• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.137.2-137.2
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• 2011

규표(圭表)는 남중하는 해의 그림자를 측정해 일 년의 길이와 절기를 알아내기 위한 관측 기기이다. 규표에 대한 우리 역사 기록에 따르면 조선시대에 8척과 40척 크기의 규표를 만들어 사용한 것으로 알려져 있다. 세종대에 간의대 서쪽에 설치한 40척 규표에 대해서는 그 구조와 크기가 상세히 기록되어 있지만 8척 규표에 대해서는 명종대의 관측 사실만이 남아있을 뿐이다. 8척 규표에 관한 국내 외 문헌과 중국에 남아 있는 유물을 조사하여 조선의 8척 규표 모델을 새롭게 복원하였다. 복원한 8척 규표는 주척(周尺, 1척=20.7cm)을 기준으로 규 21척, 표 8척의 크기이다. 오석으로 만든 규면에는 16척 길이의 눈금을 1분(2.07cm) 단위로 새겨놓았다. 청동으로 만든 표의 꼭대기에는 그림자를 명확히 나타내기 위해 길이 2척, 지름 1.2cm의 횡량(橫樑)을 설치하였다. 또한 횡량의 그림자를 정확하게 측정하기 위해 규면에 설치할 영부(影符)도 함께 연구 복원하였다. 규면에 새겨진 못(池)과 물홈(水渠)의 모양은 한국과 중국의 천문유물에 남아 있는 여러 자료와 구조적 기능을 고려해 결정하였다. 지금까지 국내에서 복원된 규표는 8척 규표에 대한 문헌 자료가 부족했기 때문에 40척 규표의 구조를 축소해서 만들어왔다. 이번에 복원한 조선의 8척 규표는 40척 규표의 축소 모형이 아닌 새로운 모델을 연구하여 제작한 것으로 한국천문연구원 앞뜰 간의 서편에 설치하였다.

• Journal for History of Mathematics
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• v.25 no.4
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• pp.83-99
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• 2012

The conic sections are defined as algebraic expressions using the focus and the directrix in the high school curriculum. However it is difficult that students understand the conic sections without environment which they can manipulate the conic sections. To make up for this weak point, we have found the evidence for generating method of a conic section through a sundial and investigated the history of terms 'focus', 'directrix' and the tool of drawing them continuously.

• Publications of The Korean Astronomical Society
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• v.26 no.3
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• pp.115-127
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• 2011

Since the thirteenth century, large scale facilities and various instruments for astronomical observation were built and installed in East Asia. During the Yuan Dynasty, S. ti.ntai (Beijing astronomical observatory in the Yuan Dynasty, 司天臺) was built in Beijing in 1279. Various astronomical instruments, including Ganui (Jianyi, simplified armillary sphere, 簡儀), Yang-yi (upward hemisphere, 仰儀) and Gyupyo (gnomon, 圭表) were installed in this observatory. These astronomical instruments were modified and improved by researchers of the Joseon Dynasty. Ganuidae (Joseon astronomical observatory, 簡儀臺) was built in Gyeongbokgung (or Gyeongbok palace, 景福宮), Seoul. Its scale was 31 Cheok (Korean feet in the Joseon Dynasty, 尺) in height, 47 Cheok in length and 32 Cheok in width. Lee, Cheon (李蕆, 1376~1451), a responsible leader of Ganuidae project, set up various astronomical instruments with his colleagues. Ganui and Jeongbangan (direction-determining board, 正方案) were installed at the top of this observatory. Gyupyo was installed at the west side of this observatory and Honui (armillary sphere, 渾儀) and Honsang (celestial globe, 渾象) were installed in a small pavilion which was located next to Gyupyo. A decade after installation, this observatory was moved to the north-west side of the palace but almost destroyed during Japanese invasion of Korea in 1592 except Ganuidae. We have analyzed documents about Ganuidae and investigated Chinese remains of astronomical observatories and artifacts of astronomical instruments. In this paper, we suggest the appearance, structure, arrangement and scale of Ganuidae, which are expected to be used for the restoration of Ganuidae at some day in the near future.

• Publications of The Korean Astronomical Society
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• v.33 no.2
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• pp.9-19
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• 2018

We investigate the life of Lee Cheon (1376-1451) who was closely connected with astronomy during the reign of King Sejong of the Joseon dynasty. Lee Cheon is widely regarded as one of the outstanding scientists of King Sejong's period. However, his contributions to the development of the astronomy during the period have not been enlightened. Based on the historical records on the life and achievements of Lee Cheon, mainly referring to the Joseonwangjosillok (Annals of the Joseon Dynasty), we address three important points. First, Lee Cheon was a distinguished administrator who filled various government posts. Second, he was a supervising engineer in public works and metal smelting during his position in military. Third, he was a scientific technician and manufactured precision equipment such as the metal movable type sets. By virtue of these aspects, Lee Cheon was taken into confidence by King Sejong on the Ganui-dae project (i.e., manufacture various astronomical instruments and construct their platform in order to make a calendar suitable for Joseon). During the period of this project, Lee Cheon not only supervised the construction of the Ganui (simplified armillary sphere) and Ganui-dae (platform for astronomical instruments) but also participated in the production of the astronomical instruments such as Gyupyo (Gnomon) and Honcheonui (Armillary Sphere). In conclusion, we regard Lee Cheon as one of the astronomers who led a great advance in astronomy during King Sejong's era.

• Journal for History of Mathematics
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• v.21 no.4
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• pp.153-168
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• 2008

This study investigates how high achievers solve a given mathematical problem. The problem, which comes from 'SanHakIbMun', a Korean mathematics book from eighteenth century, is not used in regular courses of study. It requires students to determine the area of a gnomon given four dimensions(4,14,4,22). The subjects are 84 sixth grade elementary school students who, at the recommendation of his/her school principal, participated in the mathematics competition held by J university. The methods used by these students can be classified into two approaches: numerical and decomposing-reconstructing, which are subdivided into three and six methods respectively. Of special note are a method which assumes algebraic feature, and some methods which appear in the history of eastern mathematics. Based on the result, we may observe a great variance in methods used, despite the fact that nearly half of the subject group used the numerical approach.