『세초유휘(細草類彙)』곤(坤)에 기록된 달 위치 추보 = CALCULATION OF MOON’S POSITION DESCRIBED IN SECHOYUHUI(細草類彙)

다국어 초록 (Multilingual Abstract)

We see that the method of calculating the moon's position in the celestial sphere is little different from the method currently used. Currently, an elliptical model is used, while Sechoyuhwi and Chongzhen Lishu(崇禎曆書) use a four-epicycles model descibed in Lixiang Kaocheng(曆象考成) when calculating the equations of the Moon. The equation of center(EoC) calculated in this way has little difference from the currently calculated EoC. Considering the four-cycles model, the EoC occurs due to the center difference of the moon's orbit. The evection and variation occur when the sun exerts gravitational perturbation on the moon's orbit, and those are expressed as the 2nd and 3rd equations. However, when calculating the moon's position, Sechoyuhwi and Chongzhen Lishu used the apparent solar time. therefore these almanacs deal with another equation which is not the same as the 4th equation described as the equation of annual inequality.
Furthermore these calendars consider the longitude reducing when the longitude along the lunar path in the celestial sphere is converted to that along the ecliptic. In this case the same as the 5th equation described as the equation of reduced ecliptic is corrected. When the ecliptic latitude were calculated, these calendars have considered the latitude evection of the lunar inclination to the ecliptic with the two-cycles model. At the time when Sechoyuhwi was written, Joseon’s lunar position tracking was at the highest level before Newton knew how to do it.

참고문헌 (Reference)

• 1 최승언, "Theoretical considerations on the movement of the sun covered in Joseon's Siheon Almanac-Focusing on Sechoyuhwi, Siheongiyo, and Chubosokhae" 12 : 137-149, 2021
• 2 Choe, S. -U., "The basics of the Siheon Calendar, the movement of the sun" 敎育科學社 2023
• 3 Huh, W., "Sechoyuhwi Gon"
• 4 Newton I., "New and most Accurate THEORY of the Moon’s Motion; written by Isaac Newton and published in Latin by David Gregory in his Excellent Astronomy London" A. Baldwin in Warwick-lane 1702
• 5 Korea Astronomy & Space Science Institute, "Calendar 2023"
• 6 Fitzpatrick, R., "A Modern Almagest"