• 천문학회보
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• 제37권1호
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• pp.90.2-90.2
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report the results of our investigations on the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropout events and discuss implications on the effects of the drift loss on the flux levels at inner L regions.

• 천문학회보
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• 제37권2호
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• pp.122-122
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report some case studies showing energy dependence during magnetopause shadowing effect.

• 천문학회보
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• 제44권1호
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• pp.39.1-39.1
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• 2019

Not all stars in the Universe are gravitationally bounded to galaxies. Since first discovered in 1951, observations have revealed that a significant fraction of stars fills the space between galaxies in local (low-redshift) galaxy clusters, observed as diffuse intracluster light (ICL). Theoretical models provide mechanisms for the production of intracluster stars as tidally stripped material or debris generated through numerous galaxy interactions during the hierarchical growth of the galaxy cluster. These mechanisms predict that most intracluster stars in local galaxy clusters are long-accumulated material since z~1. However, there is no observational evidence to verify this prediction. Here we report observations of abundant ICL for a massive (above $10^{14}$ solar masses) galaxy cluster at a redshift of z=1.24, when the Universe was 5 billion years old. We found that more than 10 per cent of the total light of the cluster is contributed by the diffuse ICL out to 110 kpc from the center of the cluster, comparable to 5-20 per cent in local, massive galaxy cluster. Furthermore, we found that the colour of the brightest cluster galaxy located in the core of the cluster is consistent with that of the ICL out to 200 kpc. Our results demonstrate that the majority of the intracluster stars present in the local Universe, contrary to most previous theoretical and observational studies, were built up during a short period and early (z>1) in the history of the Virgo-like massive galaxy cluster formation, and might be concurrent with the formation of the brightest cluster galaxy.

• 천문학회보
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• 제39권2호
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• pp.96.1-96.1
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• 2014

The rotation of asteroids can help reveal not only the fundamental characteristics of asteroids but also the origin and evolution of our Solar System. From the photometric observations for NEA 162173 (1999 JU3) and Maria family asteroids using 0.5 m- to 2 m- class telescopes at 10 observatories in the northern hemisphere, I obtained a total of 260 lightcurves for 97 asteroids and derived synodic rotational periods for 51 objects, including newly obtained periods of 34 asteroids. For the sake of efficiency, I developed an observation scheduler, SMART (Scheduler for Measuring Asteroid RoTation) and a photometric analysis software subsystem, ASAP (Asteroid Spin Analysis Package). Based on the lightcurve analysis of NEA 162173 (1999 JU3) and Maria family asteroids, 1) I present the rotational and observational characteristics of 1999 JU3 and provided the Hayabusa-2 Science team with the information on pole orientations, 2) I investigated correlations among rotational periods, amplitudes of lightcurves, and sizes, and conclude that the rotational properties of old-type family asteroids have been changed considerably by the YORP effect. 3) Finally, I found the Yarkovsky footprints on the Maria asteroid family and estimated that approximately 37 to 75 Maria family asteroids larger than 1 km have entered the near-Earth space every 100 Myr. This study should reveal the collisional history and transport route of the members from the resonance region to the near Earth space, for the first time.

• 천문학회지
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• 제56권1호
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• pp.75-89
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• 2023

We investigate the astronomical phenomenon records of Sukjong's Chunbang-Ilgi made by Sigangwon (Royal Educational Office of the Crown Prince) at which King Sukjong was the crown prince (i.e., 1667 January 24-1674 September 22). From the daily records of 2,799 days, we extract the astronomical records of 1,443 days and classify them into 14 categories. Then, we group the records of each category into five phenomena (Atmosphere, Eclipse, Daylight Appearance, Apparition, and Appulse) and compare them with the results of modern astronomical computations wherever possible. Except for Atmosphere group comprising records of meteorological events, such as solar halo, lunar halo, and unusual clouds, the significant findings in every other group are as follows: In Eclipse group, the solar eclipse that occurred on 1673 August 12 was unobservable in Korea, which is in contrast to the record of Joseonwangjo-Sillok (Annals of the Joseon Dynasty), which states that the sun was in eclipse around sunset time, as observed at Nam mountain. From the lunar eclipse records, we verify that the Joseon court did not change the date of the events observed after midnight. In Daylight Appearance group, we confirm that this phenomenon was observed during the daytime and not during twilight. We further suggest that if observation conditions are met, a celestial body brighter than -2.3 mag could be seen during the daytime with the naked-eye. In Apparition group, we find the possibilities that the Orionid meteor shower had influence on the meteor records and the seasonality on the aurora records. We also find that the Korean records in which the coma of comet C/1668 E1 was located below the horizon were overlooked in previous studies. Finally, we find that the records of Appulse group generally agree with the results of modern calculations. The records of Beom (trespass in literal) and Sik (eating in literal) events show average angular separations of 1.2° and 1.0°, respectively. In conclusion, we believe this work helps study the astronomical records of other logs of Sigangwon, such as Sukjong's Chunbang-Ilgi.

