Subj : Daily APOD Report To : All From : Ben Ritchey Date : Sun May 19 2019 13:48:28 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 ------------------------------------------------------------------------------- < [18] | Archive [19] | Submissions [20] | Index [21] | Search [22] | Calendar [23] | RSS [24] | Education [25] | About APOD [26] | Discuss [27] | > [28] ------------------------------------------------------------------------------- Authors & editors: Robert Nemiroff [29] (MTU [30] ) & Jerry Bonnell [31] (UMCP [32] ) NASA Official: Phillip Newman Specific rights apply [33] . NASA Web Privacy Policy and Important Notices [34] A service of: ASD [35] at NASA [36] / GSFC [37] & Michigan Tech. U. [38] ---------- 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/ --- Mystic BBS v1.12 A43 (Windows/32) * Origin: FIDONet - The Positronium Repository (1:393/68) .