Ganpyeongui

Ganpyeongui (簡平儀) is a scientific artifact from the Joseon period, held by the Seoul Museum of History in Jongno District, Seoul, which is used to observe time and the celestial calendar (天體曆). It was designated as Tangible Cultural Heritage No. 163 of Tangible Cultural Heritage of Seoul on December 26, 2002.

Overview

The Ganpyeongui held by the Seoul Museum of History is known as a scientific artifact used to observe time and the celestial calendar, and it is the first of its kind discovered in Korea. The Ganpyeongui is said to have first been made in 1680 (the 19th year of the Kangxi era) by Western missionaries who had come to China. In Korea, it is said that in the period from 1752 to 1762, the Silhak scholar Hong Taeyong (湛軒 洪大容, 1731–1783) of the reign of King Yeongjo, after returning from China, made an instrument called the cheukgwan (測管) inside the Nongsugak (籠水閣), a private observatory of his own making. This is said to be Korea's first Ganpyeongui, although the actual object has not survived. The "pyeong-ui" (平儀) refers to an instrument that projects the sky onto a flat surface, unlike round, sphere-shaped instruments such as the terrestrial globe (地球儀) or the armillary sphere (渾儀), which are spherical instruments (i.e., celestial globes). The name "Ganpyeongui" (簡平儀) was given because it made such a flat instrument even simpler.

This Ganpyeongui has a disc-shaped brass plate on which the front and back surfaces display constellations, the 24 solar terms, the five night watches (五更), a calendar for the year, and so on. The front side consists of two plates. The lower one is the celestial disk (天盤), engraved with the northern hemisphere constellations, the southern hemisphere constellations up to a declination of about 52°, the celestial equator, and the ecliptic. The one placed on top is the horizon disk (地盤), which shows the horizon, the meridian, and other lines. A part of the horizon disk is cut out in a circle, and the two plates are rotated and combined so that the constellations can be identified. The back side has a structure in which a disc of 5.6 cm in diameter, engraved with the 12 earthly branches (干支), is placed on a disc displaying time, the 24 solar terms, and a calendar dial, and it is designed so that night time can be measured according to the solar terms. The structure of this instrument is similar to the Chinese Ganpyeongui made in 1680 (the 19th year of the Kangxi era), and the back side in particular is identical. However, the front side differs in the constellations shown near the center of the celestial disk. The Ganpyeongui in the Seoul Museum of History shows the declination of stars due south of the horizon as about 52°, which, considering that this is the range within which stars culminating in the south can be observed from Hanyang, indicates that it was manufactured in Korea. This instrument is the first Ganpyeongui artifact found in Korea, and its craftsmanship is precise, giving it great astronomical and history-of-science value.