Song, I-Yeong (1619 ~ ?) was an active astronomer in the Joseon dynasty at the era of adopting the Shixian-li, Chinese calendar in Qing dynasty. His astronomical contribution was recorded in Annals of the Joseon Dynasty, Diary of the Royal Secretariat, Comparative Review of Records and Documents-Its Revision and Enlargement, and Treatise on the Bureau of Astronomy. In addition the details on his life and works were found at the genealogies of the Song Family from Yeonan and the Kim Family from Seonsan. His major astronomical activities can be summarized in three items. First, as a specialist astronomer, he has attempted to make a systematic observation of two comets. Second, he designed and fabricated the Jamyeong-jong, the weight-powered armillary clock, which became a typical model of the astronomical clock in the Joseon dynasty. Last, he served as a royal astronomical professor, greatly contributing on implementing the Shixian-li. Song has concentrated on performing astronomical duties for his royal official service time. Song is regarded as an important astronomer who made it possible to enforce the Shixian-li until the late Joseon dynasty.

There were two books on astronomy published in 1908. One is 『Astronomy (天文學)』 written by Jeong, Yeong-Taek (鄭永澤, 1874 ∼ 1948), an educator. The other is 『Introduction to Astronomy (텬문략히)』 written by William Martyn Baird (裵偉良, 1862 ∼ 1931), an American missionary. It was known that these two books were translated into Korean as astronomical textbooks of the Korean Empire. We investigated the life of translators, the motivation of writing textbook, and the translators’ specialty in astronomy. We also compared the two books in terms of content, orthography of terminology, scale of units, and so forth. We suggest that these books were really utilized as textbooks of astronomy in the modern school in the early 20th century in Korea. We also conclude that in astronomy education these two textbooks bridged the gap between the traditional Chinese astronomy of the middle age and modern astronomy from the West.

The royal astronomical observatory compiled the Astronomical Almanac during the Joseon dynasty, though there were some changes of its organization. However, the observatory underwent sudden changes in the late period mainly due to the influence of historical events such as the Gabo (甲午) and The Eulmi (乙未) Reforms in 1894 and 1895, respectively, and the Japanese invasion in 1910. In this paper, we study the changes of the compilation institution of the Korean Astronomical Almanac and of its organization for the period of 1894 to 1912. During this period, the name of the observatory had been changed several times, from Gwansanggam (觀象監) to Gwansangguk (觀象局) in 1894 and to Gwansangso (觀象所) in 1895. In addition, the affair of the Astronomical Almanac compilation was transferred to the Editorial Bureau [編輯局] of the Ministry of Education [學部] and to the Editing Department [編輯課] of the Governor-General of Korea [朝鮮總督府]. In 1907, the Gwansangso was abolished. Moreover, the affair of timekeeping was separated and the official number of personnel was reduced to less than 5% compared to that of Gwansanggam. Consequently, the royal astronomical observatory was significantly reduced in terms of its functions and the organization through the process of those changes. Therefore, we believe that this period is important when seeking to understand the transition between the traditional Astronomical Almanac of the Joseon dynasty and its modern astronomical counterpart of the present day.

During the Joseon dynasty, the Gwansanggam (觀象監, The Royal Astronomical Observatory) was the royal administration in charge of Astronomy (天文), Geography (地理), Calendars (曆), Astronomical and meteorological observation (測候), and Timekeeping (刻漏). Of those affairs, the Astronomical Almanac compilation was most important. In this paper, we study the education and selection of astronomical officials in the 19th century during the Joseon dynasty, focusing on Astronomical Almanac officials. According to this study, their main area was calendar calculation, and they were involved in Astronomical Almanac compilation for nearly 40 years, until they resigned. In addition, they served as Samryeok-susulgwan (三曆 修述官, Official for calendar calculation by the Shíxiàn calendar), and Ilgwa-gamingwan (日課監印官, Official printing supervisor). To undertake these core duties, an official had to pass several examinations and courses. The Gwansanggam (after Gwansangso) carried out the educational function for the officials. In particular, reserved officials of the astronomy division had to be educated starting with a trainee course.

