In March 2022, Wongu-ilyeong, a globe-like sundial made during the 19th century in the Joseon Dynasty, was repatriated from the United States through the efforts of the Korea Heritage Service and the Overseas Korean Cultural Heritage Foundation. This sundial has a total height of about 228 mm, and has time lines and a T-shaped gnomon on its spherical surface with a diameter of approximately 112.2 mm. This sundial is known to have been made by Sang Jik-Hyeon (尙稷鉉, 1849–?), as he carved his seal and the manufacturing date onto its spherical surface. This study investigated Sang, Jik-Hyeon's records from royal governmental literature, and also analyzed the structure of Wongu-ilyeong to understand its usage. We restored the Wongu-ilyeong’s design drawing and manufactured a prototype, with which we measured daytime hours in Jeju, Daejeon, and Seoul. The experimental measurements from three cities showed that the time accuracy of the Wongu-ilyeong, whose minimum time scale is 15 minutes, could be measured within ±7.5 minutes. Wongu-ilyeong is a very rare type of sundial-relic in Korea and overseas, and it is considered to have significant value in the history of science and technology.

This study employs a range of AI-based bibliometric methods to examine trends among astronomical research publications. Astronomy is a field with a long history of research and a wide variety of fields, so there are many areas in which quantitative bibliometric studies can be used to categorize topics, summarize research trends, and explore future research directions. For our first attempt we chose the oldest astronomical instrument, the sundial. We collected a total of 172 sundial and gnomon research papers from 1909 to 2024 from Web of Science and Scopus databases. A bibliometric analysis of the astronomical research papers was performed using the bibliometrix package in R. Topics were categorized and discussed using the Structural Topic Model (STM) method. Productivity, citation counts, and other metrics were compared across countries and journals and the global network of researchers engaged in the study of sundials was analyzed. Results emphasize the need for greater international collaboration and interdisciplinary integration. Current trends in sundial and gnomon research were reviewed, identifying eight research topics through the use of STM, demonstrating the evolution of this field into various applications. The article concludes by discussing future research directions for sundials and gnomons, demonstrating the applicability of AI-assisted bibliometric analysis in various fields of astronomy research.

We analyze the design and specifications of the Sun-and-Stars Time-Determining group of instruments (Ilseong-jeongsi-ui, 日星定時儀) made during the Joseon dynasty. According to the records of the Sejong Sillok (Veritable Records of King Sejong), Sun-and-Stars Time-Determining Instruments measure the solar time of day and the sidereal time of night through three rings and an alidade. One such instrument, the Simplified Time-Determining Instrument (So-jeongsi-ui, 小定時儀), is made without the essential component for alignment with the celestial north pole. Among this group of instruments, only two bronze Hundred-Interval-Ring Sundials (Baekgak-hwan-Ilgu, 百刻環日晷) currently exist. A comparison of the functions of these two relics with two Time-Determining Instruments suggests that the Hundred-Interval-Ring Sundial is a Simplified Sundial (So-ilyeong, 小日影), as recorded in the Sejong Sillok and the Seongjong Sillok (Veritable Records of King Seongjong). Furthermore, the Simplified Sundial is a model derived from the Simplified Time-Determining Instrument. During the King Sejong reign, the Sun-and-Stars Time-Determining Instruments were used in military camps of the kingdom’s frontiers, in royal ancestral rituals, and in royal astronomical observatories.