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.

                               2020 October 16

                          Planetary Nebula Abell 78
                   Image Credit & Copyright: Bernhard Hubl

   Explanation: Planetary nebula Abell 78 stands out in this colorful
   telescopic skyscape. In fact the colors of the spiky Milky Way stars
   depend on their surface temperatures, both cooler (yellowish) and
   hotter (bluish) than the Sun. But Abell 78 shines by the characteristic
   emission of ionized atoms in the tenuous shroud of material shrugged
   off from an intensely hot central star. The atoms are ionized, their
   electrons stripped away, by the central star's energetic but otherwise
   invisible ultraviolet light. The visible blue-green glow of loops and
   filaments in the nebula's central region corresponds to emission from
   doubly ionized oxygen atoms, surrounded by strong red emission from
   ionized hydrogen. Some 5,000 light-years distant toward the
   constellation Cygnus, Abell 78 is about three light-years across. A
   planetary nebula like Abell 78 represents a very brief final phase in
   stellar evolution that our own Sun will experience ... in about 5
   billion years.

                      Tomorrow's picture: light-weekend
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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