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The
shadow of the Earth cast upon an evening twilit sky. Photographed
in Chile, November 2000, by Marko Riikonen (site).
The view is from the lower flanks of Aucanquilcha volcano looking
east to Bolivia. ©Marko Riikonen |
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After sunset
look eastwards. A low horizon is
needed but not a volcano. As twilight deepens a dark band rises
upwards from the horizon, The band is the shadow of the Earth on
the atmosphere. Immediately above, where the evening air is still
lit, glows a pink band called the anti-twilight arch or "Belt
of Venus". The pink arises from scattered and deeply reddened
sunlight mingling with the deep blues of the eastern sky. Look westwards
before sunrise to watch the shadow sinking towards the horizon.
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The
Earth's Shadow. As the sun sinks deeper below the
horizon, the Earth's shadow rises in the east. The shadow is a three
dimensional void of unlit atmosphere. The sky high above the shadowed
air is bright because it is still sunlit and the air scatters light
down to the eye. This diagram is not to scale! The atmosphere is a
thin skin compared to the diameter of the earth. |
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