We report the results of our study for ascertaining whether Ganui-dae built in the Josen Dynasty actually performed an astronomical role or not. The Ganui-dae was the first astronomical structure built as a part of the state astronomical undertakings by King Se-Jong. Our analysis was based on the Annals of the Joseon Dynasty. At first we extracted the records regarding Ganui-dae from the Annals of the Joseon Dynasty and then classified them under six heads according to their astronomical meaning and historical significance. From this analysis we found that the Ganui-dae performed the actual astronomical role. In addition, the provisional offices and peoples mentioned in the records show the astronomical correlation. Generally, when taking into account the functional side of the records, the Ganui-dae was related with the observation. Therefore, the Ganui-dae was the space for the astronomical activity. In conclusion, the Ganui-dae was built for the purpose of the astronomical activity.

Sambok (三伏, Three Hottest Days) is the common designation of Chobok (初伏, Early Hot Day), Jungbok (中伏, Middle Hot Day), and Malbok (末伏, Late Hot Day), and widely known to be one of the Korean folk customs. Hence, Sambok is notated in Manseryeok (Ten Thousand-Year Almanac) and in the annual astronomical almanac published by Korea Astronomy and Space Science Institute. In this paper, we investigate the changes of Sambok in Korea based on various documents such as Joseonwangjosilok (朝鮮 王朝實錄, Annals of the Joseon Dynasty), Jeungbo-Jakryeoksik (增補作曆式, The Supplement of Manual for Calendar Making), astronomical almanacs, and so forth. According to Jeungbo-Jakryeoksik preserved in Kyujanggak Institute for Korean Studies, Chobok and Jungbok are defined as the third and fourth Gyeongil (庚日, The Day Starting with the Seventh Heavenly Stems in Sexagenary Cycles Assigned to Each Day) after the summer solstice, respectively, and Malbok is the first Gyeongil after Ipchu (Enthronement of Autumn). However, if the summer solstice is Gyeongil, then the third Gyeongil counting from the solstice becomes Chobok. Malbok depends on the time of Ipchu. Ipchu itself becomes Malbok if the time of Ipchu is in the morning, or next Gyeongil becomes Malbok if it is the afternoon. On the other hand, Malbok is defined as Ipchu itself regardless of its time according to Chiljeongbobeob (七政步法, Calculating Method for Sun, Moon, and Five Planets), Chubocheobryeo (推步捷例, Quick Examples for Calendrical Calculations), and so on. To verify the methods used to determine Sambok, we examined the record in the extant almanacs during the period of 1392 to 2100 for which the summer solstice or Ipchu is Gyeongil. As a result, we found a periodicity that if the time of Ipchu is in the morning, in general, the time is in the afternoon after two years and then is back into in the morning after nineteen years, i.e., the 2 + 19 years periodicity. However, we found the 2 + 17 years periodicity in some years. We also found that the Chobok method of Jeungbo-Jakryeoksik has been used since 1712, the thirty-eighth reign of King Sukjong (肅宗). In addition, we supposed that Malbok had been determined by the method like Chubocheobryeo since either 1846, the twelfth reign of King Heonjong (憲宗), or 1867, the fourth reign of King Gojong (高宗). At present, these methods of Sambok are customarily used without any legal basis. We, therefore, think that this study will help conventionalize the method defining Sambok in the future.

Gyupyo (圭表, Gnomon) consists of Gyu (圭, Measuring Scale) and Pyo (表, Column), and was one of the traditional astronomical instruments in East Asia. Daegyupyo (Large Gnomon) was manufactured in the Joseon dynasty around 1434 ~ 1435. To increase the measurement accuracy, it was equipped with a Hoengyang (橫梁, Cross-bar) and used a Youngbu (影符, Shadow-Definer) which was invented during the Yuan dynasty (1271 ~ 1368). The cross-bar was installed on the top of the column and this structure was called Eol (臬). In addition, three plumbs hanging from the cross-bar was employed to vertically built Eol on the measuring scale. This method was also used to not only check the vertical of Eol but also diagnose the horizontal of the cross-bar. Throughout this study, we found that a cross-bar in a gnomon has played three important roles; measurement of the shadow length made by the central part of the Sun, increase of the measurement precision using the shadow-definer, and diagnosis of the vertical of Eol and the horizontal of the cross-bar itself using the three plumbs. Hence, it can be evaluated that the employment of a cross-bar and a shadow-definer in a gnomon was a high technology in the contemporary times. In conclusion, we think that this study is helpful for understanding the Large Gnomon of the Joseon dynasty.

