• 천문학논총
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• 제38권1호
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• pp.1-12
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• 2023

Numerous Sundials were fabricated during the reign of King Sejong of the Joseon Dynasty. One among them is Jeongnam-Ilgu (the Fixing-South Sundial), where the time can be measured after setting up the suitable meridian line without a compass. We reconstructed the new Jeongnam-Ilgu model based on the records of 'Description of Making the Royal Observatory Ganui (簡儀臺記)' in the Veritable Record of King Sejong. Jeongnam-Ilgu has a summer solstice half-ring under a horizontal ring which is fixed to two pillars in the north and south, and in which a declination ring rotates around the polar axis. In our model, the polar axis matches the altitude of Hanyang (that is Seoul). There are two merits if the model is designed to install the polar axis in the way that enters both the north and south poles and rotates in them: One is that it is possible to fix the polar axis to the declination ring together with the cross-strut. The other is that a twig for hanging weights can be protruded on the North Pole. The declination ring is supposed to be 178 mm in diameter and is carved on the scale of the celestial-circumference degrees on the ring's surface, where a degree scale can be divided into four equal parts through the diagonal lines. In addition, the time's graduation that is drawn on the summer solstice half-ring makes it possible to measure the daytime throughout the year. An observational property of Jeongnam-Ilgu is that a solar image can be obtained using a pin-hole. The position cast by the solar image between hour circles makes a time measurement. We hope our study will contribute to the restoration of Jeongnam-Ilgu.

• Journal of Astronomy and Space Sciences
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• 제34권1호
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• pp.67-73
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• 2017

In this paper, we investigate the observations of Venus in daytime that are recorded in the Goryeosa (History of the Goryeo Dynasty, A.D. 918-1392). There are a total of 167 accounts of such observations in this historical book, spanning a period of 378 yr (from 1014 to 1392). These include six accounts where the days of the observation are not specified and two accounts where the phase angles are outside the calculation range of the equation used in our study. We analyze the number distribution of 164 accounts in 16 yr intervals covering the period from 1023 to 1391. We find that this distribution shows its minimum at around 1232, when the Goryeo dynasty moved the capital to the Ganghwa Island because of the Mongol invasion, and its maximum at around 1390, about the time when the dynasty fell. In addition, we calculate the azimuth, altitude, solar elongation, and apparent magnitude of Venus at sunset for 159 observations, excluding the eight accounts mentioned above, using the DE 406 ephemeris and modern astronomical algorithms. We find that the average elongation and magnitude of Venus on the days of those accounts were ${\sim}40^{\circ}$ and -4.5, respectively, whereas the minimum magnitude was -3.8. The results of this study are useful for estimating the practical conditions for observing Venus in daylight with the naked eye and they also provide additional insight into the corresponding historical accounts contained in the Goryeosa.

• 천문학회보
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• 제46권2호
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• pp.57.4-58
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• 2021

Asteroids have undergone various processes such as impacts, space weathering, and thermal evolution. Because they expose their surfaces to space without atmosphere, these evolutional processes have been recorded directly on their surfaces. The remote-sensing observations have been conducted to reveal these evolutional histories of the target asteroids. For example, crater and boulder distributions are unambiguous evidence for past nondestructive impacts with other celestial bodies. Multiband and spectroscopic observations have revealed space-weathering history (as well as compositions). Whereas most physical quantities have been examined intensively using spacecraft and telescopes, only a little has been studied on "the grain size". It is one of the fundamental physical quantities for diagnosing the collisional and thermal history of asteroids. Our group has conducted polarimetric research of asteroids (as well as Moon [1]) to determine the particle size and further investigate the evolutional histories of target asteroids [2],[3]. For example, the existence of regolith on an S-type asteroid, Toutatis, was suggested almost twenty years before space exploration [4]. Moreover, we reported that near-Sun asteroids indicate a signature of submillimeter grains, which could be created by a thermal sintering process by solar radiation [5]. However, it is important to note that in-situ polarimetry has not been reported on the asteroid surface, although the Korean Lunar Exploration Program aims to do polarimetry on the lunar surface [6]. Therefore, it is expected that the polarizer mounted on the Korean Apophis spacecraft can make the first estimate of the grain size and its regional variation over the Apophis surface. In this presentation, we outline research of S-type asteroid surfaces through remote-sensing observations and consider the role of polarimetry. Based on this review, we consider the purpose, potentiality, and strategy of the polarimetry using the onboard device for the Apophis spacecraft. We will report a possible polarization phase curve of Apophis estimated from ordinary chondrites and past observational data of S-type asteroids, taking account of the space weathering effect. Based on this estimation, we will consider the strategy of how to determine the particle size (and space weathering degree) of the Apophis surface. We will also mention the detectability of dust hovering on the surface.

