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.

                                2019 July 22

                  HDR: Earth's Circular Shadow on the Moon
               Image Credit & Copyright: Cristian Fattinnanzi

   Explanation: What could create such a large circular shadow on the
   Moon? The Earth. Last week's full Moon -- the Buck Moon -- was so full
   that it fell almost exactly in a line with the Sun and the Earth. When
   that happens the Earth casts its shadow onto the Moon. The circularity
   of the Earth's shadow on the Moon was commented on by Aristotle and so
   has been noticed since at least the 4th century BC. What's new is
   humanity's ability to record this shadow with such high dynamic range
   (HDR). The featured HDR composite of last week's partial lunar eclipse
   combines 15 images and include an exposure as short as 1/400th of a
   second -- so as not to overexpose the brightest part -- and an exposure
   that lasted five seconds -- to bring up the dimmest part. This dimmest
   part -- inside Earth's umbra -- is not completely dark because some
   light is refracted through the Earth's atmosphere onto the Moon. A
   total lunar eclipse will occur next in 2021 May.

   Partial Lunar Eclipse in 2019 July: Some memorable images submitted to
                                    APOD
                 Tomorrow's picture: extragalactic ejection
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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.
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