Credits

astronomy-engine by Don Cross, MIT licence: the Sun's apparent longitude for the solar terms and the equation of time.
GeoNames (geonames.org), Creative Commons Attribution 4.0: the list of birthplaces with coordinates and time zones.
IANA time zone database, public domain, through your browser: historical clock offsets, including Korea's UTC+8:30 periods and summer time.
Noto Serif KR and IBM Plex Sans KR, SIL Open Font License 1.1, served by Google Fonts.
Solar term times used to test the engine: Hong Kong Observatory, Date and Time of the 24 Solar Terms.
Reference charts used to test the engine: lunar-javascript by 6tail (MIT), used in testing only.