DUNKLIN COUNTY, Mo. — As mid-day darkness covered the landscape Monday and the visible part of the sun was reduced to a sliver — immediately before and after eclipse totality swept across parts of the region — some viewers noticed a dazzling spectacle on the ground, in addition to the one overhead.
In the dim conditions, waves of faint light rapidly cascaded across the ground’s surface — similar to the way refracted light shimmers across sand in shallow water.
One science professor at Washington University in St. Louis had waited years for another chance to see the “undulating” waves of lights, known as “shadow bands” — even draping a white sheet across the ground at his viewing location in Bollinger County, trying to enhance their visibility.
“They’re really cool. ... They look like these dark and light waves,” said Mike Krawczynski, an associate professor of earth, environmental and planetary sciences at Washington University, who saw them during the 2017 eclipse that also immersed the region — and parts of St. Louis — in totality. “It took me by surprise in 2017.”
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Krawczynski said comparing shadow bands to how light appears in water is appropriate — especially because the same principles are at play, as light gets refracted in the atmosphere.
It’s also the same reason that stars can appear to “twinkle” in the night sky. The light from them is so miniscule and faint that it can appear distorted or interrupted, as it passes through the atmosphere’s air and moisture before reaching the eyes of earthbound viewers.
The sun is ordinarily far too bright for people to observe the same phenomenon — except for when total eclipses occur, and the sun’s light is fleetingly made faint enough, producing shadow bands.
“It starts to act more like a star and we notice the twinkling,” Krawczynski said.
‘The main fun of an eclipse’
All eclipse experiences aren’t created equal from event to event, even for those who make it to the middle of the path of totality, under clear skies.
For instance, eclipses can last different lengths of time. They last longer when the moon is closer in its elliptical orbit to the Earth.
That difference adds up, as seen in places like Carbondale, Illinois, which — thanks to tremendous cosmic fortune — practically received two direct hits in the path of totality in 2017 and Monday.
In 2017, the city’s eclipse totality lasted for about 2 minutes and 40 seconds, compared to 4 minutes and 8 seconds on Monday.
But there were other differences between the events — ones that may have made Monday’s eclipse even more spectacular than its predecessor.
Krawczynski said the sun’s activity can vary on a roughly 11-year cycle, and that this year is closer to a peak, while 2017 was near a minimum.
He said that difference means that even features of the total eclipse’s halo-like corona can vary, event to event. Besides looking for shadow bands on Monday, he was keen to watch for more dramatic bursts of light at its edges, called “prominences,” which appeared as bright pink spots.
Prominences are eruptions that occur around the surface of the sun, and — though not nearly as big as a solar flare — are still massive. Krawczynski said the biggest one visible on Monday was bigger than the Earth.
“I was really looking forward to some bright prominences ... and we got that,” he said. “There was one very prominent prominence, if you will.”
He also thinks that this year’s corona appeared brighter, and said Tuesday that he was hoping to confirm that by comparing photos from the two eclipses.
“I suspect you’ll see that the corona looked stronger yesterday,” said Krawczynski. “With the sun’s cycle, that’s what you would expect.”
The region’s two recent brushes with totality have provided exciting opportunities to expose the general public to the wonders of science and the universe, Krawczynski said.
“That’s the main fun of an eclipse,” he said. “That’s one of the things that drives me. Sometimes people go to these things and they become eclipse chasers after that.”