Skylab, America's first space station launched on 14th May 1973, carried the Apollo Telescope Mount which contained eight instruments to study the sun at various wavelengths. The corona, the outer area of the Sun's atmosphere, is very hot, with temperatures of a million degrees Kelvin, and is a powerful emitter of X-rays. X-ray astronomy is useful for observing variations in the structure of the corona, which changes according to the solar activity cycle. The brighter areas are emitting more X-rays than the surrounding darker regions. They are solar flares, or prominences, sudden outbursts of energy from the Sun's surface which reach into the corona. Flares occur near sunspots on boundaries dividing areas with opposite magnetic fields.
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