The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space.
The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space, sending coronal material speeding out in what is called a high-speed solar wind stream. The high-speed solar wind originating from this coronal hole, imaged here on Oct. 10, 2015, by NASA’s Solar Dynamics Observatory, created a geomagnetic storm near Earth that resulted in several nights of auroras. This image was taken in wavelengths of 193 Angstroms, which is invisible to our eyes and is typically colorized in bronze.
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Image credit: NASA/SDO