Solar corona. X-ray image of the activity of the solar corona obtained by the Normal Incidence X- ray Telescope (NIXT). The image was taken before the onset of a solar eclipse and the round feature at right shows the shadow of the lunar disc. The corona is formed by gas at very low density but an extremely high temperature (1 to 5 million degrees Kelvin) which causes the intense emission in the X-ray band. The brightest areas are solar active regions where sunspots would be seen in visible light; the darkest regions are coronal holes where the gas density is extremely low and from which the solar wind, a stream of charged particles, is ejected into the interplanetary space.