                        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 October 12

                          Fireball over Lake Louise
                      Image Credit & Copyright: Hao Qin

   Explanation: What makes a meteor a fireball? First of all, everyone
   agrees that a fireball is an exceptionally bright meteor. Past that,
   the International Astronomical Union defines a fireball as a meteor
   brighter than apparent magnitude -4, which corresponds (roughly) to
   being brighter than any planet -- as well as bright enough to cast a
   human-noticeable shadow. Pictured, an astrophotographer taking a
   long-duration sky image captured by accident the brightest meteor he
   had ever seen. Clearly a fireball, the disintegrating space-rock
   created a trail so bright it turned night into day for about two
   seconds earlier this month. The fireball has been artificially dimmed
   in the featured image to bring up foreground Lake Louise in Alberta,
   Canada. Although fireballs are rare, many people have been lucky enough
   to see them. If you see a fireball, you can report it. If more than one
   person recorded an image, the fireball might be traceable back to the
   Solar System body from which it was ejected.

                      Tomorrow's picture: big question
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