              APOD: 2017 November 15 - NGC 7789: Caroline's Rose

                         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
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                               2017 November 15
                                      [2]
                          NGC 7789: Caroline's Rose
            Image Credit & Copyright [3] : Guillaume Seigneure [4]

Explanation: Found among the rich starfields of the Milky Way, star cluster
NGC 7789 [5]  lies about 8,000 light-years away toward the constellation
Cassiopeia. A late 18th century deep sky discovery [6]  of astronomer Caroline
Lucretia Herschel [7] , the cluster is also known as Caroline's Rose. Its
flowery visual appearance [8] in small telescopes is created by the cluster's
nestled complex of stars and voids. Now estimated to be 1.6 billion years
young, the galactic or open cluster of stars also shows its age. All the stars
in the cluster were likely born at the same time, but the brighter and more
massive ones have more rapidly exhausted the hydrogen fuel in their cores.
These have evolved from main sequence [9] stars like the Sun into the many red
giant stars shown with a yellowish cast in this lovely color composite. Using
measured color and brightness [10] , astronomers can model the mass and hence
the age of the cluster stars just starting to "turn off" the main sequence and
become red giants [11] . Over 50 light-years across, Caroline's Rose [12]
spans about half a degree (the angular size of the Moon) near the center of
the wide-field telescopic image [13] .

                   Tomorrow's picture: pixels in space [14]

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Site notes:
  [1] archivepix.html
  [2] image/1711/NGC7789Rose_Seigneuret2048.jpg
  [3] lib/about_apod.html#srapply
  [4] https://www.flickr.com/photos/drgkill/
  [5] http://messier.seds.org/xtra/ngc/n7789.html
  [6] http://www.skyandtelescope.com/observing/ Caroline_Herschel_Objects.html
  [7] http://www-history.mcs.st-and.ac.uk/Biographies/ Herschel_Caroline.html
  [8]  http://www.asod.info/?p=6548
  [9] http://en.wikipedia.org/wiki/Main_sequence
  [10] ap010223.html
  [11] ap110408.html
  [12] http://adsbit.harvard.edu//full/1848MNRAS...8...64./ 0000064.000.html
  [13] https://www.flickr.com/photos/drgkill/37408484425/
  [14] ap171116.html
  [15] ap171114.html
  [16] archivepix.html
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  [26] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [27] http://www.phy.mtu.edu/
  [28] http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
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