Song I-Yeong (宋以頴, 1619 ~ 1692), who was an astronomy professor of Gwansanggam (觀象監, Bureau of Astronomy), created the Honcheonsigye (渾天時計, Armillary Clock) in 1669 (10th year of King Hyeonjong Era). Honcheonsigye was a unique astronomical clock which combined an armillary sphere, the traditional astronomical instrument of the Far East, with the power mechanism of western alarm clock. The clock part of this armillary clock is composed of two major parts which are the going-train, power unit used the weight, and the time signal system in a wooden case. The time signal system is composed of four parts which are the time-annunciator, the striking train, the 12 different time-announcing medallions and the sound bell. This clock has been neglected for many years and its several components have been lost. This study is to understand the structure of time signal system and suggests the restoration process.

The Ganui (簡儀, simplified armillary sphere) is a representative of astronomical instruments in Joseon Dynasty of Korea, as well as Yuan Dynasty and Ming Dynasty of China. In early 15th century, Joseon's scientists and engineers uniquely developed the Soganui (小簡儀, small simplified armillary sphere) and the Ilseongjeongsiui (日星定時儀, sun-and-star time determining instrument) from the structural characteristic of Ganui. These two astronomical instruments had a new design by the miniaturization and felt convinced a similar performance of Ganui in the harmony with Korean Astronomy and Astrology Cultures. Since mid-18th century after the enforcement of shixian-li (時憲曆), the Soganui and Ilseongjeongsiui handed over the Jeokdogyeongwiui (赤道經緯儀, equatorial armilla) by a change of the observational framework such as the time and angle measures. The Jeokdogyeongwiui made by Gwansanggam (觀象監, Bureau of Astronomy in Joseon Dynasty) adopted the new observational framework. We studied the structural characteristics and scientific values of these 3 astronomical instruments with theirs observation methods.

In this paper, we study the structure of the Daegyupyo (大圭表, Large Gnomon) of the early Joseon dynasty. A Gyupyo (圭表, Gnomon that is Guibiao as pronounced in Chinese) is composed of a Pyo (表, Biao as pronounced in Chinese) making a shadow and a Gyu (圭, Gui as pronounced in Chinese) measuring its length. It is known that the Daegyupyo with the 40-feet height was constructed between the sixteenth to seventeenth year of the King Sejong reign (1444 - 1445) on the basis of the record of Yuanshi (元史, the History of the Yuan Dynasty). By analyzing historical documents such as Joseonwangjosillok (朝鮮王朝實錄, the Annals of the Joseon Dynasty), Yuanshi, and Jegaryeoksangjip (諸家曆象集, a work written by Sunji Lee), we found a possibility that the Ji (池, a pond) on the Gyu was located in the north side of the Pyo. This structure is different from that in previous studies, but is in a good agreement with that of the 40-feet Guibiao remaining in Dengfeng (登封) of China. Regarding to the Hoengyang (橫梁, cross-bar), we suggest that it was set up by double 5-feet supporting arms apart from the north tip of the Pyo in the radial direction. The 3:4:5 ratio in a rectangular triangle was used to place the Heongyang on the top of the Pyo at a distance of 4-feet (3-feet) in the vertical (horizontal) direction. We also discuss the structural problem when the Hoengyang is positioned apart from the top of the Pyo by supporting arms. In conclusion, we think that this study should be useful in restoring the Daegyupyo of the Joseon dynasty.

