            APOD: 2018 January 15 - Rigel and the Witch Head Nebula

                         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 15
                                      [2]
                       Rigel and the Witch Head Nebula
          Image Credit & Copyright: Mario Cogo [3] (Galax Lux [4] )

Explanation: By starlight this eerie visage shines in the dark, a crooked
profile evoking its popular name, the Witch Head Nebula [5] . In fact, this
entrancing telescopic portrait [6]  gives the impression that the witch has
fixed her gaze on Orion's bright supergiant star Rigel [7] . More formally
known as IC 2118 [8] , the Witch Head Nebula spans about 50 light-years and is
composed of interstellar dust grains reflecting Rigel's [9] starlight. The
blue color of the Witch Head Nebula and of the dust surrounding Rigel [10] is
caused not only by Rigel [11] 's intense blue starlight but because the dust
grains scatter blue light [12]  more efficiently than red. The same physical
process [13]  causes Earth's daytime sky to appear blue [14] , although the
scatterers in Earth's atmosphere [15]  are molecules of nitrogen and oxygen.
Rigel, the Witch Head Nebula, and gas and dust that surrounds them lie about
800 light-years [16]  away.

Open Science: Browse 1,600+ codes in the Astrophysics Source Code Library [17]

                  Tomorrow's picture: high and far-off [18]

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Site notes:
  [1] archivepix.html
  [2] image/1801/Witchhead_Cogo_1024.jpg
  [3] http://galaxlux.com/Author.htm
  [4] http://galaxlux.com/index.html
  [5] ap061211.html
  [6] http://galaxlux.com/Rigel%20Witch%20Head%20Nebula.htm
  [7] https://en.wikipedia.org/wiki/Rigel
  [8] http://en.wikipedia.org/wiki/IC_2118
  [9] http://adsabs.harvard.edu/abs/1997MNRAS.290..521I
  [10] http://www.youtube.com/watch?v=c8CgDGhYKe8
  [11] http://stars.astro.illinois.edu/sow/rigel.html
  [12] http://leo.astronomy.cz/mix/mix.html
  [13] http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
  [14] http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
  [15] https://spaceplace.nasa.gov/atmosphere/en/
  [16] http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html
  [17] http://ascl.net/code/all
  [18] ap180116.html
  [19] ap180114.html
  [20] archivepix.html
  [21] lib/apsubmit2015.html
  [22] lib/aptree.html
  [23] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [24] calendar/allyears.html
  [25] /apod.rss
  [26] lib/edlinks.html
  [27] lib/about_apod.html
  [28] http://asterisk.apod.com/discuss_apod.php?date=180115
  [29] ap180116.html
  [30] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [31] http://www.phy.mtu.edu/
  [32] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [33] http://www.astro.umd.edu/
  [34] lib/about_apod.html#srapply
  [35] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [36] https://astrophysics.gsfc.nasa.gov/
  [37] https://www.nasa.gov/
  [38] https://www.nasa.gov/centers/goddard/
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