• 천문학회지
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• 제53권6호
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• pp.125-138
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• 2020

We determine the observing sites for eclipses of large magnitude recorded in ancient Chinese chronicles from 200 BCE to 900 CE, by adopting the difference between terrestrial time and universal time, ΔT, given by Morrison & Stephenson (2004). The records of solar eclipses with large magnitude are divided into four groups in accordance with the historical variations of the capital cities of ancient Chinese dynasties. We determine areas in which all the eclipses in each group, with an eclipse magnitude larger than a certain threshold value, could be observed. We find that these areas coincide with the historical capitals, which agrees with the general idea that the solar eclipses were observed at the capital of each dynasty. This result also verifies the ΔT values during the period from 100 BCE to 400 CE, during which historical records of eclipses are so rare that the ΔT values can only be obtained by interpolating the long-term data. Moreover, we show that the eclipses described by the term Ji in East-Asian history are not all total eclipses; their mean magnitude is 0.96 ± 0.04. We find that complementary expressions, such as dark daytime and appearance of stars during the eclipse, strengthen the possibility that eclipses described by the term Ji were total. We also provide quantitative definitions for expressions such as 'being not complete and like a hook', 'being almost complete', 'visibility of stars during the eclipse', and 'darkness during an eclipse.' The literal meanings of these expressions are in agreement with the recent physical modeling of sky brightness during total eclipses provided by Können & Hinz (2008).

• 천문학논총
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• 제23권2호
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• pp.65-71
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• 2008

It has been considered that 'exhausted eclipses' (日食旣) were total eclipses. However, modern precise calculations show that a significant fraction of such records are not realized to be total. Thus we doubt that the two concepts are equivalent. Here we investigate the meaning of 'exhausted eclipses' in the east-Asian history. We first find that eclipses of magnitude greater than 0.8 were regarded as 'exhausted eclipses' by a Korean astronomer of the 18th-century Choson dynasty. His notion was based upon the definition of 'exhausted eclipses' in the ephemerides of pre-modern Chinese dynasties. According to those ephemerides, the 'exhausted eclipses', whose magnitude is greater than 0.8, have the first contact at the western part of the solar disk and the fourth contact at the eastern part of the solar disk. A simple geometrical calculation shows that such cases really occur when the magnitude of eclipse is greater than 0.7. We pointed out that such an ancient definition might not be impractical for ancient astronomers, because the uncertainty of eclipse magnitude estimated by ancient Chinese ephemerides was 10% and the human sight has a spatial resolution of 1.2 arcmin, which is approximately one twentieth of the Sun's angular diameter.

• 천문학회지
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• 제49권4호
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• pp.163-173
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• 2016

In this paper, we study the lunar eclipse records in the Goryeosa (History of the Goryeo Dynasty), an official history book of the Goryeo dynasty (A.D. 918 - 1392). In the history book, a total of 228 lunar eclipse accounts are recorded, covering the period from 1009 to 1392. However, we find that two accounts are duplications and four accounts correspond to no known lunar eclipses around the dates. For the remaining lunar eclipses, we calculate the magnitude and the time of the eclipse at different phases using the DE406 ephemeris. Of the 222 lunar eclipse accounts, we find that the minimum penumbral magnitude was 0.5583. For eclipses which occurred after midnight, we find that some accounts were recorded on the day before the eclipse, like the astronomical records of the Joseonwangjosillok (Annals of the Joseon Dynasty), while others were on the day of the lunar eclipse. We also find that four accounts show a difference in the Julian dates between this study and that of Ahn et al., even though it is assumed that the Goryeo court did not change the dates in the accounts for lunar eclipses that occurred after midnight. With regard to the contents of the lunar eclipse accounts, we confirm that the accounts recorded as total eclipses are accurate, except for two accounts. However, both eclipses were very close to the total eclipse. We also confirm that all predicted lunar eclipses did occur, although one eclipse happened two days after the predicted date. In conclusion, we believe that this study is very helpful for investigating the lunar eclipse accounts of other periods in Korea, and furthermore, useful for verifying the calendar dates of the Goryeo dynasty.

• Journal of Astronomy and Space Sciences
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• 제15권2호
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• pp.449-458
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• 1998

다목적실용위성은 고도 685km의 태양동기궤도를 임무 궤도로 사용하며, 궤도 당 약 34~35분씩 지구에 의해 태양 빛이 가리는 식 현상과 비 주기적으로 달에 의한 월식 현상이 발생한다. 위성의 월식은 달이 태양과 위성 사이에 위치하여 위성에 도달하는 태양 빛을 전체 혹은 부분적으로 가리는 것을 의미한다. 식 현상은 위성 체의 배터리 충전 및 방전 회수를 증가시키며 위성의 수명과 임무 및 운용에 영향을 준다. 다목적 실용위성은 주기적인 지구의 식 현상을 고려하여 설계되었으나 월식이 일어나는 경우 위성 체의 에너지 균형과 배터리 방전에 대한 부수적인 효과와 함께 운용상의 문제를 초래할 수 있다. 본 연구에서는 다목적실용위성의 임무 기간인 3년 동안 위성 운용 중에 발생할 수 있는 월식 현상을 예측하고 이에 대비한 임무 계획을 제시하였다.

