An Etymological Dictionary of Astronomy and Astrophysics
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A hypothetical small planet proposed in the 19-th century to exist in an orbit between Mercury and the Sun. In order to explain some characteristics of Mercury's orbit, the French astronomer Urbain Jean Joseph Le Verrier (1811-1877) hypothesized the presence of another planet, which he named Vulcan. Those particularities of Mercury's orbit were later explained by Albert Einstein's theory of general relativity.

L. Vulcanus in Roman mythology the blacksmith god of fire and volcanoes, a word of Etruscan origin