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Concept
Vulcan (hypothetical planet)
Summary
Vulcan 'vVlk@n was a theorized 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. The case for their probable existence was bolstered by the French mathematician Urbain Le Verrier who, by 1859, had confirmed unexplained peculiarities in Mercury's orbit and predicted they had to be the result of gravitational influences of another unknown nearby planet or series of asteroids. A French amateur astronomer's report that he had observed an object passing in front of the Sun that same year led Le Verrier to announce that the long sought after planet, which he gave the name Vulcan, had been discovered at last.
Many searches were conducted for Vulcan over the following decades, but despite several claimed observations, its existence could not be confirmed. The need for the planet as an explanation for Mercury's orbital peculiarities was later rendered unnecessary when Einstein's 1915 theory of general relativity showed that Mercury's departure from an orbit predicted by Newtonian physics was explained by effects arising from the curvature of spacetime caused by the Sun's mass.
Celestial bodies interior to the orbit of Mercury had been hypothesized, searched for, and even claimed as having been observed, for centuries.
Claims of actually seeing objects passing in front of the Sun included those made by the German astronomer Christoph Scheiner in 1611 (turned out to be the discovery of sunspots), British lawyer, writer and amateur astronomer Capel Lofft's observations of 'an opaque body traversing the sun's disc' on 6 January 1818, and Bavarian physician and astronomer Franz von Gruithuisen's 26 June 1819 report of seeing "two small spots...on the Sun, round, black and unequal in size". German astronomer J. W. Pastorff reported many observations also claiming to have seen two spots, with the first observation on 23 October 1822 and subsequent observations in 1823, 1834, 1836, and 1837; in 1834 the larger spot was recorded as 3 arcseconds across, and the smaller 1.
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