• 한국철학논집
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• 제39호
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• pp.53-83
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• 2013

이 글은 황윤석(1729-1791)을 사례로 삼아 18세기 조선 지식인들에게서 천인관계 문제가 어떻게 변화해 가고 있었는가를 검토하는 데 목표를 둔다. 천인관계 문제는 유학의 변화를 가늠하는 중요한 지표로서, 전통적으로 유학사의 핵심 주제 가운데 하나로 자리 잡아왔다. 황윤석은 주자학의 바탕 위에서 서학(Western Learning)을 수용한 인물이라는 점에서 이 문제를 검토하기 위한 좋은 사례의 하나이다. 황윤석의 학문은 주자학의 범위를 거의 벗어나지 않았지만, 어려서부터 고학(古學)에 심취했고, 이를 바탕으로 서학(西學)에 관심을 가졌다. 이수(理數)는 고학과 서학을 관통하는 핵심 개념으로서, 종래의 선험적이고 신비적인 진리에서 부분적이나마 경험적이고 실용적인 지식을 함축하는 개념으로 확장되었다. 황윤석은 천문 현상에 대한 이해에서 사실중심적 접근법과 가치중심적 접근법을 병행하였다. 서양 천문학은 그로 하여금 사실중심적 접근법의 측면에서 많은 진전을 이루도록 해 주었지만, 그럼에도 불구하고 그는 가치중심적 접근법을 통해 일 월식을 비롯한 천문의 변리(變異)에 대해 재리논적(災異論的) 관점을 유지할 수 있었다. 사실 가치의 이분법은 당시 주자학이 새로운 지식의 유입에 맞서 스스로의 정체성을 고수하기 위한 방법의 하나였다고 할 수 있다. 그것은 '천도(자연) 인사(인간)' 방향의 간섭을 배제하는 것일 뿐, '인사(인간) 천도(자연)' 방향의 관심까지 부정하는 것은 아니었다. 자연의 감계적 기능을 긍정적으로 강조하는 그가 보기에 천인관계론은 여전히 중요한 논제였다.

• Journal of Astronomy and Space Sciences
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• 제38권3호
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• pp.175-183
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• 2021

The dependencies of the chemical element abundances in stellar atmospheres with respect to solar abundances on the second ionization potentials of the same elements were investigated using the published stellar abundance patterns for 1,149 G and K giants in the Local Region of the Galaxy. The correlations between the relative abundances of chemical elements and their second ionization potentials were calculated for groups of stars with effective temperatures between 3,764 and 7,725 K. Correlations were identified for chemical elements with second ionization potentials of 12.5 eV to 20 eV and for elements with second ionization potentials higher than 20 eV. For the first group of elements, the correlation coefficients were positive for stars with effective temperatures lower than 5,300 K and negative for stars with effective temperatures from 5,300 K to 7,725 K. The results of this study and the comparison with earlier results for hotter stars confirm the variations in these correlations with the effective temperature. A possible explanation for the observed effects is the accretion of hydrogen and helium atoms from the interstellar medium.

• 천문학논총
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• 제28권2호
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• pp.25-36
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• 2013

Chumsungdae is an ancient astronomical observatory whose main role was doing 'chunmoon'. It was administrate by a royal advisory agency on state affairs. The observers observed the heaven on the observatory platform, recorded peculiar events, and watched and interpreted the signs displayed in the heaven. Chumsungdae is an stonemasonry which represents almanac principles with its peculiar shapes and the numbers of strata and stones. The numbers were thoroughly invented to match exactly the almanac constants. Chumsungdae is comprised largely of three main parts, namely the square base, the stratified cylindrical body, and the top #-shaped stonework, and the total number of stones is 404. The number of the strata (27) and the height of the cylindrical body (27 尺) stand for the days in a sidereal month (27.3 days), which implies that the motion of the Moon with respect to the stars was given more priority than to the Sun at that time of geocentricism. And the cylindrical body was thoroughly designed to consist of 365 stones, which is of course the number of days in a solar year. In addition, there are 12 strata each under and above the south entrance and this in sum makes the 24 divisions of the year. Also there is 182 stones below the 13th stratum and this represents the number of days in the winter ~ summer solstice period, and the rest 183 stones the vice versa. The #-shaped top stonework was aligned in such a way that one of the diagonals points the direction of sunrise on the winter solstice. The square base also layed with the same manner. The south entrance was built 16 degrees SE, and the upright direction of the right pillar stone coincides with the meridian circle. This was a kind of built-in standard meridian circle facilitating the observations. In a symbolic sense, Chumsungdae was thought as the tunnel reaching the heaven, where the observers wished to be enlightened with the signs and inspirations in need. With the craftsmanship and skill, the builder reinforced the stratified cylindrical body with two sets of #-shaped beam stones, piercing at a right angle at 19th ~ 20th and 25th ~ 26th strata. Likewise, by placing the double #-shaped stonework with 8 beam stones on the platform of the observatory, both the stability of the stonemasonry and a guard rail for the nightly observers were securely provided.