                        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 January 28
    A foreground grass field is shown below a distant field of stars. On
    the grass field are some trees. Dwarfing the trees, in the sky, is a
    comet with a long tail. Please see the explanation for more detailed
                                information.

                         Comet G3 ATLAS over Uruguay
                 Image Credit & Copyright: Mauricio Salazar

   Explanation: Comets can be huge. When far from the Sun, a comet's size
   usually refers to its hard nucleus of ice and rock, which typically
   spans a few kilometers -- smaller than even a small moon. When nearing
   the Sun, however, this nucleus can eject dust and gas and leave a thin
   tail that can spread to an enormous length -- even greater than the
   distance between the Earth and the Sun. Pictured, C/2024 G3 (ATLAS)
   sports a tail of sunlight-reflecting dust and glowing gas that spans
   several times the apparent size of a full moon, appearing even larger
   on long duration camera images than to the unaided eye. The featured
   image shows impressive Comet ATLAS over trees and a grass field in
   Sierras de Mahoma, San Jose, Uruguay about a week ago. After being
   prominent in the sunset skies of Earth's southern hemisphere, Comet G3
   ATLAS is now fading as it moves away from the Sun, making its
   impressive tails increasingly hard to see.

                          Gallery: Comet ATLAS (G3)
                      Tomorrow's picture: star circles
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