• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.138.2-138.2
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• 2011

Astronomical data such as calendar day and time of rising/setting of the sun and onset of twilight are essential in our daily lives. Knowing the calendar day of the past is particularly crucial for studying the history of a clan or a nation. To verify previous studies on the calendar day of the Joseon dynasty (1392 - 1910), we also investigated the sexagenary cycle of the new moon day (i.e., the first day in a lunar month) using different sources: results of the calculation by the Datong calendar (a Chinese Calendar of the Ming Dynasty) and data of Baekjungryeok (a Perpetual Calendar - literally, a one hundred-year almanac). Compared with the study of Ahn et al., we have found that as many as 17 sexagenary cycles show discrepancies. In the case of nine discrepancies, we found that the sexagenary cycles of this study are identical to those of the almanacs at that time. In addition, we study six sexagenary cycles by using the historical accounts of Joseon Wangjo Sillok (Annals of the Joseon Dynasty), Seungjeongwon Ilgi (Daily Records of Royal Secretariat), Chungung Ilgi (Logs of Crown Prince), and so forth. We present historical materials supporting the results of this study for the remainder. In conclusion, we think that this study will greatly contribute to the comparison between luni-solar calendar days during the Joseon dynasty and those in the modern (i.e., Gregorian) calendar.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.591-592
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• 2015

X1822-371 is a low mass X-ray binary with an accretion disk corona exhibiting partial eclipses and pulsations in the X-ray band. We update its orbital ephemeris by combining new RXTE observations and historical records, with a total time span of 34 years. There were 11 RXTE observations in 2011 but the eclipsing profile can be seen in only 4 of them. The eclipsing center times were obtained by fitting the profile with the same model as previous studies. Combined with the eclipsing center times reported by Iaria et al. (2011), the O-C analysis was processed. A quadratic model was applied to fit the O-C results and produced a mean orbital period derivative of $\dot{P}_{orb}=1.339(25){\times}10^{-10}s/s$, which is slightly smaller than previous records. In addition to the orbital modulation from the orbital profile, we also present our preliminary results for measuring the orbital parameters using the orbital Doppler effect from the pulsation of the neutron star in X1822-371. The updated orbital parameters from eclipsing profiles will be further compared with the ones from pulsar timing.

• Journal of Astronomy and Space Sciences
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• v.30 no.3
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• pp.187-192
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• 2013

Honsangui (celestial globe) which is a water-hammering method astronomical clock is recorded in "Juhaesuyong" which is Volume VI of supplement from "Damheonseo", written by Hong Dae-Yong (1731~1783). We made out the conceptual design of Hong Dae-Yong's Honsangui through the study on its structure and working mechanism. Honsangui consist of three rings and two layers, the structure of rings which correspond to outer layer is similar to his own Tongcheonui (armillary sphere) which is a kind of armillary sphere. Honsang sphere which correspond to inner layer depicts constellations and milky way and two beads hang on it as Sun and Moon respectively for realize the celestial motion. Tongcheonui is operated by the pendulum power but Honsangui is operated by water-hammering method mechanism. This Honsangui's working mechanism is the traditional way of Joseon and it was simplified the working mechanism of Shui y$\ddot{u}$n i hsiang t'ai which is a representative astronomical clock of China. This record of Honsangui is the only historical record about the water-hammering method working mechanism of Joseon Era and it provide the study of water-hammering method mechanism with a vital clue.

• Journal of Astronomy and Space Sciences
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• v.27 no.1
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• pp.55-68
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• 2010

It has been generally known that Datong-li (a Chinese calendar in the Ming dynasty) was first introduced into Korea in the nineteenth reign of King Gongmin (1370) of the Goryeo dynasty and lasted to the third reign of King Hyeojong (1652) of the Joseon dynasty. This understanding is based on the records of Goryeo-sa (History of the Goryeo dynasty) and of Seoungwan-ji (Official book of Seoungwan)/Jeungbomunheon-bigo (Explanatory Notes of Library Document). To verify the period of the use of Datong-li in Korea, we develop a Fortran code to calculate the calendar day by Datong-li and also investigate historical literatures and extant almanacs. As a result, we find the possibility that Datong-li had been in use since 1389 at least. However, we cannot confirm whether Datong-li was first enforced in 1370 or not. On the other hand, we confirm that Datong-li was used until 1653 and reintroduced during the period from 1667 to 1669. Also, we find that previous studies had some errors in the sexagenary cycle of the real first day of a month. We think that this study will contribute to understanding the calendrical history of the Joseon dynasty.

• Publications of The Korean Astronomical Society
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• v.29 no.2
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• pp.17-27
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• 2014

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.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.24.2-24.2
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• 2009

We present the results of new CCD photometry for the contact binary BX Peg, made during three successive months beginning on September 2008. As do historical light curves, our observations display an O'Connell effect and the November data by themselves indicate clear evidence for very short-time brightness disturbance. For these variations, model spots are applied separately to the two data set of Group I (Sep.--Oct.) and Group II (Nov.). The former is described by a single cool spot on the secondary photosphere and the latter by a two-spot model with a cool spot on the cool star and a hot one on either star. These are generalized manifestations of the magnetic activity of the binary system. Twenty light-curve timings calculated from Wilson-Devinney code were used for a period study, together with all other minimum epochs. The complex period changes of BX Peg can be sorted into a secular period decrease caused dominantly by angular momentum loss due to magnetic stellar wind braking, a light-travel-time (LTT) effect due to the gravitational effect of a low-mass third companion, and a previously unknown short-term oscillation. This last period modulation could be produced either by a second LTT orbit with a period of about 16 yr due to the existence of a fourth body or by the effect of magnetic activity with a cycle length of about 12 yr.

