Sunspot movement as seen by SOHO/SWAN
A sequence of 6 images of the Sun's activity over the period 5 to 21 April 2001.
Activity on the Sun is revealed by the glow of hydrogen gas in space that is excited by ultraviolet rays from the Sun and subsequently detected by SWAN on SOHO. The SWAN (Solar Wind ANisotropies) instrument observes this Lyman alpha emission from the whole sky, and in this way gives information on the level of activity on both the Sun's near and far side.
The Sun's rotation carries the activity from left to right in the images. The period covered in this sequence is roughly ½ a full rotation period of the Sun. Black areas are regions not observed by SWAN. The white glow on the far side of the Sun in the first image (2001/04/05) is due to the active region AR 9393, host to the largest sunspot group in 10 years.