                        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 May 5

                          STEVE over Copper Harbor
                Image Credit & Copyright: MaryBeth Kiczenski

   Explanation: What creates STEVEs? Strong Thermal Emission Velocity
   Enhancements (STEVEs) have likely been seen since antiquity, but only
   in the past five years has it been realized that their colors and
   shapes make them different from auroras. Seen as single bright streaks
   of pink and purple, the origin of STEVEs remain an active topic of
   research. STEVEs may be related to subauroral ion drifts (SAIDs), a
   supersonic river of hot atmospheric ions. For reasons currently
   unknown, STEVEs are frequently accompanied by green "picket-fence"
   auroras. The featured STEVE image is a combination of foreground and
   background exposures taken consecutively in mid-March from Copper
   Harbor, Michigan, USA. This bright STEVE lasted several minutes,
   spanned from horizon to horizon, and appeared in between times of
   normal auroras.

                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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