• Publications of The Korean Astronomical Society
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• v.33 no.2
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• pp.9-19
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• 2018

We investigate the life of Lee Cheon (1376-1451) who was closely connected with astronomy during the reign of King Sejong of the Joseon dynasty. Lee Cheon is widely regarded as one of the outstanding scientists of King Sejong's period. However, his contributions to the development of the astronomy during the period have not been enlightened. Based on the historical records on the life and achievements of Lee Cheon, mainly referring to the Joseonwangjosillok (Annals of the Joseon Dynasty), we address three important points. First, Lee Cheon was a distinguished administrator who filled various government posts. Second, he was a supervising engineer in public works and metal smelting during his position in military. Third, he was a scientific technician and manufactured precision equipment such as the metal movable type sets. By virtue of these aspects, Lee Cheon was taken into confidence by King Sejong on the Ganui-dae project (i.e., manufacture various astronomical instruments and construct their platform in order to make a calendar suitable for Joseon). During the period of this project, Lee Cheon not only supervised the construction of the Ganui (simplified armillary sphere) and Ganui-dae (platform for astronomical instruments) but also participated in the production of the astronomical instruments such as Gyupyo (Gnomon) and Honcheonui (Armillary Sphere). In conclusion, we regard Lee Cheon as one of the astronomers who led a great advance in astronomy during King Sejong's era.

• Publications of The Korean Astronomical Society
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• v.32 no.3
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• pp.407-420
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• 2017

We study the operation of a lunisolar calendar in Korea and its time data calculation method. The dates based on the lunisolar calendar have been conventionally used in Korea after the Gregorian calendar was introduced in 1896. With the Astronomy Act enacted in 2010, the lunisolar calendar is presently being used as an official calendar along with the Gregorian calendar. However, no institutionalized regulations have been provided on the time data calculation method by the lunisolar calendar. The Korea Astronomy and Space Science Institute very recently established the regulations on the lunisolar calendar operation in Korea. We introduce the regulations together with historical substances and analyze the time data calculated according to the regulations for 600 years from 1901 to 2500. From our study, we find that the value of ${\Delta}T$ (i.e., the difference between the terrestrial time and the universal time) is the most critical parameter causing uncertainty on the data. We also find that all new Moon days in the almanacs agree with our calculations since 1912. Meanwhile, we find that new Moon and winter solstice times are found to be very close to midnight in 38 and five cases, respectively. For instance, the new Moon time on January 14, 2097 is 0 h 0 min 8 s. In this case, deciding the first day (i.e., new moon day) in a lunar month is difficult because of the large uncertainty in the value of ${\Delta}T$. Regarding with a lunar leap month, we find that the rules of inserting the leap month do not apply for 17 years. In conclusion, we believe that our findings are helpful in determining calendar days by using the lunisolar calendar.

• Publications of The Korean Astronomical Society
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• v.17 no.1
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• pp.23-40
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• 2002

The spatial distribution of meteoroids or cometary debris along the orbit of the Earth is investigated by analyzing the meteoric records in the Chronicle of the Koryo dynasty (918-1392) which is called Koryosa. Sporadic meteors in this period show the seasonal variation in number, which is similar to the current meteors. We also found that there are a few spikes showing large accumulation of records around the same dates. We regard these spikes as meteor showers in the Koryo period. We compared the dates of meteor showers with those compiled from the historical records around the world including Korea, Japan, China, Arab, and European countries. We discovered three prominent showers and four weak showers. The prominent ones are the Leonids, the Perseids, and the Aquarids and the Orionids pair. The last pair is the remnants of Halley's comet. The astronomical records written in the history book of the Koryo dynasty are turned out to be accurate and written in a steady manner. We can also see that those records can be useful to contribute the development of modern astronomy and astrophysics.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.38.2-38.2
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• 2008

In Korean historical documents, there are a great number of the records for various astronomical events. In particular, historical documents of the Joseon dynasty also have the records containing observational data by an astronomical instrument. However, a quantitative analysis for the accuracy of observational values have never been studied, although there are some studies on the truth of the records themselves. Hence, we investigated observation errors during the period of the Joseon dynasty from the records of Joseon-Wang-Jo-Sil-Lok (the Annals of the Joseon Dynasty) and Seung-Jeong-Won-Il-Gi (Daily Records of the Royal Secretariat). We used the records of the Mars, supernova 1604, and Halley's Comet, and found that observational values before the Hideyoshi invasions in 1592 are relatively more accurate than those after then. However, because the number of cases used in this study is small, we think that more studies are needed to confirm our results. Nonetheless, we reckon our work will be of service to understand astronomical records of the Joseon dynasty.