Neptune
Neptune, the eighth planet away from the Sun, was discovered in 1846 by German astronomer Johann Galle, who based his finding on the mathematical predictions of French astronomer Urbain Le Verrier and English astronomer John Couch Adams. Because Neptune is so far way from the Sun—about 2.8 billion miles (4.5 billion kilometers)—it is difficult to observe. Very little was known about it until fairly recently. In August 1989, the U.S. space probe Voyager 2 flew by Neptune, finally providing some answers about this mysterious, beautiful globe.
Neptune is a large planet, with a mass 17 times that of Earth. The diameter at its equator is roughly 30,700 miles (49,400 kilometers). Neptune spins slightly faster than Earth—its day is equal to just over 19 Earth hours. It completes one...
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