Airglow (also called nightglow) is the very weak emission of light by a planetary atmosphere. In the case of Earths atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffused sunlight from the far side are removed. The airglow phenomenon was first identified in 1868 by Swedish scientist Anders Ångström. Since then, it has been studied in the laboratory, and various chemical reactions have been observed to emit electromagnetic energy as part of the process. Scientists have identified some of those processes that would be present in Earths atmosphere, and astronomers have verified that such emissions are present. Airglow is caused by various processes in the upper atmosphere, such as the recombination of atoms, which were photoionized by the sun during the day, luminescence caused by cosmic rays striking the upper atmosphere and chemiluminescence caused mainly by oxygen and nitrogen reacting with hydroxyl ions at heights of a few hundred kilometres. It is not noticeable during the daytime because of the scattered light from the sun.
Posted on: Thu, 29 May 2014 08:16:03 +0000
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