• Journal of the Korean earth science society
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• 제31권7호
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• pp.827-838
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• 2010

The purpose of this study is to identify the conceptions of elementary school teachers regarding the variation scale about astronomical distance and its accuracy with distance increased. The astronomical distance questionnaire was administered to 69 elementary school teachers, then; three teachers were selected to interview about their conceptions. Results showed that many elementary school teachers overestimated the distance from the Earth to the Moon and to the Sun, and dramatically underestimated the distances to the nearest star and to the nearest galaxy. They inferred astronomical distance with the use of both intuitive (psychological) measure and theoretical (calculative) measure. They well recited the terminology such as AU and a light-year, yet they did not show a good understanding of what the terms exactly means. Some teachers thought that the distance to Neptune is farther than the distance from Earth to the nearest star. There was a considerable variability in the participants' estimates of astronomical distances. Elementary school teachers showed a tendency to overestimate the distance as it gradually increases to the outer solar system.

• Publications of The Korean Astronomical Society
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• 제30권2호
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• pp.121-123
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• 2015

We report our measurements of the trigonometric distance and proper motion of IRAS 20056+3350, obtained from the annual parallax of $H_2O$ masers. Our distance of $D=4.69^{+0.65}_{-0.51}kpc$, which is 2.8 times larger than the near kinematic distance adopted in the literature, places IRAS 20056+3350 at the leading tip of the Local arm and proximal to the Solar circle. We estimated the proper motion of IRAS 20056+3350 to be (${\mu}_{\alpha}cos{\delta}$, ${\mu}_{\delta}$) = ($-2.62{\pm}0.33$, $-5.65{\pm}0.52$) $mas\;yr^{-1}$ from the group motion of $H_2O$ masers, and use our results to estimate the angular velocity of Galactic rotation at the Galactocentric distance of the Sun, ${\Omega}_0=29.75{\pm}2.29km\;s^{-1}kpc^{-1}$, which is consistent with the values obtained for other tangent points and Solar circle objects.

• The Bulletin of The Korean Astronomical Society
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• 제10권
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• pp.12-12
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• 1985

• Publications of The Korean Astronomical Society
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• 제19권1호
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• pp.1-10
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• 2004

On the framework of a linearly perturbed Friedmann-Robertson-Walker spacetime, we derive an expression for the cosmological angular diameter distance affected by scalar and tensor perturbations. Our expression is applicable in linear order to distances in general FRW models. We study the effect of a stocastic gravitaional wave background on the two-point correlation function of the angular diameter distance fluctuations and, on the basis of this we also derive an expression for the power spectrum of the angular diameter distance fluctuations.

• The Bulletin of The Korean Astronomical Society
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• 제46권2호
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• pp.80.3-81
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• 2021

RR Lyrae variables are excellent distance indicators thanks to their visual magnitude-metallicity relation and well-defined Period-Luminosity Relations (PLRs) at infrared wavelengths. These population II variables together with the tip of the red giant branch provide primary calibration for the first-rung of the population II distance ladder. We will present new empirical calibration of RR Lyrae PLRs at near-infrared wavelengths using our data from the ongoing CFHT-WIRCam RR Lyrae program. We will discuss the systematic uncertainties involved in the calibration of these relations based on the latest Gaia EDR3 parallaxes and the implication for the cosmic distance scale.

• The Bulletin of The Korean Astronomical Society
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• 제44권1호
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• pp.40.2-40.2
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• 2019

Measuring distances at cosmological scales is one of the most important, yet most difficult to acquire astronomical quantities, allowing astronomers to determine the expansion rate of the universe. Typically, astronomers have sought to find "standard candles" that have a known intrinsic brightness in order to determine their distance. The most well known standard candles are Type 1a supernova and Cepheid variable stars making the so-called "distance ladder". Here we present a method for determining cosmological distances via light travel-time arguments, which can be extended from nearby sources to very high redshift sources.

• Journal of The Korean Astronomical Society
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• 제29권spc1호
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• pp.89-91
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• 1996

Within the next few years eclipsing binaries should yield primary distance measurements for the Magellanic Clouds as well as provide tests of theoretical low-metallicity stellar models.

• The Bulletin of The Korean Astronomical Society
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• 제40권1호
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• pp.46.2-46.2
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• 2015

Modern methods in determining the value of the Hubble constant are divided into two main ways: the classical distance ladder method and the inverse distance ladder method. The classical distance ladder method is based on Cepheid calibrated Type Ia supernovae (SNe Ia), which are known as powerful distance indicator. The inverse distance ladder method uses cosmic microwave background radiation, which emitted from the high-z universe, and the cosmological model. Recent estimations of the Hubble constant based on these two methods show a $2{\sim}3{\sigma}$ difference, which called the "Hubble tension". It is currently an issue in the modern cosmology. We have been working on the luminosity calibration of SNe Ia based on the Tip of the Red Giant Branch (TRGB), which is a precise population I distance indicator. We present the TRGB distance estimates of 5 SNe Ia host galaxies with the archival Hubble Space Telescope image data. We derive the mean absolute maximum magnitude of 5 SNe Ia and the value of the Hubble constant. Cosmological implications of our estimate will be discussed.

• The Bulletin of The Korean Astronomical Society
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• 제12권
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• pp.5.1-5.1
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• 1987

• Journal of The Korean Astronomical Society
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• 제29권spc1호
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• pp.65-66
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• 1996