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This image highlights the outer atmosphere of the sun, called the corona, as well as hot flare plasma. Hot active regions, solar flares and coronal mass ejections appear bright here. The dark areas, called coronal holes, are places where very little radiation is emitted. But these holes are the main source of solar wind particles. (NASA)

Coronal Holes: The (Rarely Round) Gaps In The Sun's Atmosphere

Sep 5, 2013 (All Things Considered)

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There's a hole in the sun's corona. But don't worry — that happens from time to time.

"A coronal hole is just a big, dark blotch that we see on the sun in our images," says Dean Pesnell, project scientist for NASA's Solar Dynamics Observatory. "We can only see them from space, because when we look at them [through] a regular telescope, they don't appear."

That's because you have to look at wavelengths of light that the human eye can't see. As the name suggests, coronal holes are holes in the sun's corona, not the sun itself. The corona is a hot and glowing outer layer of atmosphere that surrounds the sun. It extends millions of miles into space.

Pesnell says scientists aren't really sure where coronal holes come from. "Some people claim that they are the skeleton of old sunspots," he says.

Sunspots are also dark blotches, but they're on the surface of the sun, below the corona. They're caused by strong magnetic fields that cause cool regions — which look dark — to form on the sun's surface. The idea is that when sunspots fade away, they leave behind a coronal hole.

One thing scientists do know for sure about coronal holes is that they're not round. "They have all kinds of cool shapes," Pesnell says. "We've seen [some] that look like rubber chickens. My favorite is the one that looks like Kokopelli, a flute player from Native American cultures in the Southwestern U.S."

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