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.

                               2020 October 14

                     The Colorful Clouds of Rho Ophiuchi
                 Image Credit & Copyright: Amir H. Abolfath

   Explanation: The many spectacular colors of the Rho Ophiuchi
   (oh'-fee-yu-kee) clouds highlight the many processes that occur there.
   The blue regions shine primarily by reflected light. Blue light from
   the Rho Ophiuchi star system and nearby stars reflects more efficiently
   off this portion of the nebula than red light. The Earth's daytime sky
   appears blue for the same reason. The red and yellow regions shine
   primarily because of emission from the nebula's atomic and molecular
   gas. Light from nearby blue stars - more energetic than the bright star
   Antares - knocks electrons away from the gas, which then shines when
   the electrons recombine with the gas. The dark brown regions are caused
   by dust grains - born in young stellar atmospheres - which effectively
   block light emitted behind them. The Rho Ophiuchi star clouds, well in
   front of the globular cluster M4 visible here on the upper right, are
   even more colorful than humans can see - the clouds emits light in
   every wavelength band from the radio to the gamma-ray.

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