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Vulcan was proposed to explain a small perturbation in Mercury's orbit from the path predicted by classical mechanics, technically called advancing perihelion .
During Mercury's orbit, its perihelion advances by a small amount each orbit. The phenomenon is predicatable by classical mechanics, but the observed value differed from the predicted value by the small amount of 43 arcseconds per century.
This idea and the name "Vulcan" was postulated by the French mathematician Urbain Le Verrier in 1859, closely following his spectacular success in "discovering" the planet Neptune in the same way - using only calculus. Various persons and astronomers around the world attempted to prove the existence of the said planet.
In December 1859, Le Verrier received a letter from a French physician and amateur astronomer called Edmond Modeste Lescarbault , who claimed to have witnessed a transit of the hypothetical planet earlier in the year. Le Verrier took the next train to the village of Orgères-en-Beauce , some 70 kilometres southwest of Paris, where Lescarbault had built himself a small observatory. Le Verrier arrived unannounced and proceeded to interrogate the shy physician.
Lescarbault described in detail how, on 26 March 1859, he noticed a small black dot on the face of the Sun, which he was studying with his modest 3.75-inch refractor. Thinking it to be a sunspot, Lescarbault was not at first surprised, but after some time had passed he realized that it was moving. Having observed the transit of Mercury in 1845Events January 29 The Raven by Edgar Allan Poe is published for the first time New York Evening Mirror . March 1 President John Tyler signs a bill authorizing the United States to annex the Republic of Texas. March 3 Florida is admitted as the 27th U., he assumed that he what he was observing was another transit, but of a previously undiscovered body. He took some hasty measurements of its position and direction of motion, and using an old clock and a pendulum with which he took his patients’ pulse, he estimated the duration of the transit at 1 hour, 17 minutes and 9 seconds.
Le Verrier was satisfied that Lescarbault had indeed witnessed the transit of a previously unknown planet. On 2 January 1860Events March 6 Abraham Lincoln speaks against slavery in New Haven, Connecticut April 3 The Pony Express makes its first run. May 9 The Constitutional Union Party holds its convention and nominates John Bell for President of the United States. May 13 Batt he announced the discovery of Vulcan to a meeting of the Académie des SciencesThe French Academy of Sciences Academie des sciences is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. It was at the forefront of scientific de in Paris. Lescarbault, for his part, was awarded the Légion d'honneurThe Legion d'honneur (in English: Legion of Honor is an Order of Chivalry awarded by the President of France. First instituted by Emperor Napoleon I on May 19, 1802, it is one of the most prestigious French awards and the country's highest civilian honor. and invited to appear before numerous learned societies.
Not everyone accepted the veracity of Lescarbault’s "discovery," however. An eminent French astronomer, M. Liais, who was working for the Brazilian government in Rio de Janeiro in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault’s at the very moment that Lescarbault said he witnessed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated" (Popular Science, Volume 13, pages 732-735, 1878).
Based on Lescarbault’s "transit," Le Verrier computed Vulcan’s orbit: it revolved about the Sun in a nearly circular orbit at a distance of 21 million kilometres, or 0.14 astronomical units. The period of revolution was 19 days and 17 hours, and the orbit was inclined to the ecliptic by 12 degrees and 10 minutes. As seen from the Earth, Vulcan’s greatest elongation from the Sun was 8 degrees.
Numerous reports – most of them unreliable – began to reach Le Verrier from other amateurs who claimed to have witnessed unexplained transits. Some of these reports referred to observations made many years earlier, and many could not be properly dated. Nevertheless, Le Verrier continued to tinker with Vulcan’s orbital parameters as each new reported sighting reached him. He frequently announced dates of future Vulcan transits, and when these failed to materialize, he tinkered with the parameters some more.
Among the earlier alleged observers of Vulcan, the following are the most noteworthy (Astronomical Register, 1869):
Shortly after eight o’clock on the morning of 29 January 1860, F A R Russell and three other people witnessed an alleged transit of an intra-Mercurial planet from London (Nature, 5 October 1876). An American observer, Richard Covington, many years later claimed to have seen a well defined black spot progress across the Sun’s disk around 1860, when he was stationed in Washington Territory (Scientific American, 25 November 1876).
No successful observations of Vulcan were made in 1861. Then, on the morning of 22 March 1862, between eight and nine o’clock, another amateur astronomer, a Mr Lummis of Manchester, England, witnessed a transit. A colleague whom he alerted also witnessed the event. Based on these gentlemen’s reports, two French astronomers, MM. Valz and Radau, independently calculated the object’s orbital period, Valz deriving a figure of 17 days and 13 hours, and Radau a figure of 19 days and 22 hours.
On 8 May 1865 another French astronomer, Aristide Coumbrary observed an unexpected transit from Constantinople.
Between 1866 and 1878 no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of 29 June 1878, two experienced astronomers, Professor James Craig Watson, director of the Ann Arbor Observatory in Michigan, and Lewis Swift, an amateur from Rochester, New York, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun, and estimated its magnitude at 4.5. Swift, who was observing the eclipse from a location near Denver, Colorado, saw what he took to be an intra-Mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about 6 or 7 minutes from the "planet." Theta Cancri and the planet were very nearly in line with the centre of the Sun.
Watson and Swift were excellent observers. Watson had already discovered more than twenty asteroids, while Swift had several comets named after him. Both described the colour of their hypothetical intra-Mercurial planet as "red." Watson reported that it had a definite disk – unlike stars, which appear in telescopes as mere points of light – and that its phase indicated that it was approaching superior conjunction.
These are merely the more reliable observations of alleged intra-Mercurial planets. For half a century or more, many other observers tried to find the hypothetical Vulcan. Many false alarms were triggered by round sunspots, that closely resembled planets in transit. During solar eclipses, stars close to the Sun were mistaken for planets. At one point, to reconcile different observations, at least two intra-Merculrial planets were postulated.
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