                APOD: 2018 May 2 - Moon Halo over Stone Circle

                         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.

                                  2018 May 2
                                      [2]
                         Moon Halo over Stone Circle
            Image Credit & Copyright: Alyn Wallace Photography [3]

Explanation: Have you ever seen a halo around the Moon [4] ? This fairly
common sight occurs when high thin clouds [5]  containing millions of tiny ice
crystals [6]  cover much of the sky. Each ice crystal [7]  acts like a
miniature lens. Because most [8] of the crystals have a similar elongated
hexagonal shape, light entering one crystal face and exiting through the
opposing face refracts 22 degrees, which corresponds to the radius of the Moon
Halo [9] . A similar Sun Halo [10] may be visible during the day. Exactly how
ice-crystals form [11] in clouds remains under investigation. In the featured
image [12] , the ice circle in the sky [13]  is mirrored by a stone circle
[14]  on the ground. Taken just over a month ago in Pontypridd Common [15] ,
Wales [16] , UK [17] , the central Rocking Stone [18]  survives from the last
[19] ice age [20] , while the surrounding stones in the circles were placed
much more recently -- during the 1800s.

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    Authors & editors: Robert Nemiroff [37] (MTU [38] ) & Jerry Bonnell [39]
                                  (UMCP [40] )
          NASA Official:  Phillip Newman Specific rights apply [41] .
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Site notes:
  [1] archivepix.html
  [2] image/1805/StoneHalo_Wallace_2048.jpg
  [3] https://alynwallacephotography.com/
  [4] https://solarsystem.nasa.gov/moons/earths-moon/in-depth/
  [5] https://en.wikipedia.org/wiki/Cirrus_cloud
  [6] http://en.wikipedia.org/wiki/Ice_crystals
  [7] https://www.atoptics.co.uk/halo/circ1.htm
  [8] http://www.everythingweather.com/lightning/ice.shtml
  [9] https://www.atoptics.co.uk/halo/circmoon.htm
  [10] ap150403.html
  [11]
http://www.cas.manchester.ac.uk/resactivities/cloudphysics/topics/formation/
  [12]
https://www.facebook.com/alynwallace/photos/
a.431610087022885.1073741827.414849302032297/779521125565111/?type=3&theater
  [13] https://www.atoptics.co.uk/halo/circular.htm
  [14]
https://www.rctcbc.gov.uk/EN/Tourism/Thingstodo/HistoryandHeritage/
MythsLegendsHeroesStories/TheRockingStones.aspx
  [15] https://www.youtube.com/watch?v=YPwDB8KvjyE
  [16] https://www.youtube.com/watch?v=IcdDIWqpVlA
  [17] https://en.wikipedia.org/wiki/United_Kingdom
  [18] https://en.wikipedia.org/wiki/Rocking_stone
  [19] https://en.wikipedia.org/wiki/Last_Glacial_Maximum
  [20] https://en.wikipedia.org/wiki/Ice_age
  [21] https://www.facebook.com/AstronomyPictureOfTheDay
  [22] https://plus.google.com/u/1/+AstronomyPictureOfTheDay
  [23] https://www.instagram.com/astronomypicturesdaily/
  [24] http://twitter.com/apod/
  [25] ap180503.html
  [26] ap180501.html
  [27] archivepix.html
  [28] lib/apsubmit2015.html
  [29] lib/aptree.html
  [30] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [31] calendar/allyears.html
  [32] /apod.rss
  [33] lib/edlinks.html
  [34] lib/about_apod.html
  [35] http://asterisk.apod.com/discuss_apod.php?date=180502
  [36] ap180503.html
  [37] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [38] http://www.phy.mtu.edu/
  [39] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [40] http://www.astro.umd.edu/
  [41] lib/about_apod.html#srapply
  [42] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [43] https://astrophysics.gsfc.nasa.gov/
  [44] https://www.nasa.gov/
  [45] https://www.nasa.gov/centers/goddard/
  [46] http://www.mtu.edu/
