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.

1. INTRODUCTION
 2. ANALYSIS OF THE LITERATURE
  2.1 Sun-and-Stars Time-Determining Instrument
  2.2 Simplified Time-Determining Instrument
  2.3 Simplified Sundial
 3. THE FOUR RINGS
  3.1 Sun-and-Stars Time-Determining Instrument
  3.2 Simplified Time-Determining Instrument
 4. RELATED RELICS
 4.1 External Properties and Usage
 4.2 Designation
 5. CONCLUSIONS
 REFERENCES

• Yong Sam Lee(Department of Astronomy and Space Science, Chungbuk National University, Cheongju 28644, Korea)
• Sang Hyuk Kim(Korea Astronomy and Space Science Institute, Korea University of Science and Technology) Corresponding Author
• Byeong-Hee Mihn(Korea Astronomy and Space Science Institute, Korea University of Science and Technology)