Credit: NASA/SDO

The sun was visually dominated by three substantial coronal holes that rotated across its face the week of Sept. 8-10, 2015. Coronal holes are areas where the sun's magnetic field lines extend out into space and don't return to the sun.

This creates what's called an open , which is a source of solar particles streaming off the sun, known as the solar wind.

It is a little unusual – though not unheard of – to have three coronal holes at the same time. Coronal holes appear as dark areas in extreme ultraviolet light, because there is less material in the hole to give off light in these wavelengths. This image was taken in wavelengths of 211 angstroms, which is typically colorized in purple.

Provided by NASA