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 April 21
   [2]What looks like a single spiral galaxy is shown with a white center
      surrounded by inner blue arms and outer red arms. Please see the
                 explanation for more detailed information.

                       Galaxy Lenses Galaxy from Webb
          Image Credit: [3]ESA/Webb, [4]NASA & [5]CSA, [6]G. Mahler

   Explanation: Is this one galaxy or two? Although it looks like one, the
   answer is two. One path to this happening is when a small [7]galaxy
   collides with a larger galaxy and [8]ends up in the center. But in the
   [9]featured image, something [10]more rare is going on. Here, the
   central light-colored [11]elliptical galaxy is much closer than the
   blue and red-colored [12]spiral galaxy that surrounds it. This can
   happen when near and far galaxies are [13]exactly aligned, causing the
   gravity of the near galaxy to pull the light from the far galaxy around
   it in an effect called [14]gravitational lensing. The [15]featured
   galaxy double was taken by the [16]Webb Space Telescope and shows a
   complete [17]Einstein ring, with great detail visible for both
   galaxies. Galaxy [18]lenses like this can reveal new information about
   the [19]mass distribution of the foreground lens and the [20]light
   distribution of the background source.

                     Tomorrow's picture: terminator moon
     __________________________________________________________________

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     __________________________________________________________________

    Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell
                                 ([35]UMCP)
          NASA Official: Amber Straughn [36]Specific rights apply.
            [37]NASA Web Privacy, [38]Accessibility, [39]Notices;
                A service of: [40]ASD at [41]NASA / [42]GSFC,
                         [43]NASA Science Activation
                           & [44]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2504/GalaxiesLens_Webb_1146.jpg
   3. https://esawebb.org/
   4. https://www.nasa.gov/
   5. https://www.asc-csa.gc.ca/eng/
   6. https://orbi.uliege.be/profile?uid=p288273
   7. https://spaceplace.nasa.gov/galaxy/en/
   8. https://apod.nasa.gov/apod/ap201018.html
   9. https://www.esa.int/ESA_Multimedia/Images/2025/03/Webb_spies_a_spiral_through_a_cosmic_lens
  10. https://www.reddit.com/r/aww/comments/2jqsdk/the_omg_cat/#lightbox
  11. https://science.nasa.gov/universe/galaxies/types/#elliptical-galaxies
  12. https://science.nasa.gov/universe/galaxies/types/#spiral-galaxies
  13. https://science.nasa.gov/wp-content/uploads/2023/04/stsci-h-p2005b-f-4096x2160-1-jpg.webp
  14. https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/hubble-gravitational-lenses/
  15. https://esawebb.org/images/potm2503a/
  16. https://webbtelescope.org/home
  17. https://apod.nasa.gov/apod/ap160420.html
  18. https://apod.nasa.gov/apod/ap220705.html
  19. https://science.nasa.gov/mission/hubble/science/science-highlights/shining-a-light-on-dark-matter/
  20. https://www.ucdavis.edu/news/newly-discovered-gravitational-lenses-could-reveal-ancient-galaxies-and-nature-dark-matter
  21. https://apod.nasa.gov/apod/ap250420.html
  22. https://apod.nasa.gov/apod/archivepix.html
  23. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  24. https://apod.nasa.gov/apod/lib/aptree.html
  25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  26. https://apod.nasa.gov/apod/calendar/allyears.html
  27. https://apod.com/feed.rss
  28. https://apod.nasa.gov/apod/lib/edlinks.html
  29. https://apod.nasa.gov/apod/lib/about_apod.html
  30. https://asterisk.apod.com/discuss_apod.php?date=250421
  31. https://apod.nasa.gov/apod/ap250422.html
  32. http://www.phy.mtu.edu/faculty/Nemiroff.html
  33. http://www.phy.mtu.edu/
  34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  35. http://www.astro.umd.edu/
  36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  37. https://www.nasa.gov/about/highlights/HP_Privacy.html
  38. https://www.nasa.gov/general/accessibility/
  39. https://www.nasa.gov/privacy/
  40. https://astrophysics.gsfc.nasa.gov/
  41. https://www.nasa.gov/
  42. https://www.nasa.gov/centers/goddard/
  43. https://science.nasa.gov/learners
  44. http://www.mtu.edu/