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 November 23
   [2]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 & [3]Licence: [4]Wikipedia, [5]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 [6]observable
   universe. In light, the farthest we can see comes from the [7]cosmic
   microwave background, a time [8]13.8 billion years ago when the
   universe was opaque like thick fog. Some [9]neutrinos and
   [10]gravitational waves that surround us come from even farther out,
   but humanity does not yet have the technology to detect them. The
   [11]featured image illustrates the observable universe on an
   [12]increasingly compact scale, with the [13]Earth and [14]Sun at the
   center surrounded by [15]our Solar System, [16]nearby stars, [17]nearby
   galaxies, [18]distant galaxies, [19]filaments of early matter, and the
   [20]cosmic microwave background. Cosmologists typically assume that our
   observable [21]universe is just the nearby part of a [22]greater entity
   known as "the universe" where the same physics applies. However, there
   are several lines of popular but speculative reasoning that [23]assert
   that even our universe is part of a [24]greater multiverse where either
   different physical constants occur, [25]different physical laws apply,
   [26]higher dimensions operate, or slightly [27]different-by-chance
   versions of our standard universe exist.

         Explore the Observable Universe: [28]Random APOD Generator
                   Tomorrow's picture: stellar shell game
     __________________________________________________________________

      [29]< | [30]Archive | [31]Submissions | [32]Index | [33]Search |
   [34]Calendar | [35]RSS | [36]Education | [37]About APOD | [38]Discuss |
                                    [39]>
     __________________________________________________________________

    Authors & editors: [40]Robert Nemiroff ([41]MTU) & [42]Jerry Bonnell
                                 ([43]UMCP)
          NASA Official: Amber Straughn [44]Specific rights apply.
            [45]NASA Web Privacy, [46]Accessibility, [47]Notices;
                A service of: [48]ASD at [49]NASA / [50]GSFC,
                         [51]NASA Science Activation
                           & [52]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2511/ObsUni_WikipediaPablo_2100.jpg
   3. https://creativecommons.org/licenses/by-sa/3.0/
   4. https://en.wikipedia.org/wiki/Observable_universe#/media/File:Observable_universe_logarithmic_illustration.png
   5. https://commons.wikimedia.org/wiki/User:Unmismoobjetivo
   6. https://en.wikipedia.org/wiki/Observable_universe
   7. https://wmap.gsfc.nasa.gov/universe/bb_tests_cmb.html
   8. https://en.wikipedia.org/wiki/Age_of_the_universe
   9. https://icecube.wisc.edu/info/neutrinos
  10. https://www.ligo.caltech.edu/page/what-are-gw
  11. https://en.wikipedia.org/wiki/Observable_universe#/media/File:Observable_universe_logarithmic_illustration.png
  12. https://en.wikipedia.org/wiki/Logarithmic_scale
  13. https://science.nasa.gov/earth/
  14. https://science.nasa.gov/sun/facts/
  15. https://science.nasa.gov/solar-system/solar-system-facts/
  16. http://www.atlasoftheuniverse.com/12lys.html
  17. https://apod.nasa.gov/apod/ap110614.html
  18. https://apod.nasa.gov/apod/ap250302.html
  19. https://apod.nasa.gov/apod/ap231231.html
  20. https://apod.nasa.gov/apod/ap180722.html
  21. https://science.nasa.gov/astrophysics/science-questions/how-do-matter-energy-space-and-time-behave-under-the-extraordinarily-diverse-conditions-of-the-cosmos/
  22. https://www.reddit.com/r/aww/comments/2jsvru/super_cat/#lightbox
  23. http://asterisk.apod.com/viewtopic.php?f=39&t=21958
  24. https://en.wikipedia.org/wiki/Multiverse
  25. https://medium.com/starts-with-a-bang/ask-ethan-96-is-the-multiverse-science-ecceb24fa2af
  26. http://www.pbs.org/wgbh/nova/blogs/physics/2014/04/how-many-dimensions-does-the-universe-really-have/
  27. https://apod.nasa.gov/apod/ap170401.html
  28. https://apod.nasa.gov/apod/random_apod.html
  29. https://apod.nasa.gov/apod/ap251122.html
  30. https://apod.nasa.gov/apod/archivepix.html
  31. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  32. https://apod.nasa.gov/apod/lib/aptree.html
  33. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  34. https://apod.nasa.gov/apod/calendar/allyears.html
  35. https://apod.com/feed.rss
  36. https://apod.nasa.gov/apod/lib/edlinks.html
  37. https://apod.nasa.gov/apod/lib/about_apod.html
  38. https://asterisk.apod.com/discuss_apod.php?date=251123
  39. https://apod.nasa.gov/apod/ap251124.html
  40. http://www.phy.mtu.edu/faculty/Nemiroff.html
  41. http://www.phy.mtu.edu/
  42. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  43. http://www.astro.umd.edu/
  44. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  45. https://www.nasa.gov/about/highlights/HP_Privacy.html
  46. https://www.nasa.gov/general/accessibility/
  47. https://www.nasa.gov/privacy/
  48. https://astrophysics.gsfc.nasa.gov/
  49. https://www.nasa.gov/
  50. https://www.nasa.gov/centers/goddard/
  51. https://science.nasa.gov/learners
  52. http://www.mtu.edu/