                        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.

                                2023 March 22
   The Andromeda Galaxy is shown in great detail. Red nebulas, blue stars,
      and dark dust are all seen in a swirl around the galaxy's bright
      center. Please see the explanation for more detailed information.

                          M31: The Andromeda Galaxy
                 Image Credit & Copyright: Abdullah Al-Harbi

   Explanation: How far can you see? The most distant object easily
   visible to the unaided eye is M31, the great Andromeda Galaxy, over two
   million light-years away. Without a telescope, even this immense spiral
   galaxy appears as an unremarkable, faint, nebulous cloud in the
   constellation Andromeda. But a bright white nucleus, dark winding dust
   lanes, luminous blue spiral arms, and bright red emission nebulas are
   recorded in this stunning fifteen-hour telescopic digital mosaic of our
   closest major galactic neighbor. But how do we know this spiral nebula
   is really so far away? This question was central to the famous
   Shapley-Curtis debate of 1920. M31's great distance was determined in
   the 1920s by observations that resolved individual stars that changed
   their brightness in a way that gave up their true distance. The result
   proved that Andromeda is just like our Milky Way Galaxy -- a conclusion
   making the rest of the universe much more vast than had ever been
   previously imagined.

                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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