Astronomy Picture of the Day

                         Astronomy Picture of the Day

    Discover the cosmos! [1] Each day a different image or photograph of our
 fascinating universe is featured, along with a brief explanation written by a
                           professional astronomer.

                                  2019 May 19
                                      [2]
                      A Circumhorizontal Arc Over Ohio
                  Image Credit & Copyright: Todd Sladoje [3]

Explanation: Why would clouds appear to be different colors? The reason here
is that ice crystals in distant cirrus clouds are acting like little floating
prisms [4] . Sometimes known as a fire rainbow for its flame-like appearance,
a circumhorizon arc [5]  lies parallel to the horizon. For a circumhorizontal
arc [6] to be visible, the Sun [7]  must be at least 58 degrees high in a sky
where cirrus clouds [8]  are present. Furthermore, the numerous, flat,
hexagonal ice-crystals [9] that compose the cirrus cloud [10]  must be aligned
horizontally [11] to properly refract sunlight [12]  in a collectively similar
manner. Therefore, circumhorizontal arcs [13]  are quite unusual to see. This
circumhorizon display was photographed through a polarized [14] lens [15]
above Dublin [16] , Ohio [17]  in 2009.

                      Tomorrow's picture: spinning worlds

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    Authors & editors: Robert Nemiroff [29] (MTU [30] ) & Jerry Bonnell [31]
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Site notes:
  [1] archivepix.html
  [2] image/1905/circumhorizontalarc_sladoje_2304.jpg
  [3] mailto: tsladoje at hotmail.com
  [4] http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/
  [5] http://en.wikipedia.org/wiki/Circumhorizon_arc
  [6] http://www.atoptics.co.uk/halo/cha2.htm
  [7] https://solarsystem.nasa.gov/solar-system/sun/overview/
  [8] https://en.wikipedia.org/wiki/Cirrus_cloud
  [9] http://www1.lsbu.ac.uk/water/hexagonal_ice.html
  [10] http://en.wikipedia.org/wiki/Cirrus_cloud
  [11] http://www.atoptics.co.uk/halo/platcol.htm
  [12] http://youtube.com/watch?v=U98KPM2b9IA
  [13] ap040804.html
  [14] http://en.wikipedia.org/wiki/Polarizer
  [15] http://www.youtube.com/watch?v=GTpGxIRFGoY
  [16] http://en.wikipedia.org/wiki/Dublin,_Ohio
  [17] http://en.wikipedia.org/wiki/Ohio
  [18] ap190518.html
  [19] archivepix.html
  [20] lib/apsubmit2015.html
  [21] lib/aptree.html
  [22] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [23] calendar/allyears.html
  [24] /apod.rss
  [25] lib/edlinks.html
  [26] lib/about_apod.html
  [27] http://asterisk.apod.com/discuss_apod.php?date=190519
  [28] ap190520.html
  [29] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [30] http://www.phy.mtu.edu/
  [31] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [32] http://www.astro.umd.edu/
  [33] lib/about_apod.html#srapply
  [34] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [35] https://astrophysics.gsfc.nasa.gov/
  [36] https://www.nasa.gov/
  [37] https://www.nasa.gov/centers/goddard/
  [38] http://www.mtu.edu/

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