Ultraviolet glow in gas beyond the Sun (12 April 2001) as seen by SWAN on SOHO
Activity on the Sun's far side (left) is revealed by the glow of hydrogen gas in space, lit by ultraviolet rays from the Sun and detected by SWAN on SOHO. It is charted as if observed from a position beyond the Sun. This view joins with a corresponding impression of near-side activity (right) to cover the whole sky. The Sun's rotation carries the activity from left to right in both images. Black areas are regions not observed by SWAN. The white glow on the far side of the Sun is due to the active region AR 9393, host to the largest sunspot group in 10 years.