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Ashen light is a hypothesised subtle glow that has been claimed to be seen coming from the night side of the planet Venus. Yet some claim it is of doubtful existence. Its causes remain controversial, but it seems that Ashen light is principally a dusk side phenomenon associated with lightning on Venus.〔 == History of observations== Ashen light was first sighted by the astronomer Giovanni Battista Riccioli on January 9, 1643, and he named it "The Ashen Light of Venus." Subsequent claims have been made by various observers including Sir William Herschel, Sir Patrick Moore, Dale P. Cruikshank, Nikolai Kozyrev and William K. Hartmann.〔 〕 Ashen Light has been most often sighted when Venus was in the evening sky, when the evening terminator of the planet is toward the Earth.〔 However nobody has managed to capture an image of Ashen light.〔 The Ashen light ought to be visible when a crescent Venus is occulted by a crescent Moon, such that the unilluminated portion of Venus can be seen against the dark side of the Moon, and with the illuminated portion of Venus being obscured. The first documented attempt was made on 2001 Jul 17 from the Marshall Islands, with a 67% Venus reappearing from behind a 13% Moon. None of the several visual observers (including those using two 61cm 'Super RADOTS' telescopes) reported seeing the ashen light. The event was also videoed, but the camera was too insensitive to detect even the earthshine.〔(2001 Jul 17 Reappearance of Venus from the Marshall Islands ), by Peter Rejcek. See page 8. Retrieved 2015-10-25.〕 A particularly favourable instance occurred on 2015 October 8, with a 40% illuminated Venus reappearing from behind the unlit limb of a 15% sunlit Moon. The event was visible in dark skies throughout Central Australia and was recorded by David and Joan Dunham (of the International Occultation Timing Association) using a 10" f/4 Newtonian with a Watec 120N+ video camera from a location just north of Alice Springs. They also observed the event visually with an 8" SCT telescope. Neither the real-time visual observation nor close visual inspection of the video recording showed any sign of the dark side of Venus.〔(2015 October 8 Reappearance of Venus from Australia ), by Dunham D.W. & J.B. (2015-Oct-08).〕 While not conclusive, these observations suggest the ashen light is more likely attributable to telescope optics and eye physiology rather than atmospheric phenomena on Venus. The Keck telescope on Hawaii reported seeing a subtle green glow and suggested it could be produced as ultraviolet light from the Sun splits molecules of carbon dioxide (), known to be common in Venus' atmosphere, into carbon monoxide () and oxygen (), but the green light emitted as oxygen recombines to form is thought too faint to explain the effect,〔 and it is too faint to have been observed with amateur telescopes. 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「Ashen light」の詳細全文を読む スポンサード リンク
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