                        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 April 21
     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: ESA/Webb, NASA & CSA, 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 galaxy
   collides with a larger galaxy and ends up in the center. But in the
   featured image, something more rare is going on. Here, the central
   light-colored elliptical galaxy is much closer than the blue and
   red-colored spiral galaxy that surrounds it. This can happen when near
   and far galaxies are exactly aligned, causing the gravity of the near
   galaxy to pull the light from the far galaxy around it in an effect
   called gravitational lensing. The featured galaxy double was taken by
   the Webb Space Telescope and shows a complete Einstein ring, with great
   detail visible for both galaxies. Galaxy lenses like this can reveal
   new information about the mass distribution of the foreground lens and
   the light distribution of the background source.

                     Tomorrow's picture: terminator moon
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
                  NASA Web Privacy, Accessibility, Notices;
                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

