Spaceweather.com - 4/18/13
NORTHERN CORONAL HOLE: A dark coronal hole has opened up in the sun's northern hemisphere, and it is spewing a stream of solar wind into space. NASA's Solar Dynamics Observatory took this multiwavelength UV photo of the gap on April 18th
Coronal holes are places where the sun's magnetic field opens up and allows solar wind to escape. In the image, arrows denote roughly where the solar wind is going. Solar wind from this particular coronal hole should reach Earth's orbit on April 21-22. A direct hit is unlikely, though. Because of the coronal hole's high northern latitude, the solar wind stream is likely to brush only the northern half of Earth's magnetic field. Nevertheless, polar sky watchers should be alert for auroras when it arrives.
Link: Spaceweather.com
