A vast hole in the sun's atmosphere--a "coronal hole"--has opened up in the sun's northern hemisphere, and it is spewing a broad stream of solar wind into space. NASA's Solar Dynamics Observatory photographed the coronal hole during the early hours of Dec. 3rd:
Coronal holes are places where the sun's magnetic field opens up and allows solar wind to escape. Hot plasma flows outward at speeds exceeding a million mph. In the extreme-ultraviolet image, above, the boundaries of the coronal hole are traced by dashed lines; arrows indicate the escape of hot plasma.
Solar wind flowing from this coronal hole will reach Earth beginning ~Dec. 6th, and our solar wind environment will be dominated the stream for days after first contact. High-latitude sky watchers should be alert for auroras
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