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.

                              2019 September 29

              MyCn 18: The Engraved Hourglass Planetary Nebula
     Image Credit: NASA, ESA, Hubble; Processing & License: Judy Schmidt

   Explanation: Do you see the hourglass shape -- or does it see you? If
   you can picture it, the rings of MyCn 18 trace the outline of an
   hourglass -- although one with an unusual eye in its center. Either
   way, the sands of time are running out for the central star of this
   hourglass-shaped planetary nebula. With its nuclear fuel exhausted,
   this brief, spectacular, closing phase of a Sun-like star's life occurs
   as its outer layers are ejected - its core becoming a cooling, fading
   white dwarf. In 1995, astronomers used the Hubble Space Telescope (HST)
   to make a series of images of planetary nebulae, including the one
   featured here. Pictured, delicate rings of colorful glowing gas
   (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous
   walls of the hourglass. The unprecedented sharpness of the Hubble
   images has revealed surprising details of the nebula ejection process
   that are helping to resolve the outstanding mysteries of the complex
   shapes and symmetries of planetary nebulas like MyCn 18.

                       Tomorrow's picture: orion treed
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

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