Circumzenithal arc: Difference between revisions
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<div class="definition"><div class="short_definition">An arc centered on the [[zenith]] and found at least 46& | <div class="definition"><div class="short_definition">An arc centered on the [[zenith]] and found at least 46° above the sun (or moon).</div><br/> <div class="paragraph">It is produced by the [[refraction]] of [[light]] through the 90° prisms of [[ice crystals]], having entered through the horizontal bases and passed out through the vertical sides. Normally, the crystals are large, oriented, hexagonal plates. The circumzenithal arc is the high sky counterpart of the [[circumhorizontal arc|circumhorizontal arc]]. The circumhorizontal arc is low in the sky when the sun is high (above 58° [[elevation]]); the circumzenithal arc is high in the sky when the sun is low (below 32° elevation). The majority of circumzenithal arcs are short-lived, short in length and faint or moderately bright. However, very colorful circumhorizontal arcs can occur when the refraction is close to the minimum angle of deviation, corresponding to a solar [[elevation angle]] of about 22°.</div><br/> </div> | ||
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Latest revision as of 15:36, 25 April 2012
circumzenithal arc
An arc centered on the zenith and found at least 46° above the sun (or moon).
It is produced by the refraction of light through the 90° prisms of ice crystals, having entered through the horizontal bases and passed out through the vertical sides. Normally, the crystals are large, oriented, hexagonal plates. The circumzenithal arc is the high sky counterpart of the circumhorizontal arc. The circumhorizontal arc is low in the sky when the sun is high (above 58° elevation); the circumzenithal arc is high in the sky when the sun is low (below 32° elevation). The majority of circumzenithal arcs are short-lived, short in length and faint or moderately bright. However, very colorful circumhorizontal arcs can occur when the refraction is close to the minimum angle of deviation, corresponding to a solar elevation angle of about 22°.
