the Sunday of, or nearest to, Saint Andrew's Day". Saint Andrew's Day occurs on a fixed date, 30 November. |
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2.6.) The date N days before or after some other base date. An example would be the day 40 days before Easter. A good many of the days of the Easter cycle are defined by this rule. There are two cases: |
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2.6.1.) The base date is an immovable feast. This rule usually collapses to the fixed-date rule, unless an intercalary day can intervene. Epiphany can be defined by this rule (12 days after Christmas). |
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2.6.2.) The base date is a movable feast. There are two further subdivisions of this case: |
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2.6.2.1.) The movable feast is defined in terms of its DOW. This rule covers most of the days of the Easter cycle. Good Friday, for example, is defined as the Friday before Easter Sunday. |
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2.6.2.2.) The movable feast is not defined in terms of its DOW. This situation describes cases such as the day three days after the first new moon in July. In early times, lunar calendars based upon actual lunar phases made extensive use of this sort of rule. |
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2.7.) Dates specifically tied to astronomical events. There are two general cases: |
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2.7.1.) Dates tied to actual astronomical events. There are three cases: |
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2.7.1.1.) Lunar events. Chinese New Year is a good example. The Western calendar is explicitly a solar calendar, so it does not define events in lunar terms. |
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2.7.1.2.) Solar events. Examples include the summer and winter solstices and the vernal and autumnal equinoces. |
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2.7.1.3.) Other astronomical. There is accumulating evidence that certain Maya states coordinated their attacks on neighboring city-states with the helical rising of Venus, in an early variant of this rule that has been dubbed "Star Wars". No current practical example exists for the Western calendar. |
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2.7.2.) Dates tied to calculated or averaged astronomical events. Again, there are three types: |
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