Shadow bands: Another rare eclipse phenomenon

Shadow bands: Another rare eclipse phenomenon

LOUISVILLE, KY (WAVE) - While many will look to the sky on August 21 during the total solar eclipse, another interesting phenomenon may be happening at their feet.

Shadow bands, also called shadow snakes, have been described as thin, wavy, parallel lines of alternating light and dark that undulate on plain-colored surfaces shortly before and after a total solar eclipse.

These bands can be seen by placing a large white sheet of paper on the ground. Although they have been documented on multiple occasions, NASA scientists said their visibility varies from eclipse to eclipse.

Scientists hypothesize that their movement, intensity and direction is related to the same phenomena that makes stars twinkle. According to NASA, shadow bands are caused by atmospheric turbulence. Light passes through turbulent cells of air in the atmosphere. These cells, or eddies, act as lenses, "focusing and de-focusing" the light just before eclipse totality.

Near totality, the Sun appears as a thin crescent only a few degrees wide, which is around the same size as the atmospheric eddies when seen from the ground. The bands are produced because the Sun's image is longer in one direction than another, NASA said.

Since theses eddies are different in each viewing location and with each eclipse, the appearance of shadow bands is seemingly random.

Although they may be difficult to photograph, shadow bands have been documented such as in the Youtube video below:

NASA has a few tips to catch a view of these elusive shadow bands:

  • A large one-meter square piece of white paper or poster board is essential. Use this as the screen and set up your camera to photograph or record continuous video of this screen as the crescent of the solar surface disappears at the start of the eclipse and reappears at the end of the eclipse.
  • Place your digital camera in “sports photography” mode so when you press the shutter, your camera will take a continuous stream of still images.
  • Make sure a meter stick is placed on the poster so that you can establish size.
  • Make sure that your pictures or video are time stamped so you can determine their speed and changes in intensity and direction.
  • Draw a line pointed in the direction of the eclipsing sun during totality and a line directed North-South and East-West.

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