Although there is a bit of conjecture and legend surrounding shadow bands -- for years, scientists debated their underlying cause -- Joe Rao, an associate at the American Museum of Natural History’s Hayden Planetarium in New York, likens the effect of shadow bands to the appearance of twinkling stars.
“The atmosphere at times can be very unstable and very turbulent, and so we end up seeing that turbulence when we look up at the sky and the stars,” he tells Thrillist. “As those light beams go through the atmosphere, they’re kind of jiggled or move in such a manner that it would give the impression that they’re twinkling up in the sky.”
But they’re not actually twinkling, mind you. In truth, volatile pockets of air affect our perception of the stars back on the ground, giving them a shimmering, twinkling appearance when we look up at the sky.
This same phenomenon causes shadow bands to beam down to Earth from the sun, 93,000,000 miles away. As Rao explains, shadow bands are “a distortion of the final rays of sunlight, coming down through our atmosphere,” right before and after the moon completely covers the sun. During the “final moments of totality, you see these bands of light and dark, shifting, shimmering,” Rao says. So when you see a shadow band, you’re not witnessing magic, although it might appear that way. Instead, you’re seeing the edges of fleeting sunlight cutting through turbulence.
And yes, catching one of these things in the flesh is a bonafide rarity. For example, as Rao tells it: “I have been to a 11 total eclipses, and I’ve never seen a shadow band effect during a total eclipse.” But even so, there are things you can do to augment the likelihood of catching them. For starters, try bringing a white bed sheet or screen to the spot where you're viewing the eclipse and laying it down perpendicular to the sun. Most vibrantly white surfaces can often be host to shadow bands, even the doors of a white sedan.
The prevailing lesson though, is to pray for turbulent weather. “Your chances of seeing [shadow bands] will be accentuated by just how unstable the atmosphere is,” Rao explains. “If for example a storm has just passed by, or a cold front has just passed by, and it’s very breezy or windy, I think there’s a much better chance of seeing the bands, as opposed to seeing them when you have calm conditions.”
And with a glut of campsites still available for dirt cheap, all situated along the eclipse’s path, your chances might portend a rare brush with the shadow snakes that you'll never forget.