• Journal of Astronomy and Space Sciences
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• 제14권1호
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• pp.150-157
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• 1997

인공위성의 궤도경사각을 제어하는 남/북 위치보존은 많은 연료를 소모하기 때문에 연료량을 효율적으로 절감할 수 있는 방법의 연구가 중요하다. 이를 위하여 궤도경사각의 변화를 영년항과 주기항으로 나누어 영년변화만을 보정함으로써 기동 연료량을 줄이는 MFT(Minimum Fuel Target)기법을 이용하여 무궁화 위성의 남/북 위치보존을 모의실험하였다. 임무기간(약 10년)동안 모의 실험한 결과를 남/북 위치보존을 위한 다른 두가지 방법인 MCT(Maximum Compensation Target)기법과 TBCT(Track-Back Cho가 Target) 기법으로 구한 연료량과 비교하였다. MFT 기법을 사용할 경우 두 기법에 비해 각각 최소 47일과 15일의 임무기간이 연장되는 것으로 나타났다.

• 천문학논총
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• 제26권3호
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• pp.115-127
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• 2011

Since the thirteenth century, large scale facilities and various instruments for astronomical observation were built and installed in East Asia. During the Yuan Dynasty, S. ti.ntai (Beijing astronomical observatory in the Yuan Dynasty, 司天臺) was built in Beijing in 1279. Various astronomical instruments, including Ganui (Jianyi, simplified armillary sphere, 簡儀), Yang-yi (upward hemisphere, 仰儀) and Gyupyo (gnomon, 圭表) were installed in this observatory. These astronomical instruments were modified and improved by researchers of the Joseon Dynasty. Ganuidae (Joseon astronomical observatory, 簡儀臺) was built in Gyeongbokgung (or Gyeongbok palace, 景福宮), Seoul. Its scale was 31 Cheok (Korean feet in the Joseon Dynasty, 尺) in height, 47 Cheok in length and 32 Cheok in width. Lee, Cheon (李蕆, 1376~1451), a responsible leader of Ganuidae project, set up various astronomical instruments with his colleagues. Ganui and Jeongbangan (direction-determining board, 正方案) were installed at the top of this observatory. Gyupyo was installed at the west side of this observatory and Honui (armillary sphere, 渾儀) and Honsang (celestial globe, 渾象) were installed in a small pavilion which was located next to Gyupyo. A decade after installation, this observatory was moved to the north-west side of the palace but almost destroyed during Japanese invasion of Korea in 1592 except Ganuidae. We have analyzed documents about Ganuidae and investigated Chinese remains of astronomical observatories and artifacts of astronomical instruments. In this paper, we suggest the appearance, structure, arrangement and scale of Ganuidae, which are expected to be used for the restoration of Ganuidae at some day in the near future.

• Journal of Astronomy and Space Sciences
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• 제26권1호
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• pp.9-24
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• 2009

태양주기 23의 태양흑점과 코로나질량방출(Coronal Mass Ejection, CME), 지자기폭풍과의 상호 연관성을 알아보기 위해 CME의 연도별 발생빈도 분포와 북-남 비대칭 분포, 태양흑점수와 면적의 연평균 분포와 북-남 비대칭 분포, 지자기폭풍의 연도별 발생빈도 분포와의 상호 상관관계를 알아보았다. 1996년부터 2007년까지의 SOHO/LASCO 목록 CME의 위치정보를 이용하여 북쪽 반구에서 발생한 CME와 남쪽 반구에서 발생한 CME의 연도별 발생빈도 분포를 알아내었다. 태양흑점수와 면적을 북쪽 반구와 남쪽 반구를 구분하여 그 연평균 분포를 구하였고 지자기 교란정도를 알 수 있는 Ap지수, Dst지수, aa지수를 이용하여 지자기폭풍의 연도별 발생빈도 분포를 구하였다. 이렇게 구한 각각의 분포간의 상호 상관관계를 구하였다. 또한 CME를 각 너비(Angular Width)와 속도(Linear Speed)에 따라 분류하여 흑점 분포, 지자기폭풍의 발생빈도 분포와 상관관계도 알아보았다. 그 결과 CME의 전체 발생빈도는 흑점수와 면적의 전체 분포와의 상관관계가 높았고 흑점수와 면적의 북-남 비대칭 분포와는 상관관계가 낮았다. CME의 북-남 비대칭 분포는 흑점의 북-남 비대칭 분포와 상관관계가 높았다. CME와 지자기폭풍 발생빈도 분포와의 상관관계를 살펴 본 결과 CME 전체나 북-남 비대칭 분포와는 상관도가 낮게 나왔다. 그러나 CME를 규모별로 나누어 그 총 발생빈도와의 상관관계를 알아 본 결과 Ap지수와 aa지수는 속도가 빠른 경우, Dst지수는 각너비나 속도별로 나눈 모든 경우에 상관도가 높게 나왔다. 흑점과 지자기폭풍 발생빈도의 경우 흑점수와 면적의 전체 분포와 지자기폭풍 사이의 상관관계가 높게 나타났다. 이 결과를 통해 CME의 발생빈도 분포는 흑점의 분포와 연관성이 높고 이 둘의 전체 분포와 지자기폭풍의 발생빈도 분포와의 연관성이 높은 것을 알 수 있다. 그리고 CME, 흑점의 북-남 비대칭 분포와 지자기폭풍의 발생빈도 분포의 경우 연관성이 낮은 것을 알 수 있다.

