The Hunt for Vulcan ~ Thomas Levenson

A short but very interesting non-fiction book about the search for an unknown planet postulated to exist closer to the Sun than Mercury. Its existence was proposed in the mid 1800s to explain a very small discrepancy in the orbit of Mercury, specifically how that planet’s orbit precesses over time – that is, how a line drawn between its closest and furthest distance from the sun changes direction in space over centuries.

The discrepancy was first pointed out by the French astronomer Anton Le Verrier. Le Verrier was famous for his earlier prediction that an as-then unknown planet was slightly disturbing the orbit of Uranus. He calculated its position, and then was triumphantly vindicated by the discovery of the planet just where he had predicted it to be. It was later named Neptune.

The discrepancy in Mercury’s orbit was tiny indeed. But Newton’s laws of orbital motion were by then so well established, and the mathematics so clear, that the discrepancy needed explanation. Based on his triumphant discovery of Neptune, it is hardly surprising that Le Verrier proposed another as-yet unseen planet, this time closer to the Sun. The hunt was on! Every solar eclipse was an opportunity for observation, trying to see this world so close to the Sun’s bright disc.

Was the missing planet, dubbed Vulcan, ever discovered? Alas for Star Trek fans, Vulcan does not exist. The true explanation for the discrepancies in Mercury’s orbit was uncovered only with the aid of Einstein’s General Theory of Relativity in 1914 and its revelation of curved space-time.

I love this kind of scientific history. Thomas Levenson makes a fascinating story out of it, and does a great job of explaining the scientific issues involved.