                  APOD: 2017 July 21 - Phobos: Moon over Mars

                         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 July 21
                                      [2]
                            Phobos: Moon over Mars
  Image Credit: NASA [3] , ESA [4] , Zolt Levay (STScI [5] ) - Acknowledgment:
                   J.Bell (ASU [6] ) and M.Wolff (SSI [7] )

Explanation: A tiny moon with a scary name [8] , Phobos emerges from behind
the Red Planet in this timelapse sequence from the Earth-orbiting Hubble Space
Telescope [9] . Over 22 minutes the 13 separate exposures were captured near
the 2016 closest approach of Mars [10]  to planet Earth. Martians [11]  have
to look to the west to watch Phobos rise, though. The small moon is closer to
its parent planet [12]  than any other moon in the Solar System, about 3,700
miles (6,000 kilometers) above the Martian surface [13] . It completes one
orbit in just 7 hours and 39 minutes. That's faster than a Mars rotation,
which corresponds to about 24 hours and 40 minutes. So on Mars, Phobos can be
seen to rise above the western horizon 3 times a day. Still, Phobos is doomed
[14] .

                  Tomorrow's picture: to catch some sun [15]

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    Authors & editors: Robert Nemiroff [27] (MTU [28] ) & Jerry Bonnell [29]
                                  (UMCP [30] )
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                           & Michigan Tech. U. [36]
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Site notes:
  [1] archivepix.html
  [2] image/1707/STSCI-MarsPhobosComp3000.jpg
  [3] http://www.nasa.gov/
  [4] http://www.spacetelescope.org/
  [5] http://www.stsci.edu/
  [6] https://sese.asu.edu/
  [7] http://www.spacescience.org/
  [8] https://www.nasa.gov/feature/goddard/2017/
hubble-sees-martian-moon-orbiting-the-red-planet
  [9] http://hubblesite.org/image/4061/news_release/2017-29
  [10] ap160809.html
  [11] ap150516.html
  [12] ap031024.html
  [13] ap031129.html
  [14] ap121028.html
  [15] ap170722.html
  [16] ap170720.html
  [17] archivepix.html
  [18] lib/apsubmit2015.html
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  [26] ap170722.html
  [27] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [28] http://www.phy.mtu.edu/
  [29] http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
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