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                        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.

                                2025 August 4
   The Andromeda Galaxy is shown just right of center, while some unusual
      blue arcs appear to its left. Please see the explanation for more
                            detailed information.

                         Blue Arcs Toward Andromeda
                    Image Credit & Copyright: Ogle et al.

   Explanation: What are these gigantic blue arcs near the Andromeda
   Galaxy (M31)? Discovered in 2022 by amateur astronomers, the faint arcs
   -- dubbed SDSO 1 -- span nearly the same angular size as M31 itself. At
   first, their origin was a mystery: are they actually near the Andromeda
   Galaxy, or alternatively near to our Sun? Now, over 550 hours of
   combined exposure and a collaboration between amateur and professional
   astronomers has revealed strong evidence for their true nature: SDSO 1
   is not intergalactic, but a new class of planetary nebula within our
   galaxy. Dubbed a Ghost Planetary Nebula (GPN), SDSO 1 is the first
   recognized member of a new subclass of faded planetary nebulas, along
   with seven others also recently identified. Shown in blue are extremely
   faint oxygen emission from the shock waves, while the surrounding red
   is a hydrogen-emitting trail that indicates the GPN's age.

                 Tomorrow's picture: complex stellar jumble
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

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