The Angbuilgu Sundial, also referred to as the Hemispheric Sundial, was an important and widely used astronomical scientific device used to tell time. It was invented in 1434 during the 16th year of the reign of King Sejong. It got its name, Angbuilgu, from the pot shape design. It literally means “upward looking kettle that catches the shadow of the sun.”
The Angbuilgu has the shape of a hemisphere which helps express the shape of the sky. Even small sundials can be used to decipher time and seasons.
The gnomon, the triangular blade that casts its shadow, faces towards the north. There are also 13 horizontal and 7 vertical lines inlaid with silver which indicate time and seasons of the year.
The needle, known as yeongchim, indicates the true solar time. A correction is then used to adjust time to mean solar time which is used today.
These sundials were considered the first public time systems in Korea.