                        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.

                              2021 September 30

                         The Hydrogen Clouds of M33
                  Image Credit & Copyright: 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 Triangulum Galaxy and lies
   a mere 3 million light-years away. Sprawling along loose spiral arms
   that wind toward the core, M33's giant 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
   hydrogen-alpha filter, transmitting the light of the strongest 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 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 this portrait of M33.

                 Tomorrow's picture: ceci n'est pas une pipe
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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