Sundials

Ganpyeongilgu and Hongaeilgu are two sundials of an unusual form, engraved together on a single stone. An inscription records that they were made in 1785, calculated on the basis of Seoul's latitude of 37 degrees 39 minutes 15 seconds and a polar distance between the ecliptic and the equator of 23 degrees 29 minutes. The Ganpyeongilgu sundial is, in effect, the design of the Angbuilgu sundial projected directly onto a horizontal plane; it measures 129 cm long, 52.2 cm wide and 12.3 cm thick. The diameter of its sundial face is 43 cm. The centre of the flat circle is inscribed as the zenith, and the point from which the time lines radiate is inscribed as the North Pole; by aligning the instrument to this North Pole, one could read off the sun's motion overhead together with the time. The Hongaeilgu sundial has a face 46 cm in diameter. On both dials, curved vertical and horizontal lines are drawn within the circle, the vertical lines marking the hours and the horizontal lines marking the seasons. The gnomon at the centre is half the length of the circle's diameter, and the time can be read from the changing position of its shadow. Because the sun's noon altitude differs with each solar term, the 24 solar terms of the traditional calendar can also be read from the differing length of shadow falling on the seasonal lines. On both dials the lines of the sundial face are accurate and finely drawn, and the skill with which these delicate lines have been incised into the stone is outstanding. Dignified in character and unusual in structure, these sundials are of great heritage value.

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Where it is

Region

Jongno-gu, Seoul

Designation

Treasure · 보물