• 우주기술과 응용
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• 제3권1호
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• pp.1-25
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• 2023

In this paper, I briefly introduce recently terminated, current, and future scientific spacecraft missions for in situ and remote-sensing observations of Earth's and other planetary magnetospheres as of February 2023. The spacecraft introduced here are Geotail, Cluster, Time History of Events and Macroscale Interactions during Substorms / Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (THEMIS / ARTEMIS), Magnetospheric Multiscale (MMS), Exploration of energization and Radiation in Geospace (ERG), Cusp Plasma Imaging Detector (CuPID), and EQUilibriUm Lunar-Earth point 6U Spacecraft (EQUULEUS) for recently terminated or currently operated missions for Earth's magnetosphere; Lunar Environment Heliospheric X-ray Imager (LEXI), Gateway, Solar wind Magneto-sphere Ionosphere Link Explorer (SMILE), HelioSwarm, Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM), Geostationary Transfer Orbit Satellite (GTOSat), GEOspace X-ray imager (GEO-X), Plasma Observatory, Magnetospheric Constellation (MagCon), self-Adaptive Magnetic reconnection Explorer (AME), and COnstellation of Radiation BElt Survey (CORBES) approved for launch or proposed for future missions for Earth's magnetosphere; BepiColombo for Mercury and Juno for Jupiter for current missions for planetary magnetospheres; Jupiter Icy Moons Explorer (JUICE) and Europa Clipper for Jupiter, Uranus Orbiter and Probe (UOP) for Uranus, and Neptune Odyssey for Neptune approved for launch or proposed for future missions for planetary magnetospheres. I discuss the recent trend and future direction of spacecraft missions as well as remaining challenges in magnetospheric research. I hope this paper will be a handy guide to the current status and trend of magnetospheric missions.

• 천문학논총
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• 제36권3호
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• pp.79-95
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• 2021

This study aims to develop a restoration model of an armillary sphere of Tongcheon-ui (Pan-celestial Armillary Sphere) by referring to the records of Damheonseo (Hong Dae-Yong Anthology) and the artifact of an armillary sphere in the Korean Christian Museum of Soongsil University. Between 1760 and 1762, Hong, Dae-Yong (1731-1783) built Tongcheon-ui, with Na, Kyung-Jeok (1690-1762) designing the basic structure and Ann, Cheo-In (1710-1787) completing the assembly. The model in this study is a spherical body with a diameter of 510 mm. Tongcheon-ui operates the armillary sphere by transmitting the rotational power from the lantern clock. The armillary sphere is constructed in the fashion of a two-layer sphere: the outer one is Yukhab-ui that is fixed; and the inner one, Samsin-ui, is rotated around the polar axis. In the equatorial ring possessed by Samsin-ui, an ecliptic ring and a lunar-path ring are successively fixed and are tilted by 23.5° and 28.5° over the equatorial ring, respectively. A solar miniature attached to a 365-toothed inner gear on the ecliptic ring reproduces the annual motion of the Sun. A lunar miniature installed on a 114-toothed inner gear of the lunar-path ring can also replay the moon's orbital motion and phase change. By the set of 'a ratchet gear, a shaft and a spur gear' installed in the solstice-colure double-ring, the inner gears in the ecliptic ring and lunar-path ring can be rotated in the opposite direction to the rotation of Samsin-ui and then the solar and lunar miniatures can simulate their revolution over the period of a year and a month, respectively. In order to indicate the change of the moon phases, 27 pins were arranged in a uniform circle around the lunar-path ring, and the 29-toothed wheel is fixed under the solar miniature. At the center of the armillary sphere, an earth plate representing a world map is fixed horizontally. Tongcheon-ui is the armillary sphere clock developed by Confucian scholars in the late Joseon Dynasty, and the technical level at which astronomical clocks could be produced at the time is of a high standard.

