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Cloud iridescence
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<h2 id="etymology">Etymology</h2> <p>Irisations are named after the Greek goddess <a href="/facts/Iris_(mythology)/IhXsu877">Iris</a>, goddess of <a href="/facts/Rainbow/rBvLyu3u">rainbows</a> and messenger of <a href="/facts/Zeus/9wTwkEDt">Zeus</a> and <a href="/facts/Hera/Jw5Km2DP">Hera</a> to the mortals below.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="mechanism">Mechanism</h2> <p>Iridescent clouds are a <a href="/facts/Diffraction/Mk80xXHT">diffraction</a> phenomenon caused by small <a href="/facts/Drop_(liquid)/m4kuGAgH">water droplets</a> or small <a href="/facts/Ice_crystals/By1nPMgF">ice crystals</a> individually <a href="/facts/Light_scattering_by_particles/pyNaTyrj">scattering light</a>. Larger ice crystals do not produce iridescence, but can cause <a href="/facts/Halo_(optical_phenomenon)/QgmnIgWQ">halos</a>, a different phenomenon.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p><p>Irisation is caused by very uniform water droplets <a href="/facts/Diffraction/Mk80xXHT">diffracting</a> light (within 10 degrees from the <a href="/facts/Sun/CadPCVHh">Sun</a>) and by first order <a href="/facts/Interference_(wave_propagation)/lI5f78I4">interference</a> effects<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> (beyond about 10 degrees from the Sun). It can extend up to 40 degrees from the Sun.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>If parts of clouds contain small water droplets or ice crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-<a href="/facts/Transparency_and_translucency/PRryNNW6">transparent</a> clouds, while newly forming clouds produce the brightest and most colorful iridescence. When the particles in a thin cloud are very similar in size over a large extent, the iridescence takes on the structured form of a <a href="/facts/Corona_(optical_phenomenon)/waVYWgh6">corona</a>, a bright circular disk around the Sun or Moon surrounded by one or more colored rings.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a><a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="gallery">Gallery</h2> <h2 id="see-also">See also</h2> <ul> <li>Weather portal</li></ul> <ul><li><a href="/facts/Polar_stratospheric_cloud/wpQfDlBI">Polar stratospheric cloud</a></li> <li><a href="/facts/Circumhorizontal_arc/5jo6egef">Circumhorizontal arc</a></li> <li><a href="/facts/Noctilucent_cloud/9qYNj7EG">Noctilucent cloud</a></li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Iridescent clouds. Look up <i>iridescent cloud</i> in Wiktionary, the free dictionary. <ul><li><a href="http://www.atoptics.co.uk/droplets/iridim0.htm">Iridescent cloud gallery – Atmospheric Optics site</a></li> <li><a href="http://chestofbooks.com/crafts/scientific-american/sup5/On-The-Cause-Of-Iridescence-In-Clouds.html">On the Cause of Iridescence in Clouds</a> – <a href="/facts/Scientific_American/jkl8bhUN">Scientific American</a> Supplement</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Gedzelman, Stanley David (1 June 1988). "In Praise of Altocumulus". Weatherwise. 41 (3): 143–149. doi:10.1080/00431672.1988.9930533. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Answers.com – Sci-Tech Dictionary: irisation <a href="http://www.answers.com/topic/irisation-meteorology" target="_blank">http://www.answers.com/topic/irisation-meteorology</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Nemiroff, R.; Bonnell, J., eds. (25 November 2007). "An Iridescent Cloud Over Colorado". Astronomy Picture of the Day. NASA. <a href="https://apod.nasa.gov/apod/ap071125.html" target="_blank">https://apod.nasa.gov/apod/ap071125.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Iridescent Clouds". Atmospheric Optics. <a href="http://www.atoptics.co.uk/droplets/irid1.htm" target="_blank">http://www.atoptics.co.uk/droplets/irid1.htm</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Sassen, Kenneth (1 January 2003). "Cirrus cloud iridescence: a rare case study". Applied Optics. 42 (3): 486–491. Bibcode:2003ApOpt..42..486S. doi:10.1364/AO.42.000486. PMID 12570270. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Nacreous Clouds". Atmospheric Optics. <a href="https://www.atoptics.co.uk/highsky/nacr1.htm" target="_blank">https://www.atoptics.co.uk/highsky/nacr1.htm</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>PHOTOMETEORS, by Jesús Martínez-Frías Archived 2009-12-13 at the Wayback Machine <a href="http://tierra.rediris.es/megacryometeors/photometeors.pdf" target="_blank">http://tierra.rediris.es/megacryometeors/photometeors.pdf</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>The Cloudspotter's Guide By Gavin Pretor-Pinney, p. 233 <a href="https://books.google.com/books?id=MAiKY4xU6y8C&pg=PA233&dq=Cloud+iridescence+Irisation&lr=" target="_blank">https://books.google.com/books?id=MAiKY4xU6y8C&pg=PA233&dq=Cloud+iridescence+Irisation&lr=</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Cloud Iridescence | SKYbrary Aviation Safety". skybrary.aero. Retrieved 2022-08-19. <a href="https://skybrary.aero/articles/cloud-iridescence" target="_blank">https://skybrary.aero/articles/cloud-iridescence</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Color and Light in Nature By David K. Lynch, William Charles Livingston, p. 133 <a href="https://books.google.com/books?id=4Abp5FdhskAC&pg=PA133&dq=Cloud+iridescence+Irisation&lr=" target="_blank">https://books.google.com/books?id=4Abp5FdhskAC&pg=PA133&dq=Cloud+iridescence+Irisation&lr=</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>PHOTOMETEORS, by Jesús Martínez-Frías Archived 2009-12-13 at the Wayback Machine <a href="http://tierra.rediris.es/megacryometeors/photometeors.pdf" target="_blank">http://tierra.rediris.es/megacryometeors/photometeors.pdf</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"Cloud Iridescence | SKYbrary Aviation Safety". skybrary.aero. Retrieved 2022-08-19. <a href="https://skybrary.aero/articles/cloud-iridescence" target="_blank">https://skybrary.aero/articles/cloud-iridescence</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"Corona". Atmospheric Optics. <a href="http://www.atoptics.co.uk/droplets/corona.htm" target="_blank">http://www.atoptics.co.uk/droplets/corona.htm</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Shaw, Joseph A.; Pust, Nathan (12 August 2011). "Icy wave-cloud lunar corona and cirrus iridescence". Applied Optics. 50 (28): F6. Bibcode:2011ApOpt..50F...6S. doi:10.1364/AO.50.0000F6. PMID 22016246. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> </ol>