• The Bulletin of The Korean Astronomical Society
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• v.33 no.1
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• pp.65.2-65.2
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• 2008

• The Bulletin of The Korean Astronomical Society
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• v.33 no.2
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• pp.32.1-32.1
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• 2008

• Publications of The Korean Astronomical Society
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• v.30 no.3
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• pp.801-810
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• 2015

The royal astronomical observatory compiled the Astronomical Almanac during the Joseon dynasty, though there were some changes of its organization. However, the observatory underwent sudden changes in the late period mainly due to the influence of historical events such as the Gabo (甲午) and The Eulmi (乙未) Reforms in 1894 and 1895, respectively, and the Japanese invasion in 1910. In this paper, we study the changes of the compilation institution of the Korean Astronomical Almanac and of its organization for the period of 1894 to 1912. During this period, the name of the observatory had been changed several times, from Gwansanggam (觀象監) to Gwansangguk (觀象局) in 1894 and to Gwansangso (觀象所) in 1895. In addition, the affair of the Astronomical Almanac compilation was transferred to the Editorial Bureau [編輯局] of the Ministry of Education [學部] and to the Editing Department [編輯課] of the Governor-General of Korea [朝鮮總督府]. In 1907, the Gwansangso was abolished. Moreover, the affair of timekeeping was separated and the official number of personnel was reduced to less than 5% compared to that of Gwansanggam. Consequently, the royal astronomical observatory was significantly reduced in terms of its functions and the organization through the process of those changes. Therefore, we believe that this period is important when seeking to understand the transition between the traditional Astronomical Almanac of the Joseon dynasty and its modern astronomical counterpart of the present day.

• Journal of The Korean Astronomical Society
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• v.49 no.3
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• pp.93-107
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• 2016

Augmenting the Wide Field Infrared Survey Telescope (WFIRST) microlensing campaigns with intensive observations from a ground-based network of wide-field survey telescopes would have several major advantages. First, it would enable full two-dimensional (2-D) vector microlens parallax measurements for a substantial fraction of low-mass lenses as well as planetary and binary events that show caustic crossing features. For a significant fraction of the free-floating planet (FFP) events and all caustic-crossing planetary/binary events, these 2-D parallax measurements directly lead to complete solutions (mass, distance, transverse velocity) of the lens object (or lens system). For even more events, the complementary ground-based observations will yield 1-D parallax measurements. Together with the 1-D parallaxes from WFIRST alone, they can probe the entire mass range M ≳ M_⊕. For luminous lenses, such 1-D parallax measurements can be promoted to complete solutions (mass, distance, transverse velocity) by high-resolution imaging. This would provide crucial information not only about the hosts of planets and other lenses, but also enable a much more precise Galactic model. Other benefits of such a survey include improved understanding of binaries (particularly with low mass primaries), and sensitivity to distant ice-giant and gas-giant companions of WFIRST lenses that cannot be detected by WFIRST itself due to its restricted observing windows. Existing ground-based microlensing surveys can be employed if WFIRST is pointed at lower-extinction fields than is currently envisaged. This would come at some cost to the event rate. Therefore the benefits of improved characterization of lenses must be weighed against these costs.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.33.2-33.2
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• 2010

We have investigated a relationship among the solar proton events (SPEs), coronal mass ejections (CMEs) and solar flares during the solar cycle 23 (1997-2006). Using 63 SPE dataset, we found that SPE rise time, duration time, and decrease times depend on CME speed and SPE peak intensity depends on the CME earthward direction parameter as well as CME speed and x-ray flare intensity. While inspecting the relation between SPE peak intensity and the CME earthward direction parameter, we found that there are two groups: first group consists of large 6 SPEs (> 10,000 pfu at >10 MeV proton channel of GOES satellite) and shows a very good correlation (cc=0.65) between SPE peak intensity and CME earthward direction parameter. The second group has a relatively weak SPE peak intensity and shows poor correlation between SPE peak intensity and the CME earthward direction parameter (cc=0.01). By investigating characteristics of 6 SPEs in the first group, we found that there are special common conditions of the extremely large proton events (group 1); (1) all the SPEs are associated with very fast halo CME (>1400km/s), (2) they are almost located at disk region, (3) they also accompany large flare (>M7), (4) all they are preceded by another wide CMEs, and (5) they all show helmet streamer nearby the main CME. In this presentation, we will give details of the energy spectra of the 6 SPE events from the ERNE/HED aboard the Solar and Heliospheric Observatory (SOHO), and onset time comparison among the SPE, flare, type II burst, and CME.

