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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Gravity darkening ： ウィキペディア英語版 Gravity darkening Gravity darkening, also referred to as gravity brightening, is an astronomical phenomenon where a star rotates so rapidly that it has a detectably oblate spheroid shape, such as in Regulus in the constellation Leo. When a star is oblate, it has a larger radius at its equator than it does at its poles. As a result, the poles have a higher surface gravity, and thus higher temperature and brightness. Thus, the poles are "gravity brightened", and the equator "gravity darkened". The star becomes oblate (and hence gravity darkening occurs) because the centrifugal force resulting from rotation creates additional outward pressure on the star. The centrifugal force is expressed mathematically as :$F\_\{\backslash text\{centrifugal\}\}\; =\; m\; \backslash Omega^2\; \backslash rho$ where $m$ is mass (in this case of a small volume element of the star), $\backslash Omega$ is the angular velocity, and $\backslash rho$ is the radial distance from the axis of rotation. In the case of a star, the value of $\backslash rho$ is largest at the equator and smallest at the poles. This means that equatorial regions of a star will have a greater centrifugal force when compared to the pole. The centrifugal force pushes mass away from the axis of rotation, and results in less overall pressure on the gas in the equatorial regions of the star. This will cause the gas in this region to become less dense, and cooler. ==See also== *Von Zeipel theorem 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravity darkening」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.