                        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 November 3

                       The Horsehead and Flame Nebulas
                   Image Credit & Copyright: Wissam Ayoub

   Explanation: The Horsehead Nebula is one of the most famous nebulae on
   the sky. It is visible as the dark indentation to the orange emission
   nebula at the far right of the featured picture. The horse-head feature
   is dark because it is really an opaque dust cloud that lies in front of
   the bright emission nebula. Like clouds in Earth's atmosphere, this
   cosmic cloud has assumed a recognizable shape by chance. After many
   thousands of years, the internal motions of the cloud will surely alter
   its appearance. The emission nebula's orange color is caused by
   electrons recombining with protons to form hydrogen atoms. Toward the
   lower left of the image is the Flame Nebula, an orange-tinged nebula
   that also contains intricate filaments of dark dust. Two prominent
   reflection nebulas are visible: round IC 432 on the far left, and blue
   NGC 2023 just to the lower left of the Horsehead nebula. Each glows
   primarily by reflecting the light of their central star.

   Discovery + Outreach: Graduate student research position open for APOD
                       Tomorrow's picture: open space
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