Astronomy Picture of the Day

                         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 September 12
                                  Lunations
  Video Credit: Data:  Lunar Reconnaissance Orbiter [2]  ; Animation: NASA [3]
                   's Scientific Visualization Studio [4] ;
             Music:  The Blue Danube [5] (Johann Strauss II [6] )

Explanation: Our Moon's appearance changes nightly. As the Moon [7]  orbits
the Earth [8] , the half illuminated by the Sun [9] first becomes increasingly
visible, then decreasingly visible. The featured video [10]  animates images
taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter [11]  to show all
12 lunations that appear this year, 2018. A single lunation [12] describes one
full cycle of our Moon, including all of its phases [13] . A full lunation
[14]  takes about 29.5 days, just under a month ( moon-th [15] ). As each
lunation [16]  progresses, sunlight reflects from the Moon [17]  at different
angles, and so illuminates different [18]  features differently. During all of
this, of course, the Moon [19] always keeps the same face toward the Earth
[20] . What is less apparent night-to-night is that the Moon [21] 's apparent
size changes slightly, and that a slight wobble called a libration [22]
occurs as the Moon [23]  progresses along its elliptical orbit [24] .

                        Tomorrow's picture: open space

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    Authors & editors: Robert Nemiroff [36] (MTU [37] ) & Jerry Bonnell [38]
                                  (UMCP [39] )
          NASA Official:  Phillip Newman Specific rights apply [40] .
              NASA Web Privacy Policy and Important Notices [41]
              A service of: ASD [42]  at NASA [43]  / GSFC [44]
                           & Michigan Tech. U. [45]
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Site notes:
  [1] archivepix.html
  [2] https://lunar.gsfc.nasa.gov/
  [3] https://www.nasa.gov/
  [4] https://svs.gsfc.nasa.gov/
  [5] https://en.wikipedia.org/wiki/The_Blue_Danube
  [6] https://en.wikipedia.org/wiki/Johann_Strauss_...
  [7] https://solarsystem.nasa.gov/moons/earths-moo...
  [8] ap070325.html
  [9] http://en.wikipedia.org/wiki/Sun
  [10] https://svs.gsfc.nasa.gov/4604
  [11] https://lunar.gsfc.nasa.gov/about.html
  [12] http://en.wikipedia.org/wiki/Lunation
  [13] https://spaceplace.nasa.gov/review/dr-marc-ea...
  [14] http://www.inconstantmoon.com/not_phas.htm
  [15] https://www.phrases.org.uk/bulletin_board/11/...
  [16] http://scienceworld.wolfram.com/astronomy/Lun...
  [17] moon.html
  [18] ap180522.html
  [19] http://en.wikipedia.org/wiki/Moon
  [20] ap171204.html
  [21] http://www.astronomycafe.net/qadir/amoonm.htm...
  [22] http://en.wikipedia.org/wiki/Libration
  [23] ap180318.html
  [24]
http://galileoandeinstein.physics.virginia.ed...
  [25] ap180911.html
  [26] archivepix.html
  [27] lib/apsubmit2015.html
  [28] lib/aptree.html
  [29] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apo...
  [30] calendar/allyears.html
  [31] /apod.rss
  [32] lib/edlinks.html
  [33] lib/about_apod.html
  [34] http://asterisk.apod.com/discuss_apod.php?dat...
  [35] ap180913.html
  [36] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [37] http://www.phy.mtu.edu/
  [38] https://antwrp.gsfc.nasa.gov/htmltest/jbonnel...
  [39] http://www.astro.umd.edu/
  [40] lib/about_apod.html#srapply
  [41] https://www.nasa.gov/about/highlights/HP_Priv...
  [42] https://astrophysics.gsfc.nasa.gov/
  [43] https://www.nasa.gov/
  [44] https://www.nasa.gov/centers/goddard/
  [45] http://www.mtu.edu/

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