A hole in the sun

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http://earthsky.org/todays-image/northern-lights-over-wisconsin-last-night

An extensive coronal hole in the sun’ corona rotated towards Earth over several days last week (May 28-31, 2013). The massive coronal area is one of the largest in a year or more. Coronal holes are the source of strong gusts of the solar wind that carry solar particles out to the Earth and beyond. They appear darker in extreme ultraviolet light images (here, a combination of three wavelengths of UV light) because there is just less matter at the temperatures we are observing in. Solar wind streams take 2-3 days to travel from the Sun to Earth, and the coronal holes in which they originate are more likely to affect Earth after they have rotated more than halfway around the visible hemisphere of the Sun, which is the case here. They have already generated some aurora here on Earth.

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