• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.181-184
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• 2006

Knowledge of the ionospheric peak parameter foF2 (the critical frequency of F2 layer) is one of key essential factors for predicting ionospheric characteristics and delay correction of satellite positioning. However, the foF2 was almost estimated using an empirical model of International Reference Ionosphere (IRI) or other expensive observing techniques, such as ionosondes and scatter radar. In this paper, the ionospheric peak parameter foF2 is the first observed by ground-based GPS with all weather, low-cost and near real time properties. Compared with the IRI-2001 and independent ionosondes at or near the GPS receiver stations, the foF2 obtained from ground-based GPS is in better agreement, but closer to the ionosonde. However, during nighttime, the IRI model overestimated the GPS observed values during winter and equinox months.Furthermore, seasonal variation trend of the foF2 in 2003 is studied using foF2 monthly median hourly data measured over South Korea. It has shown that the systematic diurnal changes of foF2 are apparent in each season and the higher values of foF2 are observed during the equinoxes (semiannual anomaly) as well as in mid-daytime of each season.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.48.4-49
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• 2018

We studyed an Korean astrolabe made by Ryu Geum (1741~1788), the late Joseon Confucian scholar. It has a diameter of 17 cm and a thickness of 6 mm and is now owned by Museum of Silhak. In the 1267 of the reign of Kublai Khan of Mogol Empire, Jamal al Din, an Ilkhanate astronomer, present an astrolabe to his emperor together with 6 astronomical instruments. In 1525, an astrolabe was first made in Korea by Lee, Sun (李純, ?~?), a Korean astronomer and royal official of Joseon Dynasty. He was referred to Gexiang xinshu, a Mongloian-Chinese book by Zhao, Youqin (1280-1345), an astronomer of Mongolian Empire. This astrolabe has not been left. In the mid-17th century, an astrolabe was introduced to Joseon again through Hungai tongxian tushuo (渾蓋 通憲圖設) edited by Chinese Mathematician Li Zhi-zao (李之藻, 1565~1630), that originated from Astrolabium (1593) of Christoph Clavius (1538-1612). It seems that Ryu refered to Hungai tongxian tushuo which affect to Hongae-tongheon-ui (渾蓋通憲儀) edited by Nam, Byeong-Cheol (南秉哲, 1817~1863). We analysis lots of circles on the mother and a set of index from the rete of of Ryu's astrolabe. We find that the accuracy of circles has about 0.2~0.4 mm in average if the latitude of this astrolabe is 38 degrees. 11 indices of the rete point bright stars of the northern and southern celestial hemisphere. Their tip's accuracies are about $2^{\circ}.9{\pm}3^{\circ}.2$ and $2^{\circ}.3{\pm}2^{\circ}.8$ on right ascension and declination of stars respectively.

• Journal of architectural history
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• v.15 no.1 s.45
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• pp.29-40
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• 2006

This paper is focused on Damheonseo(湛軒書), an anthology written by Hong Daeyong, and I deal with Chinese Architectural views which he had experienced in his itinerary to Beijing, and the vivid pictures of Joseonkwan (called the Koryo or Joseon Embassy) located in Beijing at that time. He was a scholar of great erudition over astronomy, mathematics, military science, politics, and so on. He was interested in practical sciences at early time, and criticized secular scholars full of vanity who had presented purposeless articles. In his age of 35, Qianlong(乾隆) 30 (1764, Youngjo 41), he, a military escort, accompanied by Hong Uk, Joseon envoy and his uncle. Before his itinerary, he self-studied Chinese. Also, during a long journey he got new experiences and information around each area, deviating his group whenever he had some times. He could get more variant experiences than others because of his character full of curiosity, and his observations from the vivid lives of the time helped us get various views between Chinese and Korean architecture. Likewise, although he denounced Qing(淸) scathingly as a barbarian, he mentioned several points about the characteristics of Chinese architecture at that time. First of all, totally Chinese architecture had strong rational and practical points. Secondly, based on bountiful products, buildings along streets shown in Chinese city had sophisticated compositions, and luxurious and magnificent appearances. Thirdly, using the brick from walls to houses was so universal. Fourthly, the layouts of building with three- or four-closed courtyard had very orderly shapes, and the structure of street was also so arranged. Finally, because of stand-up lives, the scales and appearances of interior space were even more extended, and storages were less developed than those of Joseon. As another points, I found that Joseonkwan was moved next to Shushangguan(庶常館)from Huidongnanguan(會同南館) around Hanlimyuan(翰林院), and had been remodeled into a house with Korean custom in using the inner spaces, although it was followed by a closed courtyard style. Likewise, I recognized that Ondols were sure to be established in all temporary houses during the journey to Qing, and felt their strong traditional residential custom in such mentions. Now that the past pictures have disappeared and ways of life and our values have been largely changed, this study has very important meaning in comparing the ancient Chinese and Korean architecture.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.52.1-52.1
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• 2012

It is often said that there is little geometrical mind in Korean history. However, a method to project the surface of a sphere onto 2-dimensional plain was applied to the representative Korean star chart or Cheonsang Yeolcha Bunyajido (天象列次分野之圖). The method, called the equi-distant polar projection, was explained in detail in ancient Chinese history book of the Tang dynasty, which was originated from older history. Another method of the Mercator projection was introduced by the famous engineer Su Song (蘇頌) of the Song dynasty. The description has quite geometrical thoughts, especially the concept of infinity or convergence appears, However, this type of sky projection method was not widely used in east Asia. When the European Jesuits came to China to evangelize the Chinese people, they found that the Chinese people paid much attention to advanced European astronomical knowledge. Thus, they introduced the European astronomical knowledges into China, and the star chart was one of them. The projection method of the new charts were quite different from the Chinese tradition. When the Koreans brought those new star chart from China, they must have known the geometrical description of the method. The method was described in detail in a volume of Chongzhen Lishi (崇禎曆書) or Xiyang Xinfa Lishu (西洋新法曆書). The explanation consists of three part. One is the quantitative way; another is a geometrical way using axiomatic systems; and the other is the practical method to draw star chart with the geometical projection. However, when we see the Honcheon Jeondo (渾天全圖) that is thought to be duplicated by Kim Jeongho (金正浩), the new geometrical method was not so widely known to the Koreans. I will discuss the reason why the geometrical minds have not been widely adopted in the Korean civilization.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.565-568
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• 2015