• Journal of The Korean Astronomical Society
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• v.33 no.2
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• pp.89-95
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• 2000

As an efficient method to detect blending of general gravitational microlensing events, it is proposed to measure the shift of source star image centroid caused by microlensing. The conventional method to detect blending by this method is measuring the difference between the positions of the source star image point spread function measured on the images taken before and during the event (the PSF centroid shift, ${\delta}{\theta}$c,PSF). In this paper, we investigate the difference between the centroid positions measured on the reference and the subtracted images obtained by using the difference image analysis method (DIA centroid shift, ${\delta}{\theta}$c.DIA), and evaluate its relative usefulness in detecting blending over the conventional method based on ${\delta}{\theta}$c,PSF measurements. From this investigation, we find that the DIA centroid shift of an event is always larger than the PSF centroid shift. We also find that while ${\delta}{\theta}$c,PSF becomes smaller as the event amplification decreases, ${\delta}{\theta}$c.DIA remains constant regardless of the amplification. In addition, while ${\delta}{\theta}$c,DIA linearly increases with the increasing value of the blended light fraction, ${\delta}{\theta}$c,PSF peaks at a certain value of the blended light fraction and then eventually decreases as the fraction further increases. Therefore, measurements of ${\delta}{\theta}$c,DIA instead of ${\delta}{\theta}$c,PSF will be an even more efficient method to detect the blending effect of especially of highly blended events, for which the uncertainties in the determined time scales are high, as well as of low amplification events, for which the current method is highly inefficient.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.49.5-50
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• 2021

We report the optical follow-up observations of three long γ-ray burst events, GRB 201020A, GRB 201103B and GRB 210104A by the network of telescopes in the SomangNet project. We show light curves, color evolution and SED evolution, and fit them to a single power law function to derive decay index and compare their properties with other long GRBs samples. Also, we show a good observational example that 0.4-1m class telescopes in SomangNet have potential to catch dim light from high red shift object (R>22 mag) by deep imaging. In conclusion, we found that three GRBs have optical afterglow properties of long GRB and our results are consistent with the reports of high energy analysis.

• Publications of The Korean Astronomical Society
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• v.38 no.3
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• pp.111-123
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• 2023

In this study, quantitative analysis is attempted on data collected from Chilgapsan Observatory Star Park in Cheongyang-gun, Chungcheongnam-do. The aim of this experimental study in which quantitative analysis of the Astronomical Science Museum in Korea is conducted is to investigate its current situation and secure basic data. As of July 31, 2023, it has had 283,931 cumulative visitors in total. It had the largest number of visitors when it opened (2009 year), after which their number reduced steadily until the pandemic (COVID-19, 2020-2022). Recently, however, the number of visitors has increased. Generally, the number of visitors is highest in August (20.8%) and least in April (4.1%). The visit rate is higher on weekends (Saturday and Sunday) than on weekdays (Monday-Friday), and groups comprise only about 5.3% of the total number of visitors. Moreover, it can be confirmed that the number of visitors increases sharply during events. Finally, it was confirmed that the visit rate was unaffected by weather conditions. Considering these results, we propose the following strategies: 1) Establish a special program that reflects "the weekend effect." 2) Prepare a plan to attract group visitors during the weekdays using "the event effect." 3) Arrange alternative programs (e.g., experiential activities) that can be conducted indoors regardless of weather conditions. We think that our findings will help establish a roadmap for the direction the Astronomical Science Museum should take and aid in preparing a strategic foundation to preemptively respond to unexpected situations (e.g., pandemics).

• Publications of The Korean Astronomical Society
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• v.37 no.3
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• pp.59-79
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• 2022

We investigated the records of astronomical phenomena in the Hyeonjong-Donggung-Ilgi written by the educational office for a crown prince, Sigang-won, during the time of a crown prince of the king Hyeonjong (i.e., from 1649 to 1659). Of the total of 3,625 days, 3,044 astronomical accounts were compiled from astronomical records of 2,003 days. We classified these astronomical accounts into 16 items, grouped into five categories, and statistically analyzed each group. In our analysis, the accounts for atmos-pheric optical phenomena equates to 57.9% of the total, and for celestial phenomena visible during the daytime the percentage is 17.3%. The records related to the approach between two objects such as planets, moon, and stars account for 3.3%, and solar or lunar eclipses take up 0.6%. The ratio of accounts regarding meteor, comet, and fire light (火光) stand at 13.8%, 0.30%, and 6.8%, respectively. Sunny days account for 71.1% of all days per year during this period. We determined that the distribution of the fire light by month is similar to that of the solar halo. We also found that the astronomical records from the Annals of the Joseon Dynasty correspond to only 30% of those of the Hyeonjong-Donggung-Ilgi for the same period. In particular, the phenomena of celestial objects occurring outside the atmosphere are transmitted to the Annals of the Joseon Dynasty in a higher proportion than the phenomena inside the air. It is therefore necessary to use a historical diary like a Donggung-Ilgi to interpret the phenomena in the air such as atmospheric optical events, meteor, and fire light.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.38.1-38.1
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• 2015

Supernova remnants (SNRs) are one of the most energetic astrophysical events and are thought to be the dominant source of Galactic cosmic rays (CRs). A recent report on observations of gamma rays from the vicinity of SNRs have shown strong evidence that Galactic CR protons are accelerated by the shock waves of the SNRs. The actual gamma-ray emission from pion decay should depend on the diffusion of CRs in the interstellar medium. In order to quantitatively analyze the diffusion of high-energy CRs from acceleration sites, we have performed test particle numerical simulations of CR protons using a three-dimensional magnetohydrodynamics (MHD) simulation of an interstellar medium swept-up by a blast wave. We analyse the CRs diffusion at a length scale of order a few pc, and show the Richtmeyer-Meshkov instability can provide enough turbulence downstream of the shock to make the diffusion coefficient close to the Bohm level for energy larger than 30 TeV for a realistic interstellar medium.