Solar activity. Comparison of false-colour X-ray (left) and visible light images of the Sun. This shows the correlation between sunspots (dark spots in visible image) and increased X-ray emissions (bright patches in X-ray image). Sunspots are associated with intense, localised magnetic fields. These fields also concentrate the ionised matter in the Sun's corona which is responsible for X-ray emission. Both images were taken on 25 October 1991. The data for the X-ray image were gathered by Japan's Yohkoh (Sun-ray") satellite in 'soft' X-ray energy (250-3000 electron Volts)."