• 천문학회보
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• 제43권1호
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• pp.49.5-50
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• 2018

Korean chronicles have a large amount of observational records over two thousand years. Many historical astronomical records are useful in modern times. In this study, we examined solar eclipses in Goguryeo-bongi(高句麗本紀) by using the modified(newest) nutation value and reviewed the observation area through eclipsing map. There are 11 solar eclipse records in the book. We calculated intersectional visible area with 0.6 eclipsing magnitude using the records of AD116, 124, 149, 158 and 219 and found the observational area of $N40-43^{\circ}$ and $E123-127^{\circ}$, which corresponds to the Liaodong(遼東). We also examined historical Chinese solar eclipse records and compared them with Korean eclipses.

• 천문학회지
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• 제29권spc1호
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• pp.439-440
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• 1996

The Chinese ancient accounts of timing observations of 48 lunar eclipses and the secular variation of the Earth's spin speed are discussed. A series of ${\Delta}$T expressing the secular deceleration of the Earth's rotation was obtained. The average increase rate of length of the day is about 1.5 milliseconds per century.

• 천문학회지
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• 제26권2호
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• pp.135-139
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• 1993

Events of eclipses as well as other major astronomical events observable in the eastern sector of Asian continent are computed and checked with astronomical records of antiquity. Particular attention was given to two types of the events recorded in remaining records of Dangun Chosun Period (DCP): (1) concentration of major planets near the constellation of Nu-Sung $(\beta\;Aries)$ and (2) a large ebb-tide. We find them most likely to have occurred in real time. i.e., when the positions of the sun, moon, and planets happen to be aligned in the most appropriate position. For solar eclipses data, however, we find among 10 solar eclipse events recorded, only 6 of them are correct up to months, implying its statistical significance is no less insignificant. We therefore conclude that the remaining history books of DCP indeed contains important astronomical records, thereby the real antiquity of the records of DCP cannot be disproved.

• 천문학회보
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• 제37권1호
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• pp.100.1-100.1
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• 2012

Lunar limb profiles are needed for analyses of lunar occultations and solar eclipses. The lunar limb profile data by C.B. Watts (1963) have been used for such analyses, but it has been found that there are many kinds of errors in the data by Watts, which seriously affected the results obtained from the analyses of the observations. Recently very precise lunar topographic data were obtained by the Japanese lunar explorer Kaguya and NASA's Lunar Reconnaissance Orbiter. I obtained lunar limb profiles for any lunar librations from them. I will show how well the lunar limb profiles fit to observed ones from lunar grazing occultations. By combining the accurate lunar limb profiles with observations of lunar occultations we can detect errors in the Hipparcos stellar reference frame. By analyzing Baily's beads timing observations of past total and annular solar eclipses using the accurate lunar limb profiles we will be able to detect solar diameter variations.

• 천문학회지
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• 제50권6호
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• pp.191-200
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• 2017

We analyze the time data recorded in Korean astronomical almanacs for the years from 1913 to 1945, which belong to the period in which Japan occupied Korea (1910-1945). These almanacs, published by Japanese scholars, differ from previous almanacs in terms of organization, content, and calendrical methods. In this study, we first extract twelve kinds of time data from the almanacs at the following times: solar terms, rising and setting of the Sun and Moon, transit of the Sun, phases of the Moon (i.e., new Moon, first quarter Moon, full Moon, and last quarter Moon), and eclipses of the Sun and Moon. Then, we compare the time data with that obtained from modern calculations. Even though all time data in the almanacs are tabulated in units of minutes, we calculate the data in units of seconds and determine the root mean square (RMS) deviation values for each kind of time data to estimate the accuracy of the data. Our findings are as follows: First, the kind and tabulation method of time data changes several times. For instance, solar transit time is listed only for six years from 1937 to 1942. Second, the times of two equinoxes and those of a new Moon are considerably close to midnight. Third, there are some typographical errors in the almanacs, particularly in the times of moonrise and moonset. Fourth, the contact times for lunar eclipses represent the times of the umbra and not of the penumbra, which is different from the times for solar eclipses. Finally, the RMS deviation values are approximately 0.5 min on average in all kinds of time data, even though they show slightly large differences in the times related to the Moon. In conclusion, we believe that this study is useful for investigating the time data in the almanacs of other East Asian countries that were published during the same period, such as China, Japan, and Manchuria.

• 천문학회지
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• 제23권2호
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• pp.106-111
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• 1990

Photoelectric observation in 1984 shows light variation outside eclipses. The effect of the changing ambient temperature on the light curves were studied. Difficulty of studying and unitary, or mean, light curve of AR Lac is stressed.