• 천문학회보
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• 제40권2호
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• pp.32.3-33
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• 2015

There exist scaling relations that link the mass of supermassive black holes with both the velocity dispersion and the mass of the central stellar cusp of their host galaxies. This implies that these two components grow in tandem. Feedback from actively accreting supermassive black holes (AGN), in the form of multi-phase gas outflows, has been argued to be the agent of this co-evolution. Here we employ the powerful GMOS integral field spectroscopy unit on the 8.2m Gemini-North telescope to investigate ionized gas outflows of luminous Type 2 AGN in the local Universe (z<0.1). Our sample of 6 galaxies is drawn from the Sloan Digital Sky Survey (SDSS) and was selected based on their [OIII] dust-corrected luminosity (>1042 erg/s) and signatures of outflows in the [OIII] line profile of their spatially integrated SDSS spectra. These are arguably the best candidates to explore AGN feedback in action since they are < 1% of a large local type 2 AGN SDSS sample selected based on their [OIII] kinematics. We combine a careful spectral decomposition of the [OIII] and $H{\alpha}$ line profiles with spatial information on ~0.5kpc scales to understand the outflow kinematics and energetics in these objects. We find clear evidence for strong outflows in [OIII] and occasionally $H{\alpha}$ that are clearly driven by the ionizing radiation of the AGN. We kinematically and spatially decompose outflowing and rotating ionized gas components. We find [OIII] to be a better tracer of AGN outflows, while $H{\alpha}$ appears to be strongly affected by both stellar rotation and outflows induced by ongoing star formation. The observed kinematics and spatial distribution of the ionized gas imply a large opening angle for the outflow. Finally, we find the projected outflow velocity to decrease as a function of distance, while its dispersion shows a more complex structure with a potentially initially increasing trend (out to 0.5-1kpc distances).

• 천문학회보
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• 제36권2호
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• pp.117.1-117.1
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• 2011

We present the smoothness of mid-infrared sky brightness from the Japanese infrared astronomical satellite, AKARI observations. AKARI monitored the north ecliptic pole (NEP) during its cold phase with nine wavebands from 2.4 to 24 ${\mu}m$, out of which six mid-infrared bands are used in this study. Simple sinusoidal fit to the seasonal variation of the sky brightness shows that the mid-infrared brightness towards the NEP is not affected by small-scale features of the interplanetary dust cloud. We applied the power spectrum analysis to the images to search for the fluctuation of sky brightness. The fluctuation powers at 200 arcsecond are estimated to be at most $1.58{\pm}0.33\;nW\;m^{-2}sr^{-1}$ or 0.13% of the total brightness at $7{\mu}m$ and a tleast $0.64{\pm}0.11\;nW\;m^{-2}sr^{-1}$ or 0.02% at $18{\mu}m$. The residual fluctuations at a few arcminute scales at short mid-infrared wavelengths (7, 9, and 11 ${\mu}m$) are consistent with those expected from the diffuse galactic light. At long mid-infrared wavelengths (15, 18, and 24 ${\mu}m$) the measured fluctuations are comparable to or smaller than the one caused by photon noise and their sources are not identified. We conclude that the upper limit of the fluctuation in the zodiacal light is about 0.02% of the sky brightness.

