                        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 March 14

                      A Flag Shaped Aurora over Sweden
                   Image Credit & Copyright: Mia Stålnacke

   Explanation: It appeared, momentarily, like a 50-km tall banded flag.
   In mid-March of 2015, an energetic Coronal Mass Ejection directed
   toward a clear magnetic channel to Earth led to one of the more intense
   geomagnetic storms of recent years. A visual result was wide spread
   auroras being seen over many countries near Earth's magnetic poles.
   Captured over Kiruna, Sweden, the image features an unusually straight
   auroral curtain with the green color emitted low in the Earth's
   atmosphere, and red many kilometers higher up. It is unclear where the
   rare purple aurora originates, but it might involve an unusual blue
   aurora at an even lower altitude than the green, seen superposed with a
   much higher red. Now past Solar Minimum, colorful nights of auroras
   over Earth are likely to increase.

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