                        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.

                              2025 December 26

                               3I/ATLAS Flyby
                   Image Credit & Copyright: Dan Bartlett

   Explanation: Attention grabbing interstellar visitor 3I/ATLAS made its
   not-so-close flyby of our fair planet on December 19 at a distance of
   1.8 astronomical units. That's about 900 light-seconds. Still, this
   deep exposure captures the comet from another star system as it gently
   swept across a faint background of stars in the constellation Leo about
   4 days earlier, on the night of December 15. Though faint, colors
   emphasized in the image data, show off the comet's yellowish dust tail
   and bluish ion tail along with a greenish tinged coma. And even while
   scrutinized by arrays of telescopes and spacecraft from planet Earth,
   3I ATLAS is headed out of the Solar System. It's presently moving
   outward along a hyperbolic trajectory at about 64 kilometers per second
   relative to the Sun, too fast to be bound the Sun's gravity.

                    Tomorrow's picture: Apollo's Moonship
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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                             & Michigan Tech. U.

