                        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 December 1

                          A Blue-Banded Blood Moon
                           Image Credit: Angel Yu

   Explanation: What causes a blue band to cross the Moon during a lunar
   eclipse? The blue band is real but usually quite hard to see. The
   featured HDR image of last week's lunar eclipse, however -- taken from
   Yancheng, China -- has been digitally processed to equalize the Moon's
   brightness and exaggerate the colors. The gray color of the bottom
   right is the Moon's natural color, directly illuminated by sunlight.
   The upper left part of the Moon is not directly lit by the Sun since it
   is being eclipsed -- it in the Earth's shadow. It is faintly lit,
   though, by sunlight that has passed deep through Earth's atmosphere.
   This part of the Moon is red -- and called a blood Moon -- for the same
   reason that Earth's sunsets are red: because air scatters away more
   blue light than red. The unusual blue band is different -- its color is
   created by sunlight that has passed high through Earth's atmosphere,
   where red light is better absorbed by ozone than blue. A total eclipse
   of the Sun will occur tomorrow but, unfortunately, totality be visible
   only near the Earth's South Pole.

                  Almost Hyperspace: Random APOD Generator
                Tomorrow's picture: small galaxy, local group
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