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.

ABSTRACT
1. 서론
2. 수학적 해설
    2.1. 월리(月離)를 계산하는 방법(推月離細草)
    2.2. 합삭과 현, 망 시각의 계산
    2.3. 태음의 교궁을 계산하는 방법
    2.4. 월승을 구하는 법
    2.5. 월리의 연근을 구하는 법
    2.6. 월패·나후·계도의 입수를 구하는 법
3. 『세초유휘』월리 추보의 현대적 이해
    3.1. 천체의 궤도 구하기
    3.2. 달의 황도 좌표 구하기
    3.3 『세초유휘』에서 달의 황도좌표 구하는 방법과의비교
4. 나가면서
ACKNOWLEDGMENT
REFERENCES
APPENDIX
    A1. 『숭정역서』〈윌리표〉에서 차균을 구하는 방법
    A2. 4륜(輪)모델
    A3. 4륜(輪)모델 시뮬레이션
    A4. 『세초유휘』 달 관련 주요 원문번역
        A4.1. 월리(月離)를 계산하는 방법(推月離細草)
        A4.2. 합삭과 현, 망 시각의 계산
        A4.3. 태음의 교궁을 계산하는 방법
        A4.4. 월승을 구하는 법
        A4.5. 월리의 연근을 구하는 법
        A4.6. 월패·나후·계도의 입수를 구하는 법

• 최승언(서울대학교) | SEUNG-URN CHOE (Seoul National University, Seoul 08826, Korea)