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Related to geocorona: Lagrangian point
geocorona(jee-oh-kŏ-roh -nă) A tenuous cloud of hydrogen and some helium extending more than 50 000 km from the Earth's outermost atmospheric layer to the magnetosphere. It scatters Lyman-alpha radiation (see Lyman series) from the Sun, producing a glow that is visible on long-distance far-ultraviolet photographs of the Earth. It also interferes with far-ultraviolet astronomical observations from Earth orbit.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The outermost part of the earth's atmosphere, consisting of extremely attenuated hydrogen extending to perhaps 15 earth radii, that emits Lyman-alpha radiation under the action of sunlight.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.