In this paper, we have studied Sogyupyo (小圭表, small noon gnomon) of the Joseon dynasty. According to the Veritable Records of King Sejong (世宗, 1418 - 1450), Daegyupyo (大圭表, large noon gnomon) with a height of 40-feet [尺] was constructed by Jeong, Cho (鄭招) and his colleagues in 1435, and installed around Ganuidae (簡儀臺, platform of Ganui). On the contrary, the details of Sogyupyo are unknown although the shadow length measurements by Daegyupyo and Sogyupyo are found on the Veritable Records of King Myeongjong (明宗, 1545 - 1567). By analysing historical documents and performing experiments, we have investigated the construction details of Sogyupyo including its development year, manufacturer, and installation spot. We have found that Sogyupyo would be manufactured by King Sejong in 1440 and placed around Ganuidae. And Sogyupyo would be five times smaller than Daegyupyo, i.e., 8-feet. On the basis of experiments, we suggest that although it is smaller, Sogyupyo was equipped with a bar [橫梁] and a pin-hole projector [影符] like Daegyupyo in order to produce the observation precision presented in the Veritable Record of King Myeongjong.

Since the thirteenth century, large scale facilities and various instruments for astronomical observation were built and installed in East Asia. During the Yuan Dynasty, S. ti.ntai (Beijing astronomical observatory in the Yuan Dynasty, 司天臺) was built in Beijing in 1279. Various astronomical instruments, including Ganui (Jianyi, simplified armillary sphere, 簡儀), Yang-yi (upward hemisphere, 仰儀) and Gyupyo (gnomon, 圭表) were installed in this observatory. These astronomical instruments were modified and improved by researchers of the Joseon Dynasty. Ganuidae (Joseon astronomical observatory, 簡儀臺) was built in Gyeongbokgung (or Gyeongbok palace, 景福宮), Seoul. Its scale was 31 Cheok (Korean feet in the Joseon Dynasty, 尺) in height, 47 Cheok in length and 32 Cheok in width. Lee, Cheon (李蕆, 1376~1451), a responsible leader of Ganuidae project, set up various astronomical instruments with his colleagues. Ganui and Jeongbangan (direction-determining board, 正方案) were installed at the top of this observatory. Gyupyo was installed at the west side of this observatory and Honui (armillary sphere, 渾儀) and Honsang (celestial globe, 渾象) were installed in a small pavilion which was located next to Gyupyo. A decade after installation, this observatory was moved to the north-west side of the palace but almost destroyed during Japanese invasion of Korea in 1592 except Ganuidae. We have analyzed documents about Ganuidae and investigated Chinese remains of astronomical observatories and artifacts of astronomical instruments. In this paper, we suggest the appearance, structure, arrangement and scale of Ganuidae, which are expected to be used for the restoration of Ganuidae at some day in the near future.

In the beginning of the Joseon dynasty, the Royal Astronomical Bureau (觀象監, shortly RAB) was established. After the double RAB had settled down by King Sejong (世宗), it continued to function until 1907. Before the Japanese invasion of Korea in 1592, the Joseon court had the Inner RAB in the Gyeongbok Palace (景福宮) and the Outer RAB in the Northen District Gwangwha-Bang (北部廣化坊) at the western side of the Changdeuk Palace (昌德宮). In the reign of King Sukjong (肅宗) the double system of the RAB was transformed into the Geumho-Gate (金虎門) Outer RAB and the Gaeyang-Gate (開陽門) Outer RAB. During the reconstruction of the Gyeongbok Palace in the early reign of King Gojong (高宗), the Gaeyang-Gate Outer RAB was replaced by the Yeongchu-Gate (迎秋門) Outer RAB in 1865. All RAB had the Royal Astronomical Observatory (觀天臺, RAO hereinafter), so called the Soganui-platform (小簡儀臺) on which the Soganui (小簡儀) has been put. The Soganui (小簡儀) is a small simplified armillary sphere. While the Gwangwha-Bang RAO handed down from the reign of King Sejong still exists, other RAOs, such as Gyeongbok Palace RAO, Gaeyang-Gate and Yeongchu-Gate RAOs, do not remain. According to our study, the Changgyeong Palace (昌慶宮) RAO was not indeed the RAO with the Soganui.