                  APOD: 2018 January 1 - Sun Halo over Sweden

                         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 January 1
                            Sun Halo over Sweden
 Video Credit & Copyright: Hkan Hammar [2] (Vemdalen Ski Resort [3] , SkiStar
                                    [4] )

Explanation: What's happened to the Sun? Sometimes it looks like the Sun is
being viewed through a giant lens [5] . In the featured video, however, there
are actually millions of tiny lenses: ice crystals [6] . Water may freeze in
the atmosphere [7]  into small, flat, six-sided, ice crystals. As these
crystals [8]  flutter to the ground, much time is spent with their faces flat
and parallel [9]  to the ground. An observer [10]  may find themselves in the
same plane as many of the falling ice crystals near sunrise or sunset. During
this alignment, each crystal can act like a miniature lens, refracting
sunlight into our view [11]  and creating phenomena like parhelia [12] , the
technical term for sundogs [13] . The featured video [14]  was taken a month
ago on the side of a ski hill at the Vemdalen Ski Resort [15]  near Stockholm
[16] , Sweden [17] . Visible in the center is the most direct image of the Sun
[18] , while two bright sundogs [19]  glow prominently from both the left and
the right. Also visible [20]  is the bright 22 degree halo [21]  -- as well as
the rarer and much fainter 46 degree halo [22]  -- also created by sunlight
reflecting [23]  off of atmospheric ice crystals [24] .

                  Tomorrow's picture: unexpected x-rays [25]

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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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              A service of: ASD [43]  at NASA [44]  / GSFC [45]
                           & Michigan Tech. U. [46]
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Site notes:
  [1] archivepix.html
  [2] https://www.facebook.com/hakanhf
  [3] https://www.skistar.com/sv/vemdalen/
  [4] https://www.skistar.com/en/About-SkiStar/
  [5] https://en.wikipedia.org/wiki/Lens_(optics)
  [6] http://www.its.caltech.edu/~atomic/snowcrystals/halos/halos.htm
  [7]
https://www.nasa.gov/sites/default/files/images/
463940main_atmosphere-layers2_full.jpg
  [8] http://en.wikipedia.org/wiki/Ice_crystal
  [9] https://www.atoptics.co.uk/halo/orplate.htm
  [10] http://littlefun.org/uploads/52410bb8e691b267f97d9278_736.jpg
  [11] ap100208.html
  [12] http://www.atoptics.co.uk/halo/parhelia.htm
  [13] ap990823.html
  [14] https://www.facebook.com/hakanhf/videos/10210053095156104/
  [15] https://www.skistar.com/en/Vemdalen/About-Vemdalen/
  [16] http://en.wikipedia.org/wiki/Stockholm
  [17] http://en.wikipedia.org/wiki/Sweden
  [18] https://solarsystem.nasa.gov/planets/sun
  [19] http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/sd.rxml
  [20] http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/halo.html
  [21] http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/halo22.html
  [22] http://www.atoptics.co.uk/halo/46hal.htm
  [23] http://www.atoptics.co.uk/halo/circular.htm
  [24] ap080618.html
  [25] ap180102.html
  [26] ap171231.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=180101
  [36] ap180102.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/
