P2.015 — Analysis of the Lunar Eclipse Records from the Goryeosa

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Aug 10th at 6:00 PM until 6:00 PM

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Author(s): Ki-Won Lee1, Byeong-Hee Mihn2, Young Sook Ahn2, Sang-Hyeon Ahn2

Institution(s): 1. Catholic University of Daegu, 2. Korea Astronomy and Space Science Institute

We study the lunar eclipse accounts in the Goryeosa (History of the Goryeo Dynasty), an official history book of the Goryeo dynasty (A.D. 918 - 1392) of Korea, in order to verify the calendar dates of the dynasty. In the history book, a total of 228 lunar eclipse accounts are recorded, covering the period from 1009 to 1392. However, we find that two accounts are duplications and four accounts correspond to no known lunar eclipses. For the remaining lunar eclipses, we calculate the magnitude and the time of the eclipse at different phases using the DE406 ephemeris. Of the 222 lunar eclipse accounts, we found that the minimum penumbral magnitude was 0.5583. In addition, we found that for eclipses which occurred after midnight, some accounts were recorded on the day before the eclipse, while others were recorded on the day of the lunar eclipse; this is different from the astronomical records of the Joseonwangjosillok (Annals of the Joseon Dynasty). We also found that four accounts show a difference in the Julian dates between this study and that of Ahn et al., even though it is assumed that the Goryeo court did not change the dates in the accounts for lunar eclipses that occurred after midnight. With regard to the contents of the lunar eclipse accounts, we confirmed that the 20 accounts recorded as the total eclipse are true, except for two accounts. However, the two eclipses were very close to the actual total eclipse. We also confirmed that all predicted lunar eclipses did occur, although one eclipse happened two days after the predicted date. In conclusion, we believe that this study is very useful for verifying the calendar dates of the Goryeo dynasty, and furthermore, helpful for investigating the lunar eclipse accounts of other periods in Korea.