                        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 November 23
     A diagram is shown depicting various parts of the universe that are
    observable. In the middle are the parts closest to Earth, and around
   the far edges are parts furthest from Earth. Planets, galaxies, and the
      CMB are illustrated. Please see the explanation for more detailed
                                information.

                           The Observable Universe
       Illustration Credit & Licence: Wikipedia, Pablo Carlos Budassi

   Explanation: How far can you see? Everything you can see, and
   everything you could possibly see, right now, assuming your eyes could
   detect all types of radiations around you -- is the observable
   universe. In light, the farthest we can see comes from the cosmic
   microwave background, a time 13.8 billion years ago when the universe
   was opaque like thick fog. Some neutrinos and gravitational waves that
   surround us come from even farther out, but humanity does not yet have
   the technology to detect them. The featured image illustrates the
   observable universe on an increasingly compact scale, with the Earth
   and Sun at the center surrounded by our Solar System, nearby stars,
   nearby galaxies, distant galaxies, filaments of early matter, and the
   cosmic microwave background. Cosmologists typically assume that our
   observable universe is just the nearby part of a greater entity known
   as "the universe" where the same physics applies. However, there are
   several lines of popular but speculative reasoning that assert that
   even our universe is part of a greater multiverse where either
   different physical constants occur, different physical laws apply,
   higher dimensions operate, or slightly different-by-chance versions of
   our standard universe exist.

           Explore the Observable Universe: Random APOD Generator
                   Tomorrow's picture: stellar shell game
     __________________________________________________________________

       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.

