Solar activity. False-colour image of the sun made in 'soft' X-ray wavelength (250-3000 electron Volts). Increasing brightness relates to increased X-ray intensity. Three highly-active regions may be seen, at top left, bottom centre and just right of centre. These regions are associated with sunspots, and are formed by local intensity increases of the Sun's magnetic fields. This concentrates the very hot (about 1 million Kelvin) inner corona of the Sun, which emits X-rays. The high energies found in such features may lead to the eruption of solar material in prominences and flares. The data for this image were gathered on 31 January 1978 by a sounding rocket.