Astronomy Picture of the Day

   [1]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 September 26
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

                         A SWAN, an ATLAS, and Mars
                 Image Credit & [3]Copyright: [4]Adam Block

   Explanation: [5]A new visitor to the inner Solar System, comet
   [6]C/2025 R2 (SWAN) sports a long ion tail extending diagonally across
   this almost 7 degree wide telescopic field of view [7]recorded on
   September 21. A fainter fellow comet also making its inner Solar System
   debut, [8]C/2025 K1 (ATLAS), can be spotted above and left of SWAN's
   greenish coma, just visible against the background sea of stars in the
   constellation Virgo. Both new comets were only discovered in 2025 and
   are joined in this celestial frame by ruddy planet Mars (bottom), a
   more familiar wanderer in planet Earth's night skies. The [9]comets may
   appear to be in a race, nearly neck and neck in their voyage through
   the inner Solar System and around the Sun. But this comet SWAN has
   already reached its perihelion or closest approach to the Sun on
   September 12 and is now outbound along its orbit. [10]This comet ATLAS
   is still inbound though, and will make its perihelion passage on
   October 8.

                      Tomorrow's picture: light-weekend
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    Authors & editors: [22]Robert Nemiroff ([23]MTU) & [24]Jerry Bonnell
                                 ([25]UMCP)
          NASA Official: Amber Straughn [26]Specific rights apply.
            [27]NASA Web Privacy, [28]Accessibility, [29]Notices;
                A service of: [30]ASD at [31]NASA / [32]GSFC,
                         [33]NASA Science Activation
                           & [34]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2509/C2025_R2_Swan_20250921s.jpg
   3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
   4. https://www.adamblockphotos.com/
   5. https://apod.nasa.gov/apod/ap250916.html
   6. https://earthsky.org/space/new-comet-swan25b-2025/
   7. https://app.astrobin.com/i/vf43w6
   8. https://theskylive.com/c2025k1-info
   9. https://science.nasa.gov/solar-system/comets/facts/
  10. https://www.skyatnightmagazine.com/news/c-2025-k1-atlas
  11. https://apod.nasa.gov/apod/ap250925.html
  12. https://apod.nasa.gov/apod/archivepix.html
  13. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  14. https://apod.nasa.gov/apod/lib/aptree.html
  15. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  16. https://apod.nasa.gov/apod/calendar/allyears.html
  17. https://apod.com/feed.rss
  18. https://apod.nasa.gov/apod/lib/edlinks.html
  19. https://apod.nasa.gov/apod/lib/about_apod.html
  20. https://asterisk.apod.com/discuss_apod.php?date=250926
  21. https://apod.nasa.gov/apod/ap250927.html
  22. http://www.phy.mtu.edu/faculty/Nemiroff.html
  23. http://www.phy.mtu.edu/
  24. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  25. http://www.astro.umd.edu/
  26. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  27. https://www.nasa.gov/about/highlights/HP_Privacy.html
  28. https://www.nasa.gov/general/accessibility/
  29. https://www.nasa.gov/privacy/
  30. https://astrophysics.gsfc.nasa.gov/
  31. https://www.nasa.gov/
  32. https://www.nasa.gov/centers/goddard/
  33. https://science.nasa.gov/learners
  34. http://www.mtu.edu/