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Islamic calendar, it is not schematic or rule based. Because lunar motion is so complex, the algorithms for predicting lunar position have a useful limit of about 100 years on either side of a known epoch for which the position is established by observation. This fact has its own consequences: |
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1.1.) Any algorithm that converts arbitrary Chinese dates to Julian Day numbers is either complex, if calculational, or tediously slow, if record based. |
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1.2.) Knowledge of future Chinese dates requires calculation. Therefore, future dates are difficult to predict accurately beyond a horizon of about 100 years. |
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1.3.) Knowledge of past Chinese dates requires either calculation or records. If records are available, they must be complete and accurate. |
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2.) There is no single the Chinese calendar. China is the oldest continuous culture on the planet. Between the fourth century B.C. and the 18th century A.D., over 100 calendars and changes have been identified. The rules for defining New Year changed several times, historically. |
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3.) The Chinese have been a literate society for a very long time. This fact has the disadvantage that the Chinese have therefore also been editing, summarizing, distorting, and censoring their records for a very long time. |
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4.) The Chinese never, until the 20th century, used a single era for the purposes of dating in a linear fashion. Rather, they dated years by a complex regnal system. Without complete and accurate records, determining the historical context of such a date is difficult or impossible. With such records, it is merely excruciatingly tedious. |
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5.) For many periods in their history, the Chinese were not a unified country. There were, therefore, many competing states and many different regnal dating systems in simultaneous operation. Converting a given date to a Julian Day number may be difficult, but the reverse operation presents a quandary, since it is a one-to-many problem. |
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6.) Observations and the entire reference frame for calendric matters is alien to Western astronomical traditions. |
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Fortunately, all of these problems have solutions of one sort and to one or another: |
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The Chinese kept meticulous and thorough records. The Chinese have also been blessed with bureaucratic government longer than any other culture. Using the records, it is possible to determine past new moon dates and therefore, years and months, for many centuries. |
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The many-to-one problem can be solved by using the concept of the Principal Dynasty. At any given time, one dynasty is considered as constituting a sequential part of a continuous thread of legitimate imperial authority. |
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The sole serious problem remaining for the Chinese calendar is the fact that future dates are difficult or impossible to predict. One must simply accept a certain horizon for future dates as a kind of ineluctable epistemological limit. |
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