• 천문학회보
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• 제41권1호
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• pp.37.2-37.2
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• 2016

There exist scaling relations that link the mass of supermassive black holes with both the velocity dispersion and the mass of the central stellar cusp of their host galaxies. This implies that galaxies co-evolve with their central black holes, potentially through the feedback from actively accreting supermassive black holes (AGN). We use integral field spectroscopy data from the 8.2m Gemini-North telescope to investigate ionized gas outflows in luminous local (z<0.1) Type 2 AGN. Our sample of 6 galaxies was selected based on their [OIII] dust-corrected luminosity (>$10^{42}erg/s$) and signatures of outflows in the [OIII] line profile of their SDSS spectra. These are arguably the best candidates to explore AGN feedback in action since they are < 1% of a large local type 2 AGN SDSS sample selected based on their [OIII] kinematics. Expanding on previously reported results concerning the kinematic decomposition and size determination of these outflows, here we report their photoionization properties and energetics. We find strong evidence that connect the extreme kinematics of the ionized gas with AGN photoionization. The kinematic component related to the AGN-driven outflow is clearly separated from other kinematic components, such as gravitation- or stellar-driven motions, on the velocity and velocity dispersion diagram. Our spatially resolved kinematic analysis reveals that up to 90% of the mass and kinetic energy of the outflow is contained within the central kiloparcec of the galaxy. The total mass and kinetic energy of the outflow correlate well with the AGN bolometric luminosity, resulting in energy conversion efficiencies between 0.01% and 1%. Intriguingly, we detect ubiquitous signs of ongoing circumnuclear star formation. Their small size, the centrally contained mass and energy, and the universally detected circumnuclear star formation cast doubts on the potency of these AGN-driven outflows as agents of negative feedback.

• 천문학논총
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• 제39권1호
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• pp.1-12
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• 2024

In this study, we investigated the time signal devices of Deungnu (circa 1270) and Gungnu (1354), the water clocks produced during the Yuan Dynasty (1271-1368). These clocks influenced Heumgyeonggaknu (1438) of the Joseon Dynasty (1392-1910), exemplifying the automatic water clocks of the Yuan Dynasty. Deungnu, Gungnu, and Heumgyeonggaknu can be considered as automatic mechanical clocks capable of performances. The Jega-Yeoksang-Jip (Collection of Calendrical and Astronomical Theories of Various Chinese Masters) contains records of Deungnu extracted from the History of the Yuan Dynasty. We interpreted these records and analyzed reproduction models and technical data previously produced in China. The time signal device of Deungnu featured a four-story structure, with the top floor displaying the four divine constellations, the third floor showcasing models of these divinities, the second floor holding 12-h jacks and a 100-Mark ring, and the first floor with four musicians and a 100-Mark Time-Signal Puppet providing a variety of visual attractions. We developed a 3D model of Deungnu, proposing two possible mechanical devices to ensure that the Time-Signal Puppet simultaneously pointed to the 100-Mark graduations in the east, west, south, and north windows: one model reduced the rotation ratio of the 100-Mark ring to 1/4, whereas the other model maintained the rotation ratio using four separate 100-Mark rings. The power system of Deungnu was influenced by Suunuisangdae (the water-driven astronomical clock tower) of the Northern Song Dynasty (960-1127); this method was also applied to Heumgyeonggaknu in the Joseon Dynasty. In conclusion, these automatic water clocks of East Asia from the 13th to 15th centuries symbolized creativity and excellence, representing scientific devices that were the epitome of clock-making technology in their times.

