Giant hole in sun's atmosphere seen by orbiting observatory

GREENBELT, Md., July 22 (UPI) -- NASA says a U.S.-European solar observatory has observed a giant example of a phenomenon knows as a coronal hole in the sun's outer atmosphere.

The European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO, captured an image of a huge coronal hole hovering over the sun's north pole on July 18, NASA reported Monday.

Dark, low density regions of the sun's corona, its outermost atmosphere, coronal holes contain little solar material and have lower temperatures, making them appear much darker than their surroundings.

Such holes are a source of a high-speed wind of solar particles that streams off the sun some three times faster than the slower wind elsewhere in the sun's atmosphere, creating space weather that can affect satellites in orbit and communications on Earth, NASA said.

The exact cause of coronal holes is unclear, scientists said, although they appear to correlate to areas on the sun where magnetic fields rise up and away, failing to loop back down to the sun's surface as they do elsewhere.