Daylight Visibility of Jupiter with the Naked Eye

This study examines Korean historical records of daylight sightings of Jupiter to estimate the empirical limiting magnitude for observing celestial bodies without optical aid during daylight. Using sources such as Joseonwangjo-Sillok (The Veritable Records of the Joseon Dynasty), Seungjeongwon-Ilgi (The Daily Records of the Royal Secretariat of the Joseon Dynasty), and Donggung-Ilgi (The Daily Records of the Royal Education Bureau for the Crown Prince of the Joseon Dynasty), we identified 40 instances of daylight observations of Jupiter during the Joseon dynasty (1392–1910). Employing astronomical algorithms and modern ephemeris, we calculated sunrise, solar transit, and sunset times to identify the observation hour, confirming whether the events occurred during daytime or twilight. Additionally, we determined the azimuth and magnitude of Jupiter during each recorded event to verify the direction and brightness of the observed phenomenon. Our analysis yielded the following key findings: (1) The records of daylight sightings of Jupiter are concentrated in the 16th and 17th centuries, corresponding to prolonged periods of solar activity minima. (2) These observations occurred during broad daylight rather than twilight. (3) The limiting magnitude for unaided daylight observations of a celestial body is at least –2.1.