Calendar Differences in the Three Kingdoms Period (223 – 280)

In 237, emperor Mingdi of the Wei dynasty declared that the chǒu month (present day month 12) would be the first month of a year; the yín month (present day month 1) became month 2 and so on. The Chinese month numbers were shifted by one. The new system was imposed after month 2 in the Chinese year in 237, in which month 4 was followed by month 2. When the emperor died in 239 CE., the month numbers were switched back with month 1 being the yín month again in the following year. As a result, the Chinese year in 239 had 13 months, where month 12 appeared twice. To prevent confusion, the month order is not changed here. Month 1 still refers to the yín month in 237-239. In addition, in the book 3500 Years of Calendars and Astronomical Phenomena, the main text uses a new calendar (based on the Jǐngchū astronomical system) beginning in month 1 in 237, but Appendix 2 of the book starts using the new calendar in month 5 in 237. Here I follow the main text and start using the new calendar in month 1 in 237. The conjunction days before month 5 were one day earlier than the old calendar (the same one used by the Shu dynasty).

In Appendix 2 of the book 3500 Years of Calendars and Astronomical Phenomena, the sexagenary day of the leap month conjunction in the Wu state is listed as jǐ chǒu, corresponding to Nov. 25. This is at odds with my calculation. The result of my calculation is consistent with the data on the Chinese-Western calendar conversion website created by Academia Sinica in Taiwan. The preface of the book says that the calendar data in its appendices are based on the book 《歷代長術輯要》(Compilation of Historical Calendars) by Wāng Yuēzhēn (汪曰楨). I looked at the book and found that the date listed there was also the same as my calculation. I suspect that the date listed in 3500 Years of Calendars and Astronomical Phenomena is wrong. The book also lists the sexagenary day of the month 11 conjunction in the Wu state as jǐ chǒu, which is certainly wrong since this date was far away from the new moon close to the beginning of month 11.