• Journal of Astronomy and Space Sciences
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• 제30권4호
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• pp.315-320
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• 2013

Space geodetic techniques can be used to obtain precise shape and rotation information of the Earth. To achieve this, the representative combination solution of each space geodetic technique has to be produced, and then those solutions need to be combined. In this study, the representative combination solution of very long baseline interferometry (VLBI), which is one of the space geodetic techniques, was produced, and the variations in the position coordinate of each station during 7 years were analyzed. Products from five analysis centers of the International VLBI Service for Geodesy and Astrometry (IVS) were used as the input data, and Bernese 5.0, which is the global navigation satellite system (GNSS) data processing software, was used. The analysis of the coordinate time series for the 43 VLBI stations indicated that the latitude component error was about 15.6 mm, the longitude component error was about 37.7 mm, and the height component error was about 30.9 mm, with respect to the reference frame, International Terrestrial Reference Frame 2008 (ITRF2008). The velocity vector of the 42 stations excluding the YEBES station showed a magnitude difference of 7.3 mm/yr (30.2%) and a direction difference of $13.8^{\circ}$ (3.8%), with respect to ITRF2008. Among these, the 10 stations in Europe showed a magnitude difference of 7.8 mm/yr (30.3%) and a direction difference of $3.7^{\circ}$ (1.0%), while the 14 stations in North America showed a magnitude difference of 2.7 mm/yr (15.8%) and a direction difference of $10.3^{\circ}$ (2.9%).

• 지구물리
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• 제3권3호
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• pp.153-160
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• 2000

동아시아 지역에 있는 8개 IGS GPS상시관측소의 관측자료를 이용하여 한반도 주변의 지각운동 속도를 재고 그 결과를 분석하였다. 이를 위해 1995년 5월부터 1997년 12월까지 약 32개월간의 7일 간격 GPS자료를 Bernese 4.0으로 처리하여 하루에 한번씩 대전을 기준한 각 지점의 좌표를 측정하였다. 측정된 좌표의 시간에 따른 선형회기분석을 통해 각 지점의 성분별 연간 지각운동 속도를 결정하였다. 그 결과, 총 32개월 데이터를 사용한 4지점(쓰구바, 우수다, 타이완, 상하이)에 대해서는 1 mm/year 이하의 표준오차로 평면성분의 연간 지각운동 속도를 결정할 수 있었다. 이 연구로 측정된 유라시아판 안쪽에 위치한 5지점의 속도는 각 지점마다 약간의 차이가 있으나 대전에 대해 1 cm/year 이하의 상대 속도를 보인 반면, 일본의 2지점의 속도는 유라시아판 내부의 6지점들과 전혀 다른 경향을 나타냈다. 이것은 두 지점이 태평양판, 유라시아판, 북아메리카판, 필리핀판의 경계부에 놓여 있어 이들 4판의 상호작용을 받기 때문이라 판단된다. 한국과 일본이 매년 약 3cm씩 접근하고 있다는 사실을 이 연구를 통해 확인할 수 있었다.

• 자원환경지질
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• 제48권5호
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• pp.391-400
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• 2015

남한은 철강의 수요나 생산에 비해 그 원료가 되는 철광석의 생산이 미약한 반면, 북한은 상당한 철 매장량을 보유하고 있으나 자원량에 비해 생산량이 극히 미진하다. 또한 북한의 폐쇄성으로 인해 북한의 자원에 대한 정보가 미비하고, 그 신뢰성에 의문이 있다. 본 연구는 북한의 철광산 중 세계적인 노천광산으로 알려진 무산광산을 대상으로, Landsat MSS, ASTER 위성영상자료와 수치지형도를 통해 1976~2007년 사이의 자원량과 생산량을 추정하였다. 원격탐사를 통해 산정한 무산광산의 넓이는 1976년을 기준으로 총 약 $6.1km^2$의 면적이 증가하였으며, 광산 내 채광지의 크기는 지도대수기법을 통해 $4.9km^2$로 산정되었다. 또한, 산정된 채광지 내 약 3.2억 $m^3$의 체적을 3차원 모델링을 이용하여 산출한 후, 무산광산과 동일한 암상으로 간주되는 중국 안산층의 철광석 평균밀도와 연산하여 약 7.3억 톤의 자원량과 약 2.4억 톤의 생산량을 추정하였다. 이 수치는 연 평균 810만 톤 수준의 생산량으로, 기존에 보고된 수치와 비교하였을 때, 상당한 일치성을 보였다. 본 연구는 남북자원교류사업을 위한 기초자료로써 유용하게 이용될 수 있을 것으로 기대된다.