• 천문학논총
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• 제39권1호
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• pp.13-26
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• 2024

The armillary sphere, an astronomical observation device embodying the Orbital Heaven Theory of the Later Han Dynasty in China, holds both historical and scientific significance. It has been produced in various forms by many individuals since its inception in the era of King Sejong in the Joseon Dynasty. A prominent figure in this field was Nam Byeong-cheol (南秉哲, 1817-1863), known for his work 'Uigijipseol' (儀器輯說), published in 1859, which detailed the history, production methods, and usage of the armillary sphere. This text particularly highlights 21 applications of the armillary sphere, divided into 33 measurements, covering aspects like installation, time, and positional measurements, supplemented with explanations of spherical trigonometry. Despite numerous records of the armillary sphere's design during the Joseon Dynasty, detailed usage information remains scarce. In this study, the 33 measurements described in 'Uigijipseol' (儀器輯說) were systematically classified into six for installation, nineteen for position measurement, seven for time measurement, and one for other purposes. Additionally, the measurement methods were analyzed and organized by dividing them into the ecliptic ring, moving equatorial ring, and fixed equatorial ring of the armillary sphere. In other words, from a modern astronomical perspective, the results of schematization for each step were presented by analyzing it from the viewpoint of longitude, right ascension, and solar time. Through the analysis of Nam's armillary sphere, this study not only aims to validate the restoration model of the armillary sphere but also suggests the potential for its use in basic astronomical education based on the understanding of the 19th-century Joseon armillary sphere.

• Journal of Astronomy and Space Sciences
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• 제40권1호
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• pp.29-33
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• 2023

An unexplained acceleration on the order of 10^-8 cm s^-2, which is close to cH, where c is the speed of light and H is the Hubble constant, is detected in gravitationally bound systems of different scales, from the solar system to clusters of galaxies. We found that any test body located inside a fractal structure with fractal dimension D = 2 experiences acceleration of the same order and confirmed the previous work that photons propagating through this structure decrease the frequency owing to gravitational redshift. The acceleration can be directed against the movement of the test body. The fractal distribution of the matter should be at scales of at least hundreds of megaparsecs to a few gigaparsecs for the existence of this acceleration.

• 천문학회보
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• 제46권2호
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• pp.35.5-36
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• 2021

