Dark segment: Difference between revisions

Latest revision as of 11:55, 27 March 2024

A blue or bluish gray wedge seen in the antisolar sky between the astronomical horizon and the pink, orange, or purple antitwilight arch.
During clear twilights, the dark segment is visible (assuming a flat horizon) at sun elevations ∼ -0.5° > h₀ > -7°. The dark segment is sometimes called the earth's shadow since one of its causes is the sunlight shadow that the earth casts on the nearby atmosphere. However, atmospheric scattering and extinction make the dark segment's luminance and color distribution more complicated than that for simple shadows. For example, the dark segment's vertical width above the antisolar point is consistently greater than , contrary to the behavior of a simple geometric shadow.

Reference: R. L. Lee, Jr., "Measuring and modeling twilight’s Belt of Venus," Applied Optics, v. 54 (2015), pp. B194-B203.

term edited 5 Oct 2015

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+A blue or bluish gray wedge seen in the antisolar sky between the [[astronomical horizon|astronomical  horizon]] and the pink, orange, or purple [[antitwilight arch]].<br/> During [[clear]] twilights, the dark segment is visible (assuming a flat [[horizon]]) at sun elevations  &sim; -0.5&#x000b0; &gt; ''h''<sub>0</sub> &gt; -7&#x000b0;. The dark segment is sometimes called the [[earth's shadow]] since one of its  causes is the [[sunlight]] shadow that the earth casts on the nearby [[atmosphere]]. However, atmospheric  [[scattering]] and [[extinction]] make the dark segment's [[luminance]] and color distribution more complicated  than that for simple shadows. For example, the dark segment's vertical width above the  [[antisolar point]] is consistently greater than [[File:ams2001glos-Dex01.gif|link=|ams2001glos-Dex01]], contrary to the behavior of a simple geometric  shadow.<br/>
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+Reference:
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+R. L. Lee, Jr., "Measuring and modeling twilight’s Belt of Venus," ''Applied Optics'', v. '''54''' (2015), pp. B194-B203.
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+''term edited 5 Oct 2015''
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-== dark segment ==
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-<div class="definition"><div class="short_definition">A blue or bluish gray wedge seen in the antisolar sky between the [[astronomical horizon|astronomical  horizon]] and the pink, orange, or purple [[antitwilight arch]].</div><br/> <div class="paragraph">During [[clear]] twilights, the dark segment is visible (assuming a flat [[horizon]]) at sun elevations  &sim; -0.5&#x000b0; &lt; ''h''<sub>0</sub> &lt; -7&#x000b0;. The dark segment is sometimes called the [[earth's shadow]] since one of its  causes is the [[sunlight]] shadow that the earth casts on the nearby [[atmosphere]]. However, atmospheric  [[scattering]] and [[extinction]] make the dark segment's [[luminance]] and color distribution more complicated  than that for simple shadows. For example, the dark segment's vertical width above the  [[antisolar point]] is consistently greater than <div class="inline-formula">[[File:ams2001glos-Dex01.gif|link=|ams2001glos-Dex01]]</div>, contrary to the behavior of a simple geometric  shadow.</div><br/> </div>
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