NASA / SOLAR DYNAMICS OBSERVATORY / SCIENCE PHOTO LIBRARY NASA / SOLAR DYNAMICS OBSERVATORY / SCIENCE PHOTO LIBRARY
A pair of large coronal holes rotated into Earth's view on October 20, 2016. Coronal holes appear dark in certain wavelengths of extreme ultraviolet light, as seen here. These holes are areas of open magnetic field that spew solar wind into space. Sometimes, when they are facing Earth, they can cause geomagnetic disturbances that generate aurora. The lines here were drawn to represent how solar scientists are modelling magnetic field lines.
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