Mercury is 3,000 miles in diameter, a much larger globe than the Moon. First record of its observation was in 265 B.C. Owing to its proximity to the Sun, it is difficult to see, never appearing in a dark sky; but every few years it may be found near the horizon, an hour after sunset, in April-May. Often it is crescent-shaped like the Moon. Mercury takes about 88 days to revolve around the Sun at a mean distance of 35,750,000 miles. Its velocity varies between 23 and 35 miles a second, being quicker when nearer the Sun.
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