The Sun in extreme ultraviolet light, photographed by Skylab, 1973.

Skylab, America's first space station launched on 14th May 1973, carried many scientific experiments. The biggest was the Apollo Telescope Mount which contained eight instruments to study the sun at various wavelengths, including the extreme ultaviolet. Because the Earth's atmosphere intercepts much of the ultraviolet radiation, it was not posible to observe the Sun at these wavelengths until telescopes could be deployed in space. The Sun's emisions of extreme ultraviolet radiation increase during the solar maximum, the period of increased sunspot and solar flare activity which occurs roughly every 11 years.