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.

                                2019 March 28
                                      [2]
                            The Gaia Stars of M15
Image Credit: Robert Vanderbei (Princeton University) [3] , ESA [4] , Gaia [5]
                                  , DPAC [6]

Explanation: Messier 15 [7] is a 13 billion year old relic of the early
formative years of our galaxy, one of about 170 globular star clusters that
still roam the halo of the Milky Way. About 200 light-years [8]  in diameter,
it lies about 35,000 light years [9]  away toward the constellation Pegasus.
But this realistic looking view of the ancient globular star cluster is not a
photograph. Instead it's an animated gif image constructed from remarkably
precise individual measurements of star positions, brightness, and color. The
astronomically rich data set used was made by the sky-scanning [10] Gaia
satellite [11]  which also determined parallax [12]  distances for 1.3 billion
Milky Way stars. In the animated gif, twinkling stars are M15's identified RR
Lyrae stars. Plentiful in M15, RR Lyrae stars [13] are evolved pulsating
variable stars whose brightness and pulsation period, typically less than a
day, are related.

                 Tomorrow's picture: hat the size of a galaxy

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    Authors & editors: Robert Nemiroff [25] (MTU [26] ) & Jerry Bonnell [27]
                                  (UMCP [28] )
          NASA Official:  Phillip Newman Specific rights apply [29] .
              NASA Web Privacy Policy and Important Notices [30]
              A service of: ASD [31]  at NASA [32]  / GSFC [33]
                           & Michigan Tech. U. [34]
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Site notes:
  [1] archivepix.html
  [2] image/1903/M15_Gaia_stars.gif
  [3] https://vanderbei.princeton.edu/
  [4] http://www.esa.int/
  [5] https://www.cosmos.esa.int/web/gaia/home
  [6] https://www.cosmos.esa.int/web/gaia/dpac/cons...
  [7] ap181017.html
  [8] http://hubblesite.org/news_release/news/2002-...
  [9] http://chandra.harvard.edu/photo/cosmic_dista...
  [10] https://www.youtube.com/watch?v=BnFyzZGWuYs
  [11] https://www.cosmos.esa.int/web/gaia/data-rele...
  [12] https://www.esa.int/Our_Activities/Space_Scie... Parallax
  [13] https://en.wikipedia.org/wiki/RR_Lyrae_variab...
  [14] ap190327.html
  [15] archivepix.html
  [16] lib/apsubmit2015.html
  [17] lib/aptree.html
  [18] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apo...
  [19] calendar/allyears.html
  [20] /apod.rss
  [21] lib/edlinks.html
  [22] lib/about_apod.html
  [23] http://asterisk.apod.com/discuss_apod.php?dat...
  [24] ap190329.html
  [25] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [26] http://www.phy.mtu.edu/
  [27] https://antwrp.gsfc.nasa.gov/htmltest/jbonnel...
  [28] http://www.astro.umd.edu/
  [29] lib/about_apod.html#srapply
  [30] https://www.nasa.gov/about/highlights/HP_Priv...
  [31] https://astrophysics.gsfc.nasa.gov/
  [32] https://www.nasa.gov/
  [33] https://www.nasa.gov/centers/goddard/
  [34] http://www.mtu.edu/

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