Solar corona. X-ray image of the Sun taken by the YOHKOH satellite of the eruption of a filament. The filament has a complex shape and is visible at upper and middle centre; it is formed in a region where a strong magnetic field bottles and accelerates coronal gases at high speed causing them to release a huge amount of energy in a relatively short period of time. This filament disappeared after only a few hours. The other bright areas are active regions in the corona where sunspots would be seen in visible light. The gas forming the corona has a very low density but high temperature (1 to 5 million degrees Kelvin) which causes the intense X-ray emission.