Shadow snakes or shadow bands are wavy lines of light and dark that race across the ground just before and after the moon totally blocks out the sun during a total eclipse.
Scientists still don't completely understand what these mysterious bands of light and shadow are or where they originate, according to NASA.
Over the past 100 years many scientists have tried to explain shadow bands, and since 1925 many believe the popular theory that they originate in the atmosphere.
"The intensity, motion and direction of these bands seems to be related to the same phenomenon that makes stars twinkle," NASA said on its website.
“In the upper atmosphere there are turbulent cells of air that act like lenses to focus and de-focus the sharp-edged light from the solar surface just before totality.”
Those turbulent air cells could cause the undulating shadows on the ground just before the moon blocks out the sun in a total solar eclipse.
Unlike the eclipse itself, shadow snakes are totally unpredictable and difficult to photograph, but you can see the bands during a total solar eclipse by looking at a plain-colored surface right before and after the moon moves in front of the sun.
#Eclipse2017 LIVE: Through the Eyes of NASAOn Monday, Aug. 21, all of North America will be treated to an eclipse of the Sun, and NASA will carry it live from coast to coast from unique vantage points on the ground and from aircraft and spacecraft, including the International Space Station. Coverage starts at noon ET/9am PT on Aug 21. Watch it live here on NASA's Facebook page or on your TV with the Facebook video app, available in major TV app stores. #Eclipse2017
Posted by NASA - National Aeronautics and Space Administration on Monday, August 21, 2017
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