                        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.

                              2023 November 21
     A nebula consisting of blue and red wisps starts thin at the image
     bottom but expands into a triangle at the image top. Please see the
                 explanation for more detailed information.

                          Fleming's Triangular Wisp
                 Image Credit & Copyright: Cristiano Gualco

   Explanation: These chaotic and tangled filaments of shocked, glowing
   gas are spread across planet Earth's sky toward the constellation of
   Cygnus as part of the Veil Nebula. The Veil Nebula itself is a large
   supernova remnant, an expanding cloud born of the death explosion of a
   massive star. Light from the original supernova explosion likely
   reached Earth over 5,000 years ago. The glowing filaments are really
   more like long ripples in a sheet seen almost edge on, remarkably well
   separated into the glow of ionized hydrogen atoms shown in red and
   oxygen in blue hues. Also known as the Cygnus Loop and cataloged as NGC
   6979, the Veil Nebula now spans about 6 times the diameter of the full
   Moon. The length of the wisp corresponds to about 30 light years, given
   its estimated distance of 2,400 light years. Often identified as
   Pickering's Triangle for a director of Harvard College Observatory, it
   is perhaps better named for its discoverer, astronomer Williamina
   Fleming, as Fleming's Triangular Wisp.

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