Two-in-one Sundial Made by the Royal Astronomical Bureau

Sundials are placed side by side on a stone slab: one sundial on which lines are carved around the north pole (which is called the Ganpyeongsundial) and the other sundial on which lines of longitude and latitude are carved around the south pole (Hongaesundial). The vertical and horizontal lines of the Ganpyeong sundial indicate time and twenty-four fortnightly periods respectively. The vertical lines of the Hongaesundial, with incremental distances between each other, represent time, while the bottom of the centerline points to the south indicates noon. This relic has an inscription suggesting that it was made in 9th year of King Jeongjo’s reign in Joseon, the latitude of Hanyang was measured at 37°39´15˝ N, and the polar distance from the ecliptic and the equator at 23°29′ was a reference value for measurement in accordance with the Chinese lunisolar calendar.