The Hunt for Vulcan, by Thomas Levenson

While the story of Vulcan is relatively short, the majority of this book is spent covering the science that led up to how this colossal mistake called Vulcan was made. It started with the triumph of mathematics and observational accuracy that led to the discovery of Neptune in 1846. It was almost exactly where the mathematician Urbain La Verrier predicted it would be, using the unexplained deviations in the orbit of the planet Uranus. La Verrier reasoned that another planet must be influencing Uranus’ orbit, and he was right. The planet was discovered within on hour of the initial search with a telescope.

Largely due to this success, La Verrier used the same approach to explain the error in Mercury’s orbit. Mercury’s orbit was also a mystery–its orbit did not fit any calculations. So, La Verrier assumed that another planet was causing the problem. His argument was so convincing, and his reputation so impeccable, that astronomers were soon announcing that they had seen this planet–presumptuously named Vulcan. After one well known astronomer announced that he saw it, the New York Times published “there is an end of all discussion. Vulcan exists…” But Vulcan refused to appear. Le Verrier even made a prediction that Vulcan would transit the Sun in early October of 1876. But, it did not appear.

In the end, Albert Einstein is the scientist that destroyed Vulcan, and he did it with his pen. He was able to show why there was an error in the calculations of Mercury’s orbit with his Theory of General Relativity. Mercury’s orbit was influenced by the alteration of space caused by the Sun’s mass. It was confirmed during the eclipse of  1919, when astronomers could show that the Sun actually shifted light from other stars as it passed the sun.

My Notes:

Arthur Halley came up with the inverse square law of gravity, and was trying to relate it to the orbits of the planets.  Isaac Newton provided him with the mathematical answer, as orbits being in the shape of an ellipse. Halley confirmed the law by predicting the return of comet Kirch in 1680.

Herschel discovered Uranus, and LaPlace refined the mathematics of the solar system to the point he could show how Jupiter and Saturn affected each other’s orbits. Le Verrier continued with LaPlace’s work, but his work revealed two anomalies; Mercury’s orbit deviated slightly from calculations, and Uranus appeared to be influenced by another body. This led to Le Verrier computing the orbit of a mystery planet that would explain Uranus’ behavior. That led to the discovery of Neptune.

Le Verrier used the same reasoning to conclude that perhaps another planet inside the orbit of Mercury could lead to explaining its odd behavior–thus, the creation of a ghost planet called Vulcan.

So convinced were astronomers that some actually reported sighting this planet. Several publications, including the New York Times, which published “there is an end of all discussion. Vulcan exists…” But Vulcan refused to appear. Based on one supposed sighting by a well known astronomer, Le Verrier even made a prediction that Vulcan would transit the Sun in early October of 1876. But, it did not appear.

One last attempt was made in the total eclipse of 1878. The absence of the Sun’s light would give astronomers a chance to see the planet against a dark sky. And one observer had success. Leading to this publication in the Laramie Weekly Sentinel, “professor Watson of Ann Arbor, Michigan…had take the job of finding Vulcan. He found it.” A confirmation was also published, again, in the New York Times. But, alas, that observation also, could not be confirmed by anyone else, and that concluded the existence of Vulcan.

Other attempts were made to explain the Mercury problem. On astronomer even suggesting the need to tweak Newton’s law of gravitation by a tiny amount.

Ultimately, in November of 1915, Einstein’s pen destroyed Vulcan. His general theory of relativity led to the exact amount needed to explain Mercury’s orbit–a perihelion advance 43 arc seconds per century.

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