• Journal of The Korean Association For Science Education
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• v.33 no.3
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• pp.664-678
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• 2013

This study aims to investigate gifted students' explanations for daily celestial motion from the Earth-based and heliocentric frames of reference. Eleven sixth-grade elementary school students were chosen for this study and data was collected through a questionnaire and an in-depth interview. The collected data was analyzed into celestial objects which are the Sun, the moon and the stars and analyzed based on the Earth-based and heliocentric perspectives again. As a result of the research, most gifted students were able to connect the Earth-based and heliocentric frames of reference with the Sun's daily apparent motion. However, they understood the daily apparent motion of the moon and the stars far less frequently compared to the Sun's motion and could not explain the Earth's rotation clearly. The result of the interview showed that the lack of understanding about the daily celestial motion was caused by inaccurate understanding of the Earth's rotation such as using memorized knowledge learned in school and guessing the answer.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.53.1-53.1
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• 2010

Earth's polar motion has been known for more than one century, and it has been monitored by astrometric observation and recently by space geodetic technique. The Chandler and the annual wobbles are two dominant parts of Earth's polar motion. But according to our recent analysis on a relevant and accurate dataset, another polar motion component, of which period is about 500 days, exists with an amplitude of 20 milliarcseconds in average. This third largest component of polar motion should be caused by resonance of unidentified oscillating mode of Earth, possibly Earth's inner core wobble.

• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.91-96
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• 2016

From the Earth's polar motion time series (IERS 08 C04, since 1981), after removal of seasonal variation by band-pass filtering, we acquired Earth's free Eulerian motion (Chandler wobble) time series. By successive least square error fittings on it, we analyzed amplitude and phase variation of Chandler wobble. We attempted to identify any precursory behavior of the pole before large earthquakes but only to fail. Unlike Smylie's conjecture there was no appreciable motion of the Earth's pole detected at around the each times of recent six largest earthquakes of magnitude over 8.5.

• Journal of the Korean Society of Earth Science Education
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• v.13 no.1
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• pp.29-39
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• 2020

In this study, to find out the learning effects and difficulties of role play activities to learn the earth's rotation and the sun's apparent motion, the degree of concept understanding through role play activities, difficulties arising from activities collected by interview, and eye movement during activities are analyzed. 22 fifth graders participated in this study and collected and analyzed experimental behaviors, post-interviews, and eye movement data during the role play of the students. The study found that students could explain the rotation and direction of the Earth through role play activities, but it was difficult to explain the apparent motion of the sun. Since it is difficult to perceive the sun's apparent motion through role play activities, the learning effect of the earth rotation role play activity is low.

• Journal of Astronomy and Space Sciences
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• v.20 no.4
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• pp.319-326
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• 2003

The motion of each satellite in a tethered satellite system is non-Keplerian in the Earth's gravitational field. In this paper, the tether perturbation force is formulated and compared with the perturbation force due to the Earth's oblateness. Also, the center of mass motion of the tethered satellite system is analyzed. The tether perturbing force on the one of satellites in a tethered satellite system is much bigger than the Earth's oblateness perturbation. The two-body motion approximation of the center of mass is acceptable to describe the motion of the system, when the libration is small.

• Journal of Astronomy and Space Sciences
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• v.30 no.1
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• pp.33-41
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• 2013

Various features of the existing perturbations in the Earth's spin rotation are investigated for the recent and most reliable data by spectral analysis, filtering, and comparison with idealized model. First, theory of Earth's spin rotational perturbation is briefly re-derived in the Earth-fixed coordinate frame. By spectral windowings, different periodic components of the length of day perturbation are separated, and their characters and excitations are discussed. Different periodic components of polar motion are acquired similarly and described with further discussion of their excitations. Causes of the long time trends of both the length of day and polar motion are discussed. Three possible causes are considered for the newly discovered 490-day period component in the polar motion.

• Journal of the Korean Society of Earth Science Education
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• v.13 no.3
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• pp.297-304
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• 2020

This study is to find out experiments of Earth's revolution and which experiment is effective by school level. Researcher investigated and developed eight experiments for students to learn Earth's revolution. Twenty six pre-service teachers did these experiments, discuss about them, chose an effective experiment of Earth's revolution and wrote the reason why. As a result, they thought that an experiment of seasonal constellations is effective for elementary school students, an experiment of seasonal star's spectrum is effective for secondary school students and an experiment of the superior planets' retrograde motion is effective for university students. Pre-service teachers gave reasons such as hands-on experience, connection with textbooks, background knowledge and higher-level thinking.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.6
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• pp.277-283
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• 2020

In order to improve the ground-motion prediction equation, which is an important factor in seismic hazard assessment, it is essential to obtain good quality seismic data for a region. The Korean Peninsula has an environment in which it is difficult to obtain strong ground motion data. However, because digital seismic observation networks have become denser since the mid-2000s and moderate earthquake events such as the Odaesan earthquake (Jan. 20, 2007, M_L 4.8), the 9.12 Gyeongju earthquake (Sep. 12, 2016, M_L 5.8), and the Pohang earthquake (Nov. 15, 2017, M_L 5.4) have occurred, some good empirical data on ground motion could have been accumulated. In this study, we tried to build a ground motion database that can be used for the development of the ground motion attenuation equation by collecting seismic data accumulated since the 2000s. The database was constructed in the form of a flat file with RotD50 peak ground acceleration, 5% damped pseudo-spectral acceleration, and meta information related to hypocenter, path, site, and data processing. The seismic data used were the velocity and accelerogram data for events over M_L 3.0 observed between 2003 and 2019 by the Korean National Seismic Network administered by the Korea Meteorological Administration. The final flat file contains 10,795 ground motion data items for 141 events. Although this study focuses mainly on organizing earthquake ground-motion waveforms and their data processing, it is thought that the study will contribute to reducing uncertainty in evaluating seismic hazard in the Korean Peninsula if detailed information about epicenters and stations is supplemented in the future.

• Journal of Navigation and Port Research
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• v.30 no.9
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• pp.729-734
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• 2006

The authors aim to establish the theory necessary for developing the free gyroscopic compass and focus on mainly two points. One is to suggest north-finding principle by the angular velocity of the earth's rotation, and the other is to suggest orthogonal coordinate transformations of the motion rate of the spin axis, which transforms the components of motion rate in the free gyro frame into those in the platform frame and that this transformed rate is, in turn, transformed into the NED(north-east-down) navigation frame. Subsequently, ship's heading is obtained by using the fore-aft and athwartship components of the motion rate of the spin axis in the NED frame. In addition it was found how to solve the transformation matrix necessary for transforming each frame.

• Journal of Astronomy and Space Sciences
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• v.36 no.1
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• pp.11-20
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• 2019

Being a torque free motion of the rotating Earth, Chandler wobble is the major component in the Earth's polar motion with amplitude about 0.05-0.2 arcsec and period about 430-435 days. Free core nutation, also called nearly diurnal free wobble, exists due to the elliptical core-mantle boundary in the Earth and takes almost the whole part of un-modelled variation of the Earth's pole in the celestial sphere beside precession and nutation. We hereby present a brief summary of their theories and report their recent features acquired from updated datasets (EOP C04 and ECMWF) by using Fourier transform, modelling, and wavelet analysis. Our new findings include (1) period-instability of free core nutation between 420 and 450 days as well as its large amplitude-variation, (2) re-determined Chandler period and its quality factor, (3) fast decrease in Chandler amplitude after 2010.