English: NASA successfully launched more than 200 Earth-orbiting satellites, including Goddard's eighth Orbiting Solar Observatory aboard this Delta rocket on June 21,1975, at Cape Canaveral, Florida. The satellite-the final in a series of spacecraft specifically designed to look at the Sun in high-energy wavelength bands that scientists cannot see on Earth-gathered data on energy transfer in the Sun's hot, gaseous atmosphere and its 11-year sunspot cycle. Sunspots are cooler regions that appear as dark patches in the visible surface of the Sun and are more plentiful every 11 years. Flares and other powerful solar events that sometimes wreak havoc with Earth's communications systems also are associated with heightened sunspot activity. In addition to looking at the Sun, the satellite investigated celestial sources of X-rays in the Milky Way and beyond. It carried eight experiments.