                        Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2021 October 21

                      SH2-308: The Dolphin-Head Nebula
                   Image Credit & Copyright: Nik Szymanek

   Explanation: Blown by fast winds from a hot, massive star, this cosmic
   bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,000
   light-years away toward the constellation of the Big Dog (Canis Major)
   and covers slightly more of the sky than a Full Moon. That corresponds
   to a diameter of 60 light-years at its estimated distance. The massive
   star that created the bubble, a Wolf-Rayet star, is the bright one near
   the center of the nebula. Wolf-Rayet stars have over 20 times the mass
   of the Sun and are thought to be in a brief, pre-supernova phase of
   massive star evolution. Fast winds from this Wolf-Rayet star create the
   bubble-shaped nebula as they sweep up slower moving material from an
   earlier phase of evolution. The windblown nebula has an age of about
   70,000 years. Relatively faint emission captured by narrowband filters
   in the deep image is dominated by the glow of ionized oxygen atoms
   mapped to a blue hue. Presenting a mostly harmless outline, SH2-308 is
   also known as The Dolphin-head Nebula.

                      Tomorrow's picture: it's a comet
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