'역상고성'은 '신법산서'에 수록되어 있는 티코브라헤의 역법체계와 그 밖의 천문 내용들을 중국인 천문학자들에 의하여 확실하게 정리를 하였지만 '역상고성'에 따른 추보는 천상과 불일치를 보게 되었다. 藪內淸(야부우치 키요시) 저(1969), 유경로 역(1985)에 의하면 이러한 불일치는 옹정 8년 6월 초 1일의 일식이었는데 예보의 오류를 정정한다는 것을 중국 천문학자들이 감당하기 어려웠다. 퀘글러(Ignatius Kögler, 戴進賢, 1680~1746)와 페레이라(Andreas Pereira, 서무덕(徐懋德), 1690-1743) 등의 선교사 천문학자들이 칙명을 받아 종사하게 되고, 이들이 중심이 되어 '역상고성'보다 더 진보된 서양천문 역법에 기초를 둔 역서가 편찬되게 되었다. '신법산서'와 '역상고성'은 모델에서는 평원(平圓)을 사용하지만 '역상고성후편'에서는 타원(楕圓) 모델을 사용하게 된다. 건륭 7년(1742년)에 10권이 완성되어 '역상고성후편'이라 명하였다. 타원모델을 채택하였지만 지동설에 대한 내용은 전혀 기술되어 있지 않다. 아마도 태양이나 달의 운동을 추보하는데 지구를 중심으로 해야 하기에 이에 대한 언급을 필요치 않았을 수도 있다. '역상고성후편' 은 태양과 달의 운행, 일식과 월식에 대해서만 다루고 있다.그러나 '역상고성'에서는 청몽기차나 지반경차를 티코브라헤의 표 값을 그대로 사용하였고, 이 값들이 관측과 관련이 되어 있음을 설명하려는 무리를 두고 있다. 너무 정확하게 값들이 관측 값들로부터 유도되어 의심이 갈 정도이다. 카시니(Giovanni Domenico Cassini, 喝西尼, 1625~1712)는 자신의 동료 리셰와 함께 파리와 프랑스령 기아나 카이엔에서 충의 위치에 있는 화성과 부근 별의 고도를 관측하여 충의 위치에 있는 화성의 시차를 측정하여 최초로 태양과 지구 사이의 거리를 어림하고, 태양의 지반 경차를 현재와 값과 거의 비슷하게 얻었다. '역상고성후편'에서는 이 내용을 상세하게 다루고 있다. 또한 대기에서 입사각과 굴절각 사이에 Snell의 법칙이 성립하는데 이를 이용하여 모호하게 알았던 청몽기차를 대기의 굴절을 이용하여 현재의 값과 비슷한 값을 얻어 사용할 수 있게 되었다. 이는 모든 천체의 위치를 관측하는데 있어서 매우 정확한 값들을 얻을 수 있게 되고 이에 따라 황도-적도 경사각도 정확하게 얻어진다. '역상고성후편'은 옹정원년을 역원으로 하고 있다. 태양의 운행에 있어서 케플러의 타원 궤도를 이용하게 된다. '신법산서'와 '역상고성'에서는 평균근점이각 M을 모델에서 보여 줄 수 있지만 타원 궤도에서는 이 각이 면적각으로 주어지고, 원 대신 타원을 다루기에 쉽지 않다. 현재는 케플러 방정식을 풀어 가감차를 구하게 되는데 이를 기하학적으로 풀이하는 차적구적법을 소개하고 있다. 이와 함께 면적을 이용하여 타원계각과 타원차각을 구하는 차각구각법도 소개한다. 타원계각과 타원차각을 모두 고려하였기에 현재의 태양의 운동을 기술하는 타원모델과 완벽하게 같다. 다만 사용하는 상수가 아주 조금 다를 분이다. 태양의 경도를 추보하는 방법도 동지점을 기준으로 하고 현재의 방법과 동일하다. 달의 운행도 타원 궤도를 사용한다. '역상고성후편'의 내용은 우리나라의 전해져서 1860년 남병길이 쓴 '시헌기요(時憲紀要)'에는 태양, 달, 일·월식, 오행성의 운동, 항성의 위치, 시간 등을 추보하는데 필요한 내용들이 매뉴얼화 되어 기록되어 있고, 1862년 남병철이 쓴 '추보속해(推步續解)'에도 같은 내용을 담고 있다.

• 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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• 제56권2호
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• pp.213-224
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• 2023

Type II solar radio bursts show frequency drifts from high to low over time. They have been known as a signature of coronal shock associated with Coronal Mass Ejections (CMEs) and/or flares, which cause an abrupt change in the space environment near the Earth (space weather). Therefore, early detection of type II bursts is important for forecasting of space weather. In this study, we develop a deep-learning (DL) model for the automatic detection of type II bursts. For this purpose, we adopted a 1-D Convolution Neutral Network (CNN) as it is well-suited for processing spatiotemporal information within the applied data set. We utilized a total of 286 radio burst spectrum images obtained by Hiraiso Radio Spectrograph (HiRAS) from 1991 and 2012, along with 231 spectrum images without the bursts from 2009 to 2015, to recognizes type II bursts. The burst types were labeled manually according to their spectra features in an answer table. Subsequently, we applied the 1-D CNN technique to the spectrum images using two filter windows with different size along time axis. To develop the DL model, we randomly selected 412 spectrum images (80%) for training and validation. The train history shows that both train and validation losses drop rapidly, while train and validation accuracies increased within approximately 100 epoches. For evaluation of the model's performance, we used 105 test images (20%) and employed a contingence table. It is found that false alarm ratio (FAR) and critical success index (CSI) were 0.14 and 0.83, respectively. Furthermore, we confirmed above result by adopting five-fold cross-validation method, in which we re-sampled five groups randomly. The estimated mean FAR and CSI of the five groups were 0.05 and 0.87, respectively. For experimental purposes, we applied our proposed model to 85 HiRAS type II radio bursts listed in the NGDC catalogue from 2009 to 2016 and 184 quiet (no bursts) spectrum images before and after the type II bursts. As a result, our model successfully detected 79 events (93%) of type II events. This results demonstrates, for the first time, that the 1-D CNN algorithm is useful for detecting type II bursts.