CORONAL HOLE: A large "coronal hole" has formed in the atmosphere above the sun's northern hemisphere, and it is spewing solar wind into space. NASA's Solar Dynamics Observatory took this picture of the UV-dark gap during the early hours of June 19th:
Coronal holes are places where the sun's magnetic field opens up and allows the solar wind to escape. A wide stream of plasma flowing from this particular coronal hole will reach Earth, and brush against our planet's magnetic field, on June 23-24. High-latitude sky watchers should be alert for auroras on those dates. Aurora alerts: text, voice.