Sunday, February 11, 2018
The transit of Venus across the face of the Sun in 2012, imaged in three colors of ultraviolet light.
The image was taken by the Solar Dynamics Observatory. The dark region toward the right is a coronal hole. Coronal holes are areas where the Sun's corona is colder and has lower-density plasma because there are lower energy and gas levels. Coronal holes are created when the Sun's magnetic fields arch away from already-thin areas in the corona. When these arches do not fall back immediately, solar particles escape at a rate great enough to create a lower density and lower temperature in that area (e.g., the coronal hole).
The next transit of Venus will occur in 2117.