                        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.

                              2026 September 8
     A dark field has a bright circular disk near the center. Around the
     center of this disk are bands. One of the bands appear particularly
   geometric and appears to have 10 sides. Please see the explanation for
                         more detailed information.

                 Hubble: Decagon Around Saturn's South Pole
   Image Credit: NASA, ESA, STScI, HST; A. Sánchez-Lavega (UPV), A. Simon
      (NASA-GSFC), M. Wong (UC Berkeley); Processing: A. Pagan (STScI)

   Explanation: Why are Saturn’s poles geometric? Saturn’s North Pole has
   been known to be surrounded by a hexagonal (6 sides) cloud since
   discovery in 1987 in data taken by NASA’s Voyager spacecrafts, which
   quickly flew past the ringed world in the early 1980s. Now, recent
   observations of Saturn by the Hubble Space Telescope reveal a slightly
   different geometric cloud pattern around the South Pole: a decagon (10
   sides). The geometric boundaries are possibly caused by waves when the
   fast-moving gas away from the poles interacts with slower-moving gas
   closer to the poles. In the featured image composite by the Hubble
   taken last year, the South Pole of Saturn is marked by an X and
   surrounded by bands of circulating clouds. The decagon appears most
   prominent in the dark inner regions. The northern hexagon has proven
   stable for over 40 years, while the stability of the southern decagon
   will surely remain a topic of research.

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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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