A coronal hole on the sun appears to be surrounded by solar activity in this image captured by NASA's Solar Dynamics Observatory in multiple wavelengths on Oct. 21, 2014.
A ring of solar activity appears to surround a coronal hole in this composite image taken on Oct. 21, 2014 by NASA’s Solar Dynamics Observatory in multiple wavelengths. Coronal holes are areas of the Sun’s surface that are the source of open magnetic field lines that head way out into space. They are also the source regions of the fast solar wind, which is characterized by a relatively steady speed of approximately 800 km/s (about 1.8 million mph). Credit: NASA/SDO