              APOD: 2017 September 23 - A Conjunction of Comets

                         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.

                              2017 September 23
                                      [2]
                           A Conjunction of Comets
    Image Credit & Copyright [3] : Jose J. Chambo [4] (Cometografia [5] )

Explanation: A conjunction of comets [6] is captured in this pretty star field
[7] from the morning of September 17. Discovered in July by a robotic sky
survey searching for supernovae [8] , comet C/2017 O1 ASASSN [9] is at the
lower left. The visible greenish glow of its coma is produced by the
fluorescence of diatomic carbon molecules in sunlight. Nearing its closest
approach to the Sun, the binocular comet was only about 7.2 light-minutes from
Earth. In the same telescopic field of view is the long-tailed, outbound comet
C/2015 ER61 PanSTARRS [10]  at the upper right, almost 14 light-minutes away.
Many light-years distant, the starry background includes faint, dusty nebulae
of the Milky Way. The well-known Pleiades star cluster lies just off the top
right of the frame.

                   Tomorrow's picture: a light unknown [11]

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    Authors & editors: Robert Nemiroff [23] (MTU [24] ) & Jerry Bonnell [25]
                                  (UMCP [26] )
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Site notes:
  [1] archivepix.html
  [2] image/1709/2017O1&2015ER61_170917_2400_clean.jpg
  [3] lib/about_apod.html#srapply
  [4] http://cometografia.es/acerca-de/contactar/
  [5] http://cometografia.es/
  [6] https://solarsystem.nasa.gov/planets/comets
  [7] http://cometografia.es/ 2017o1-asassn-2015er61-panstarrs-20170917/
  [8] http://www.astronomy.ohio-state.edu/~assassin/index.shtml
  [9] http://cometchasing.skyhound.com/
  [10] http://aerith.net/comet/catalog/2015ER61/2015ER61.html
  [11] ap170924.html
  [12] ap170922.html
  [13] archivepix.html
  [14] lib/apsubmit2015.html
  [15] lib/aptree.html
  [16] http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [17] calendar/allyears.html
  [18] /apod.rss
  [19] lib/edlinks.html
  [20] lib/about_apod.html
  [21] http://asterisk.apod.com/discuss_apod.php?date=170923
  [22] ap170924.html
  [23] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [24] http://www.phy.mtu.edu/
  [25] http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [26] http://www.astro.umd.edu/
  [27] lib/about_apod.html#srapply
  [28] http://www.nasa.gov/about/highlights/HP_Privacy.html
  [29] http://astrophysics.gsfc.nasa.gov/
  [30] http://www.nasa.gov/
  [31] http://www.nasa.gov/centers/goddard/
  [32] http://www.mtu.edu/
