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SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Asaph Hall (1829-1907), US astronomer and discoverer of the two satellites of Mars. He found these in 1877, when Mars was just 48 million kilometres from Earth. He found the smaller satellite first, followed by the larger, and named them Deimos and Phobos respectively, after the sons of Mars in Greek mythology. In 1876 he observed a large storm system on Saturn, known as the Great White Spot. By observing Saturn a number of times, he was able to calculate its rotational period of the planet, which he found to be 10 hours, 45 minutes. This has since been refined to 10 hours 14 minutes at Saturn's equator.
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