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Twinkling, or scintillation, is a generic term for variations in apparent brightness or position of a distant luminous object viewed through a medium.〔Wang,Ting-I; Williams, Donn; ("Scintillation technology bests NIST" ), ''InTech'', May 1, 2005〕 If the object lies outside the Earth's atmosphere, as in the case of stars and planets, the phenomenon is termed ''astronomical scintillation;'' within the atmosphere, the phenomenon is termed ''terrestrial scintillation.''〔(" NASA Aerospace Science and Technology Dictionary" ), ''NASA.gov''〕 As one of the three principal factors governing astronomical seeing, atmospheric twinkling is defined as variations in illuminance only. In simple terms, twinkling of stars is caused by the passing of light through different layers of a turbulent atmosphere. Most scintillation effects are caused by anomalous refraction caused by small-scale fluctuations in air density usually related to temperature gradients.〔Sofieva, V. F.; Sofieva, A.S.; et al ("Reconstruction of internal gravity wave and turbulence parameters in the stratosphere using GOMOS scintillation measurements" ) ''Journal of Geophysical Research'' 112〕〔VanCleave, Janice; ("Stellar Scintillation: Twinkling Stars" ) ''JVC's Science Fair Projects'', May 2, 2010〕 Scintillation effects are always much more pronounced near the horizon than near the zenith (straight up),〔("Scintillation or Atmospheric Boil" ), ''noaa.gov''〕 since the light near the horizon passes through a thicker layer of atmosphere. Atmospheric twinkling is measured quantitatively using a scintillometer.〔Chun, M.; Avila, R; ("Turbulence profiling using a scanning scintillometer" ), ''Astronomical Site Evaluation in the Visible and Radio Range'', Astronomical Society of the Pacific 266:72-78〕 The effects of twinkling are reduced by using a larger receiver aperture. This effect is known as ''aperture averaging''.〔Perlot,.N.; Fritzsche, D. ("Aperture-Averaging - Theory and Measurements" ), ''elib - Electronic Library''〕 While light from planets, stars and other astronomical objects are likely to twinkle,〔Wheelon, Albert D. ("Electromagnetic Scintillation: Volume 2, Weak Scattering" ), ''Cambridge University Press,'' Jul 31, 2003〕 twinkling does not cause images of planets to flicker appreciably.〔Kenyon, S.L.; Lawrence, M. et al; ("Atmospheric Scintillation at Dome C, Antarctica" ), ''Astronomical Society of the Pacific'' 118 924-932〕 Stars twinkle because they are so far from Earth that they appear as point sources of light easily disturbed by Earth's atmospheric turbulence which acts like lenses and prisms diverting the light's path. Large astronomical objects closer to Earth, like the Moon and other planets, encompass many points in space and can be resolved as objects with observable diameters. With multiple observed points of light traversing the atmosphere, their light's deviations average out and the viewer perceives less variation in light coming from them.〔Graham, John A. ("Why do stars twinkle?" ) ''Scientific American,'' October 2005〕〔Byrd, Deborah; ("Why don’t planets twinkle as stars do?" ), ''Earthsky,'' October 24, 2005〕 ==See also== * Astronomical seeing * Earth's atmosphere * Interplanetary scintillation * Observational astronomy * Twinkle Twinkle Little Star * Scintillation (disambiguation) * Twinkle (disambiguation) 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「Twinkling」の詳細全文を読む スポンサード リンク
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