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.

                              2021 September 30
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

                         The Hydrogen Clouds of M33
               Image Credit & [3]Copyright: [4]Luca Fornaciari

   Explanation: Gorgeous spiral galaxy M33 seems to have more than its
   fair share of glowing hydrogen gas. A prominent member of the local
   group of galaxies, M33 is also known as the [5]Triangulum Galaxy and
   lies a mere 3 million light-years away. Sprawling along loose spiral
   arms that wind toward the core, M33's giant [6]HII regions are some of
   the largest known stellar nurseries, sites of the formation of
   short-lived but very massive stars. Intense ultraviolet radiation from
   the luminous massive stars ionizes the surrounding hydrogen gas and
   ultimately produces the characteristic red glow. To highlight the HII
   regions in this telescopic image, broadband data used to produce a
   color view of the galaxy were combined with narrowband data recorded
   through a [7]hydrogen-alpha filter, transmitting the light of the
   strongest [8]hydrogen emission line. Close-ups of cataloged HII regions
   appear in the sidebar insets. Use the individual reference number to
   find their location within the Triangulum Galaxy. For example, giant
   [9]HII region NGC604 is identified in an inset on the right and appears
   at position number 15. That's about 4 o'clock from galaxy center in
   [10]this portrait of M33.

                 Tomorrow's picture: ceci n'est pas une pipe
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    Authors & editors: [22]Robert Nemiroff ([23]MTU) & [24]Jerry Bonnell
                                 ([25]UMCP)
          NASA Official: Phillip Newman [26]Specific rights apply.
              [27]NASA Web Privacy Policy and Important Notices
                A service of: [28]ASD at [29]NASA / [30]GSFC
                           & [31]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2109/NebulaeTriangulumM33-1.jpg
   3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
   4. https://www.lucafornaciarifotografia.com/
   5. https://apod.nasa.gov/apod/ap191231.html
   6. https://en.wikipedia.org/wiki/H_II_region
   7. https://en.wikipedia.org/wiki/H-alpha#Filter
   8. https://en.wikipedia.org/wiki/H-alpha#/media/File:Emission_spectrum-H.svg
   9. https://hubblesite.org/contents/media/images/2003/30/1422-Image.html
  10. https://www.lucafornaciarifotografia.com/2021/09/26/astrofotografia-sulla-galassia-triangolo-m33-e-le-sue-nebulose/
  11. https://apod.nasa.gov/apod/ap210929.html
  12. https://apod.nasa.gov/apod/archivepix.html
  13. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  14. https://apod.nasa.gov/apod/lib/aptree.html
  15. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  16. https://apod.nasa.gov/apod/calendar/allyears.html
  17. https://apod.nasa.gov/apod.rss
  18. https://apod.nasa.gov/apod/lib/edlinks.html
  19. https://apod.nasa.gov/apod/lib/about_apod.html
  20. http://asterisk.apod.com/discuss_apod.php?date=210930
  21. https://apod.nasa.gov/apod/ap211001.html
  22. http://www.phy.mtu.edu/faculty/Nemiroff.html
  23. http://www.phy.mtu.edu/
  24. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  25. http://www.astro.umd.edu/
  26. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  27. https://www.nasa.gov/about/highlights/HP_Privacy.html
  28. https://astrophysics.gsfc.nasa.gov/
  29. https://www.nasa.gov/
  30. https://www.nasa.gov/centers/goddard/
  31. http://www.mtu.edu/