Vulcan
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~15 min read
Encyclopedic overview
Vulcan in a lithographic map from 1846
Vulcan (/ˈvʌlkən/) was a proposed planet that some pre-20th century astronomers thought existed in an orbit between Mercury and the Sun. Speculation about, and even purported observations of, intermercurial bodies or planets date back to the beginning of the 17th century.
Excerpted from Wikipedia’s “Vulcan” article, available under the CC BY-SA 4.0 licence.