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 __________________________________________________________________ [11]< | [12]Archive | [13]Submissions | [14]Index | [15]Search | [16]Calendar | [17]RSS | [18]Education | [19]About APOD | [20]Discuss | [21]> __________________________________________________________________ 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/