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 2
      [2]A starfield is shown with bright and dark nebulae of different
       shapes and colors. Please see the explanation for more detailed
                                information.

                       The Horsehead and Flame Nebulas
                  Image Credit & Copyright: [3]Daniel Stern

   Explanation: The [4]Horsehead Nebula is one of the most famous nebulae
   on the sky. It is visible as the dark indentation to the orange
   [5]emission nebula at the far right of the [6]featured picture. The
   [7]horse-head feature is dark because it is really an opaque [8]dust
   cloud that lies in front of the bright [9]emission nebula. Like clouds
   in [10]Earth's atmosphere, this cosmic cloud has assumed a
   [11]recognizable shape by chance. After [12]many thousands of years,
   the internal motions of the cloud will surely alter its appearance. The
   emission [13]nebula's orange color is caused by [14]electrons
   recombining with [15]protons to form [16]hydrogen atoms. Toward the
   lower left of the image is the [17]Flame Nebula, an orange-tinged
   nebula that also contains intricate filaments of dark dust.

                        Tomorrow's picture: star jet
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    Authors & editors: [29]Robert Nemiroff ([30]MTU) & [31]Jerry Bonnell
                                 ([32]UMCP)
          NASA Official: Amber Straughn [33]Specific rights apply.
            [34]NASA Web Privacy, [35]Accessibility, [36]Notices;
                A service of: [37]ASD at [38]NASA / [39]GSFC,
                         [40]NASA Science Activation
                           & [41]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2509/OrionHorseHead_Stern_5842.jpg
   3. https://www.instagram.com/messierchaser/
   4. https://en.wikipedia.org/wiki/Horsehead_nebula
   5. https://en.wikipedia.org/wiki/Emission_nebula
   6. https://www.instagram.com/p/DFRDLZ0uUoF/
   7. https://apod.nasa.gov/apod/ap140728.html
   8. https://apod.nasa.gov/apod/ap030706.html
   9. https://astronomy.swin.edu.au/cosmos/E/emission+nebula
  10. https://www.nasa.gov/image-article/earths-atmospheric-layers-3/
  11. https://apod.nasa.gov/apod/ap240114.html
  12. https://cdn.shopify.com/s/files/1/0272/4770/6214/articles/do-cats-get-bored-800x533.jpg
  13. https://apod.nasa.gov/apod/ap061015.html
  14. https://history.aip.org/exhibits/electron/
  15. https://home.cern/news/news/physics/proton-century
  16. https://periodic.lanl.gov/1.shtml
  17. https://apod.nasa.gov/apod/ap210412.html
  18. https://apod.nasa.gov/apod/ap250901.html
  19. https://apod.nasa.gov/apod/archivepix.html
  20. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  21. https://apod.nasa.gov/apod/lib/aptree.html
  22. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  23. https://apod.nasa.gov/apod/calendar/allyears.html
  24. https://apod.com/feed.rss
  25. https://apod.nasa.gov/apod/lib/edlinks.html
  26. https://apod.nasa.gov/apod/lib/about_apod.html
  27. https://asterisk.apod.com/discuss_apod.php?date=250902
  28. https://apod.nasa.gov/apod/ap250903.html
  29. http://www.phy.mtu.edu/faculty/Nemiroff.html
  30. http://www.phy.mtu.edu/
  31. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  32. http://www.astro.umd.edu/
  33. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  34. https://www.nasa.gov/about/highlights/HP_Privacy.html
  35. https://www.nasa.gov/general/accessibility/
  36. https://www.nasa.gov/privacy/
  37. https://astrophysics.gsfc.nasa.gov/
  38. https://www.nasa.gov/
  39. https://www.nasa.gov/centers/goddard/
  40. https://science.nasa.gov/learners
  41. http://www.mtu.edu/