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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.   
      
                                 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   
        __________________________________________________________________   
      
          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.   
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