To man's naked eye the sun seems a smooth, bright disk. But astronomers have long known that its face is mottled with hot clouds of hydrogen gas, which seem to be the source of some of the radiation that periodically disrupts radio communication, and may have an important effect on the earth's weather. The clouds give off ultraviolet rays on the so-called Lyman-alpha line of the spectrum, midway between visible light and X rays. Since these rays are absorbed by the earth's atmosphere long before they can reach the ground, no earthbound camera has ever been able to make a...
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