They have likewise discovered two lesser stars, or satellites, which revolve around Mars; whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost five; the former revolves in the space of 10 hours, and the latter in 21-1/2 hours; so that the squares of their periodical times are very near in the same proportion to the cubes of their distance from the centre of Mars; which evidently shews them to be governed by the same Law of Gravitation, that influences the other heavenly bodies.
Lemuel Gulliver writing upon the astronomers of Laputa, from Gulliver's
Travels, by Jonathan Swift, 1726
The planet Vulcan is presently known as the planet from which originated Mr. Spock, a character in the TV adventure series Star Trek. Vulcan is depicted as an intensely hot planet inhabited by a race that suppresses emotion and lives by logic. The creators of the television program who dreamed up this mythical planet were undoubtedly having a good laugh at the scientists whose search for a planet between Mercury and the Sun ended in a revolution led by Einstein.
Until the Mariner 10 spacecraft flew by Mercury in 1974, very little was known of the innermost planet of the solar system. Its orbit is so near to the Sun that it is seen only in the twilight of sunrise or sunset, and during an eclipse of the sun. Even with the most powerful telescopes, its features and nature could only be guessed at.
Into the 19th century, astronomers were not certain if gravitation was universal in nature or might be confined within our solar system. The French mathematician Urbain Jean Joseph LeVerrier had received the accolades of the scientific community for his prediction which prompted the finding of Neptune in 1846. According to Newton's theories, gravity is an invisible force which acts solely by attracting different masses towards each other. LeVerrier had supposedly predicted Neptune's orbit by the manner in which its mass disturbed the orbit of Uranus, thereby explaining the movements of the outer planets by universal gravitation. Then he set about to explain the movements of the inner planets of the solar system.
Mercury was the stumbling block. Despite the most careful calculations, Mercury's orbit seemed to race ahead in its movements about the Sun. According to Newton's theories, Mercury would be dragged forward in its orbit by the other planets, and the best observations showed he was correct. However, LeVerrier could not account for "43 seconds of arc" of the advance of its perihelion each century. If gravity was the same everywhere, what invisible force was tugging at Mercury?
At first, LeVerrier tried to determine if other material in the solar system was responsible. Comets, dust, meteors, and the zodiacal light did not seem to offer enough substance. If there were enough meteors and dust, they would be visible in the form of a ring about the Sun, like that of Saturn.
A country doctor at Orgeres, France, reported seeing an object the size of a planet cross the disc of the Sun on March 26, 1859. LeVerrier went to Orgeres and interrogated the amateur astronomer Lescarbault about the unidentified planetary object.
Mercury and Venus have been observed moving across the Sun's disc since 1631 and 1639 respectively. Sometimes the astronomers forgot when this happened. On November 5, 1789, La Concha at Montevideo reported an unknown planet crossing the Sun's disc. On May 5, 1832, Fisher at Lisbon reported another. And on May 8, 1845, Houzeau at Brussels reported yet another. I have confirmed in the contemporary almanacs, from 1788, 1829 and 1841, which these astronomers could have consulted, that on these dates Mercury had been predicted to move across the Sun's disc. Dozens of such reports exist, which do not coincide with the transits of Mercury and Venus; from these LeVerrier selected five observations in addition to Lescarbault's to calculate, in 1859, the orbit of a planet he named Vulcan.
Vulcan was a strange planet. LeVerrier determined details of its size and orbit from these six observations and the 43 seconds of arc of Mercury's advance in its orbit. LeVerrier made another prediction: Vulcan would cross the Sun's disc on March 22, 1877.
In 1846, LeVerrier pointed starward predicting a new planet would be discovered. Only two assistants at the Berlin Observatory looked. Neptune was found. On March 22, 1877, every astronomer seemed to be looking at the Sun for the passage of the new planet Vulcan. No one saw Vulcan.
But Vulcan did not disappear entirely. Like the alleged moon of Venus (reported up to 1791) or Houzeau's planet Neith (an amazing discovery by the astronomer who could not identify Mercury), Vulcan continued to exist in the scientific journals and textbooks, if not in the heavens. On July 29, 1878, a total eclipse of the Sun took place.
Prof. James C. Watson was interested in searching out Vulcan during this eclipse. If Vulcan would not reveal itself by crossing the Sun's disc, when LeVerrier predicted, it might be seen near the eclipsed Sun. Watson memorized the positions of all stars which would be around the Sun during the eclipse. If there was another bright object, he would be able to identify it as Vulcan. Watson advised Prof. Asaph Hall of the U.S. Naval Observatory in Washington that he had seen an unknown object while watching the eclipse at Separation, Wyoming:
I have the honor to report that at the time of totality, I observed a star of the four and four and a half magnitude in R.A. 8h. 26m. dec. 18 north, which is, I feel convinced, an intra-Mercurial planet.... There is no known star in the position observed....
Prof. Lewis Swift of the Dearborn Observatory watched this eclipse near Denver and said that he saw two unknown objects. As no one else watching the eclipse noticed any Vulcans, Swift's double observation and that of Watson's were critically questioned and soon discredited. According to the French astronomer Flammarion, the unknown objects were the stars Theta and Zeta in the constellation of Cancer; but this explanation is incomplete. The positions given by Watson and Swift did not agree with each other, meaning that at least three unknown objects as bright as planets had been reported by these professors.
With Vulcan having failed to cross the Sun when expected, and seen only during eclipses of the Sun by astronomers whose reputations were ridiculed, Mercury's advances remained a puzzle -- until Einstein.
According to Einstein's General Theory of Relativity, as announced in 1915, exactly 43 seconds of arc of Mercury's advance were accounted for by the differences between Einstein's gravitation using Riemann's geometry of curved space and Newton's gravitation using Euclid's geometry. Even the little-known advances of the perihelion of the orbit of Venus (about eight seconds of arc per century) and of the Earth (about five seconds of arc) can be explained by the General Theory of Relativity. Einstein was quickly embraced by astronomers and other scientists, most of whom did not understand his general theory.
Before alleged proofs of Einstein's theory were offered in the form of eclipse photographs and spectrographs showing a gravity shift of light, the only observation that supported the General Theory of Relativity was Mercury's peculiar orbit, which had been calculated by LeVerrier more than 55 years before. The early acceptance of Einstein's theory was not based on the results of any experiments but upon the appeal it had to astronomers, mathematicians and physicists, by apparently answering an old puzzle without any need for Vulcan.
In 1877, Prof. Asaph Hall discovered two small satellites orbiting Mars: Phobos and Deimos. Since Mercury, Venus and Mars had no known satellites before 1877, their masses could only be estimated by guesswork and their supposed gravitational influence upon other planets and comets. In 1877, the mass of Mars could be more accurately determined by observing these satellites -- and it shrank against the old estimates. Since 1878, Mercury's mass has varied in astronomy textbooks by more than 10 per cent of the current figure of 5.5 per cent of the Earth's mass; but in 1844, Mercury's mass was estimated to be more than three times as great as it is today.
It would seem the masses of these planets may change considerably without affecting LeVerrier's precise calculations about an orbit made over 130 years ago. Astronomers and physicists still repeatedly claim that Einstein's theory explains perfectly the "43 seconds of arc" of advance per century of Mercury's perihelion, which represents less than 10 per cent of its advance as explained by Newtonian physics. Some are more precise and say: "43.03."
An inhabitant of Vulcan might say that isn't logical.
"Heavenly ghost" was first published in The Whig-Standard Magazine (Kingston, Ontario), 24 (n. 24; March 30, 1991): 26.
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