              APOD: 2017 September 17 - Bright Spiral Galaxy M81

                         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 17
                                      [2]
                          Bright Spiral Galaxy M81
 Image Credit: Subaru Telescope [3] (NAOJ [4] ), Hubble Space Telescope [5] ;
      Processing & Copyright: Roberto Colombari [6]  & Robert Gendler [7]

Explanation: One of the brightest galaxies in planet Earth's sky is similar in
size to our Milky Way [8]  Galaxy: big, beautiful M81 [9] . This grand spiral
galaxy [10]  can be found toward the northern constellation of the Great Bear
[11] (Ursa Major [12] ). This superbly detailed view [13]  reveals M81's
bright yellow nucleus, blue spiral arms, and sweeping cosmic dust lanes with a
scale comparable to the Milky Way [14] . Hinting at a disorderly past [15] , a
remarkable dust lane actually runs straight through the disk, to the left of
the galactic center, contrary to M81 [16] 's other prominent spiral [17]
features. The errant dust lane [18]  may be the lingering result of a close
encounter [19]  between M81 [20] and its smaller companion galaxy, M82 [21] .
Scrutiny of variable stars [22]  in M81 [23]  has yielded one of the best
determined distances [24]  for an external galaxy -- 11.8 million light-years.

                  Free Download: The 2018 APOD Calendar [25]
                    Tomorrow's picture: easter orion [26]

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Site notes:
  [1] archivepix.html
  [2] image/1709/m81_colombari_3200c.jpg
  [3] http://www.naoj.org/Introduction/index.html
  [4] http://www.naoj.org/
  [5] http://hla.stsci.edu/hla_welcome.html
  [6] http://www.astrobin.com/users/rob77/
  [7] http://www.robgendlerastropics.com/
  [8] http://www.atlasoftheuniverse.com/galaxy.html
  [9] ap060707.html
  [10] https://www.nasa.gov/multimedia/imagegallery/image_feature_2132.html
  [11] http://en.wikipedia.org/wiki/Bear
  [12] http://en.wikipedia.org/wiki/Ursa_Major
  [13] http://www.astrobin.com/123777/0/?mod=solved
  [14] http://casswww.ucsd.edu/archive/public/tutorial/MW.html
  [15]
http://stories.barkpost.com/wp-content/uploads/2015/04/
chihuahua-toilet-paper.jpg
  [16] ap130416.html
  [17] http://burro.astr.cwru.edu/Academics/Astr222/Galaxies/Spiral/
spiral.html
  [18] ap010112.html
  [19] ap130925.html
  [20] https://en.wikipedia.org/wiki/Messier_81
  [21] ap120326.html
  [22] https://www.aavso.org/
  [23] https://www.youtube.com/watch?v=7-H5NBCGVtg
  [24] http://www.ipac.caltech.edu/H0kp/m81/m81.html
  [25] https://apod.nasa.gov/apod/fap/APOD_Calendar_2018_300dpi.pdf
  [26] ap170918.html
  [27] ap170916.html
  [28] archivepix.html
  [29] lib/apsubmit2015.html
  [30] lib/aptree.html
  [31] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [32] calendar/allyears.html
  [33] /apod.rss
  [34] lib/edlinks.html
  [35] lib/about_apod.html
  [36] http://asterisk.apod.com/discuss_apod.php?date=170917
  [37] ap170918.html
  [38] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [39] http://www.phy.mtu.edu/
  [40] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [41] http://www.astro.umd.edu/
  [42] lib/about_apod.html#srapply
  [43] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [44] https://astrophysics.gsfc.nasa.gov/
  [45] https://www.nasa.gov/
  [46] https://www.nasa.gov/centers/goddard/
  [47] http://www.mtu.edu/
