• Journal of the Korean Society of Earth Science Education
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• v.5 no.2
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• pp.139-147
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• 2012

The purpose of this study was to explain how extraordinary the scientific technology or our ancestor was from the modern perspective by remodeling the most unique astronomical instrument, So-ganui (小簡儀), developed in the Sejong Period (世宗時代) after being examined with contemporary and the principles of the science and observational technology would be properly understood and measured directly. When measuring the altitude of the sun and azimuth using So-ganui, it was adjusted with the horizontal coordinate system and measured using Jipyeonghwan (地平環), Ipeunhwan (立運環) and Guyhyeong (窺衡). Based such measuring principles, the measurement accuracy proposed using So-ganui are as follows. The remodeled So-ganui produced approximately ${\pm}0.29$ degrees error on average at high altitude while in measuring the azimuth degrees, there was difference of ${\pm}0.35$ degrees. Since the theoretically, the measurement error for So-ganui was ${\pm}0.5$ degrees, the remodeled So-ganui could accurately measure at the high altitude compared to So-ganui from the Sejong period. In the study, So-ganui, which has disappeared, has been remodeled in modern perspective to be used as the educational material to accurately understand the principles of science and measurement technology from the Sejong period. The findings could contribute to raising the reputation in the astronomical observations from the documents from the Sejong period. Furthermore, this study has materialized the celestial and sky our ancestors have viewed with the observational principles of their times, on the computer screen via a webcam, bringing out interest in the traditional science for the students.

• Journal of the Korean Society of Earth Science Education
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• v.5 no.1
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• pp.1-7
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• 2012

The purpose of this study was to restore So-ganui(小簡儀), which is a unique astronomical instrument during Sejong period, so that its educational application can be sought. To achieve it, researcher researched the observation principle of our ancestors and the structure of So-ganui, and then restored So-ganui. The result is as following. First, So-ganui is the astronomical observation instrument which can not only measure the position of the celestial bodies in terms of function but also find out the height and distance of topography, and get the time. Second, restoration So-ganui is suitable for the students to learn as an inquiry activity of the observation information in the science curriculum and it would be used as the learning materials for the proper understanding of the science and measurement principle of our ancestors. This study would contribute to raising the level of pride in our scientific culture for the students and succeed the heritage of the science and culture.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.299-305
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• 2013

Ganui-Dae, built in the reign of King Sejong, Joseon Dynasty, is a comprehensive observatory. It has various instruments for observation and time signal such as Ganui, Gyupyo(Gnomon), water-hammering type Honui and Honsang, and so on. Studying on Ganui-Dae has been focused on its location, history, criterion, etc, so far. However, studying on its external form and construction method has been conducted insufficiently. This study suggests the model for restoration of Ganui-Dae. The model is based on the analysis about external form of Ganui-Dae in various antique maps, and its construction method in those days.

• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.231-242
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• 2002

So-ganui, namely small simplified armillary sphere, was invented as an astronomical instrument by Lee Cheon, Jeong Cho, Jung In-Ji under 16 years’ rule of King Sejong. We collect records and observed data on So-ganui. It is designed to measure position of celestial sphere and to determine time. It also can be transformed equatorial to horizontal, and horizontal to equatorial coordinate. It can measure the right ascension, declination, altitude and azimuth. It is composed of Sayu-hwan (Four displacements), Jeokdo-hwan (Equato.ial dial), Baekgak-hwan (Ring with one hundred-interval quarters), Gyuhyeong (Sighting aliadade), Yongju (Dragon-pillar) and Bu (Stand). So-ganui was used conveniently portable surveying as well as astronomical instrument and possible to determine time during day and night.

• Publications of The Korean Astronomical Society
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• v.31 no.3
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• pp.77-85
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• 2016

We study the manufacturers of the astronomical instruments invented as part of the so-called Ganui-Dae (astronomical platform) project in the reign of King Sejong (1418-1450) of the Joseon dynasty. The main purpose of this project was to compile the Chiljeongsan-Naepyeon, a Korean calendar, that lasted for 5.5 years from 1432 to 1438. Through this project, a total of 17 astronomical instruments such as the armillary sphere, celestial globe, and auto-striking clepsydra were developed. It is generally known that most of them were manufactured by Lee Cheon (李蕆, 1376-1451) and Jang Yeong-Sil (蔣英實, fl. 1423-1442). In this study, we investigate the accounts of the Veritable Records of King Sejong, Munjong, and Sejo, focusing on the inscription written out to memorize the completion of the Ganui-Dae project. We found that at least 12 persons took part in manufacturing the astronomical instruments of the Ganui-Dae project. Lee Cheon was involved in the production of four instruments, while Jang Yeong-Sil was involved in two; therefore, it seems that the achievement of Jang Yeong-Sil was overestimated. We also found that Jeong Cho (鄭招, ?-1434) was a scientist and Lee Cheon was an engineer in the early phase of the Ganui-Dae project, while King Sejong and Yi Sun-Ji (李純之, 1406-1465) played major role in the late phase. According to our study, King Sejong and Yi Sun-Ji were involved in the production of at least seven and five instruments, respectively. In conclusion, we believe that this study will be helpful to understand the practical manufacturers of the astronomical instruments invented during the Ganui-Dae project in the Joseon dynasty.

• Journal of Astronomy and Space Sciences
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• v.34 no.1
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• pp.45-54
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• 2017

This study examines the scale unique instruments used for astronomical observation during the Joseon dynasty. The Small Simplified Armillary Sphere (小簡儀, So-ganui) and the Sun-and-Stars Time-Determining Instrument (日星定時儀, Ilseong-jeongsi-ui) are minimized astronomical instruments, which can be characterized, respectively, as an observational instrument and a clock, and were influenced by the Simplified Armilla (簡儀, Jianyi) of the Yuan dynasty. These two instruments were equipped with several rings, and the rings of one were similar both in size and in scale to those of the other. Using the classic method of drawing the scale on the circumference of a ring, we analyze the scales of the Small Simplified Armillary Sphere and the Sun-and-Stars Time-Determining Instrument. Like the scale feature of the Simplified Armilla, we find that these two instruments selected the specific circumference which can be drawn by two kinds of scales. If Joseon's astronomical instruments is applied by the dual scale drawing on one circumference, we suggest that 3.14 was used as the ratio of the circumference of circle, not 3 like China, when the ring's size was calculated in that time. From the size of Hundred-interval disk of the extant Simplified Sundial in Korea, we make a conclusion that the three rings' diameter of the Sun-and-Stars Time-Determining Instrument described in the Sejiong Sillok (世宗實錄, Veritable Records of the King Sejong) refers to that of the middle circle of every ring, not the outer circle. As analyzing the degree of 28 lunar lodges (lunar mansions) in the equator written by Chiljeongsan-naepyeon (七政算內篇, the Inner Volume of Calculation of the Motions of the Seven Celestial Determinants), we also obtain the result that the scale of the Celestial-circumference-degree in the Small Simplified Armillary Sphere was made with a scale error about 0.1 du in root mean square (RMS).