Hwang Yoon-Seok was an 18th century expert on astronomy (tianwen) and calendrical science (lifa), actively involved in academic and social discussions with many contemporaries, including astronomers and calendrical scientists while living in Seoul. Hwang kept a diary where he wrote the details of those conversations, therefore providing a valuable primary source for the study of the 18th century astronomy and calendrical science. His diary, Yi-Jae-Ran-Go, contains his own views and experiences, the analysis of which would enlighten our understanding of the 18th century astronomy and calendrical science.
Hwang accepted the idea of the round Earth, supported the new law regarding the theory of precession, and embraced the theory for eclipse phenomena from the west. Even though he explained various natural phenomenon through the western knowledge, the direction of his natural science was not “modern”. He admitted the superiority of western mathematics and astronomy which were foundations of Shixian li (a calendar based on Western mathematical calculations), but also argued that their logic differed little with the sages of Confucianism. Also, Hwang’s interest in astronomy and calendrical science was in the realm of lüli zhi xue (study on harmonics and calendar) and lüli suanshu zhi xue (study on harmonics, calendar, and mathematics). In short, he tried to access Lüli yuanyuan from the perspective of lüli suanshu zhi xue, hoping to complete the studies of ancient sages and set up an authentic precedent of Joseon dynasty.
Amongst the critical problems astronomy and calendrical science of the late Joseon dynasty faced were the problem between the old law and the new law. This rivalry between the traditional astronomy and calendrical science and the Western astronomy and calendrical science was caused after the reception of Shixian li. The intellects of the late Joseon dynasty attempted to establish a new astronomy and calendrical science which could embrace both. Hwang stood out as one of those.