                        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.

                              2021 November 23

                        The Sun in X-rays from NuSTAR
                       Image Credit: NASA, NuSTAR, SDO

   Explanation: Why are the regions above sunspots so hot? Sunspots
   themselves are a bit cooler than the surrounding solar surface because
   the magnetic fields that create them reduce convective heating. It is
   therefore unusual that regions overhead -- even much higher up in the
   Sun's corona -- can be hundreds of times hotter. To help find the
   cause, NASA directed the Earth-orbiting Nuclear Spectroscopic Telescope
   Array (NuSTAR) satellite to point its very sensitive X-ray telescope at
   the Sun. Featured here is the Sun in ultraviolet light, shown in a red
   hue as taken by the orbiting Solar Dynamics Observatory (SDO).
   Superimposed in false-colored green and blue is emission above sunspots
   detected by NuSTAR in different bands of high-energy X-rays,
   highlighting regions of extremely high temperature. Clues about the
   Sun's atmospheric heating mechanisms come from NuSTAR images like this
   and shed light on solar nanoflares and microflares as brief bursts of
   energy that may drive the unusual heating.

                     Tomorrow's picture: stellar sisters
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.

