                        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 July 21

                      Colors: Ring Nebula versus Stars
                Image Credit: Robert Vanderbei (Princeton U.)

   Explanation: What if you could see, separately, all the colors of the
   Ring? And of the surrounding stars? There's technology for that. The
   featured image shows the Ring Nebula (M57) and nearby stars through
   such technology: in this case, a prism-like diffraction grating. The
   Ring Nebula is seen only a few times because it emits light, primarily,
   in only a few colors. The two brightest emitted colors are hydrogen
   (red) and oxygen (blue), appearing as nearly overlapping images to the
   left of the image center. The image just to the right of center is the
   color-combined icon normally seen. Stars, on the other hand, emit most
   of their light in colors all across the visible spectrum. These colors,
   combined, make a nearly continuous streak -- which is why stars appear
   accompanied by multicolored bars. Breaking object light up into colors
   is scientifically useful because it can reveal the elements that
   compose that object, how fast that object is moving, and how distant
   that object is.

                       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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                             & Michigan Tech. U.


