Pyeonghonui`(Astronomical Observation Instrument)

This circular star chart made by the renowned Silhak scholar Bak Gyu-su (1807-1877) shows the constellations in both the northern and southern hemispheres, and is designed to help measure time and the seasons through the positions of the constellations. The chart is based on the traditional armillary sphere called a Honcheonui developed in East Asia, a two-dimensional (i.e. a plane circle) map simplified from a three-dimensional work (i.e. a sphere). The name of the map, Honpyeongui, was given by Nam Byeong-cheol (1817-1863), who also revealed that the map was "made by my friend Bak Hwangyeong" [Bak Gyu-su's courtesy name].
Drawn by Bak Gyu-su on cardboard, the map features a disk with a diameter of 34 centimeters, and was placed in a paper container with the following postscript: "A small version of the hand-made star map contained." The chart consists of a double-face, with the northern face containing the constellations of the northern hemisphere star and the southern face containing those of the southern hemisphere. Each face is then divided into upper and lower discs, of which the lower disc is designed to rotate and marked with lines representing longitude, latitude, and the ecliptic. The lower disc of the northern face contains the stars (magnitude 6 and brighter) of the northern hemisphere while the lower disc of the southern face contains the stars (also magnitude 6 or brighter) of the southern hemisphere. The star chart made into a brass instrument is currently on public display in the National Palace Museum of Korea under the title Astronomical Observation Instrument. Considering the elaborate technique with which the constellations are meticulously engraved on the brass disc with a diameter of 34 centimeters, the considerable expenditure of money on the instrument, and the 77.5-centimeter-tall wooden rack supporting it, the star chart in Deoksugung Palace is believed to have been created by the government under the supervision of Nam Byeong-cheol, probably in the 1850s, when he and Bak Gyu-su were keenly interested in astronomical observation and related instruments.