In this work, we study the correlation between the photon index (${\Gamma}$) of the X-ray spectrum and the 2-10 keV X-ray luminosity ($L_X$) for black hole X-ray binaries (BHBs). The BHB sample is mainly from the quiescent, hard and intermediate states, with values of $L_X$ ranging from ${\sim}10^{30.5}$ to $10^{37.5}$ erg $s^{-1}$. We find that the photon index ${\Gamma}$ is positively or negatively correlated with the X-ray luminosity $L_X$, for $L_X$ above or below a critical value, ${\sim}10^{36.5}$ erg $s^{-1}$. This result is consistent with previous works. Moreover, when $L_X{\leq}{\sim}10^{33}$ erg $s^{-1}$, we found that the photon index is roughly independent of the X-ray luminosity. We interpret the above correlations in the framework of a coupled hot accretion flow - jet model. Besides, we also find that in the moderate-luminosity region, different sources may have different anti-correlation slopes, and we argue this diversity is caused by the different value of ${\delta}$, which describes the fraction of turbulent dissipation that directly heats electrons.

• Journal of The Korean Astronomical Society
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• v.34 no.1
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• pp.47-57
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• 2001

In this paper we have reconstructed an armillary sphere based on the Method of an Armillary Sphere Making described in the Volume 1 of The Collection of Writings on the Scientific Instruments-Uigijipsol (儀器輯說, two volumes) edited in the 1850's by Nam Byong-Chul (南秉哲, 1817-1863) who was a famous Korean states-man-scientist. Nam achieved convenience and accuracy in the measurements of stellar positions in the manner of selective setting the equatorial, ecliptic and horizontal poles by adding a pole axis exchange ring called Jaigeukkwon (載極圈) between the Three Arrangers of Time and Four Displacements. We made use of 3-dimensional graphic software for modelling Nam's armillary sphere which consisted of five layers-eight rings. Results of simulation showed that the pole axis exchange ring functioned properly in setting the equatorial, ecliptic and horizontal coordinates simply by exchange of positions of specified holes on the ring. We ascertained that the invention of Jaigeukkwon solved inherent problems in the conventional Chinese armillary sphere in computation of real ecliptic coordinates. It was revealed that Nam Byong-Chul made great contributions in the East Asian history of armillary sphere making.

• Publications of The Korean Astronomical Society
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• v.31 no.1
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• pp.1-9
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• 2016

We investigate the records related to the reign style and the calendar day from the epigraphs of the Goryeo dynasty (918 - 1392) in Korea in order to verify and supplement the sexagenary cycle data of the first day in the lunar month of the dynasty. The database of the National Research Institute of Culture Heritage contains a rubbed-copy image, transcription statement, and translation statement for Korean epigraphs as well as 775 epigraphs corresponding to the Goryeo dynasty. The epigraph records are valuable in that, during this time, they were written differently from other historical literature such as the Goryeosa (History of the Goryeo Dynasty), which was compiled in the next dynasty. We find that the Goryeo dynasty, in general, had adopted the reign styles of Chinese dynasties at that time. We also find 159 calendar day records all showing good agreement with the work of Ahn et al. except for dozens of records. Through this study, we can verify the reign styles and the calendar days of the Goryeo dynasty.

• Publications of The Korean Astronomical Society
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• v.27 no.5
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• pp.411-418
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• 2012

We study the correlation between distributions of astronomical records and historical events using historical meteor (shower) records. In Korean chronicles, planets and meteor (shower) records are the most abundant astronomical phenomena. And they represent a general tendency of the number distribution of whole astronomical observations. We examine the correlation for the number distribution between meteors (showers) and planets during A.D. 1200-1700 and find that both records have a similar distribution. We classify historical events into three grades according to the social impact, and investigate the correlation between distributions of meteor (shower) records with social events, such as, new king's accession to the throne, foreign invasions, and domestic turmoils. From the statistical analysis, we cannot find any correlation between the meteor (shower) records and the political events. Therefore, we conclude that Korean historical records have not been influenced by the political events. We also examine the correlation between Chinese and Japanese meteor (shower) records and political events for A.D. 1200-1700, respectively, but cannot find any correlations between them.

• 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.38 no.3
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• pp.147-160
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• 2023

In this study, we explore and catalog Korean astronomical heritages that are known to be preserved in foreign countries. We exclude old astronomical books from the catalog because they have been well studied and exist in numbers far too large for the scope of this study. From various documents and online collections, we find a total of 38 Korean astronomical heritages in six countries: 10, 11, and 14 items from the UK, France, and Japan, respectively, and 1 item from Germany, the US, and China each. These include items that are suspected to be of Chinese heritage and items of unconfirmed possession status. We divide the astronomical heritages primarily into two groups: time-keeping instruments (18 items) and astronomical charts (20 items). In this paper, we briefly review them according to country. We believe that this study provides a foundation for further detailed studies on each item, such as the Gujang-Cheonsang-Yeolcha-Bunya-Jido (舊藏天象列次分野之圖) preserved in the Library of Congress, United States.