Ghosts and Poltergeists – 26th October 2006

Tony Sizer gave us a seasonal talk on Ghosts and Poltergeists. The astronomical ghosts he mentioned mostly turned out to be optical effects mis-interpreted by the observers who “discovered” them. They included the non-existant large moons of Venus and Mars, which were eventually explained, quite literally, as gleams in the observer’s eye, multiple reflections off the observer’s cornea and the eyepiece he was using. A few of the ghosts did turn out to be genuine astronomical objects mis-interpreted by the observers concerned; perhaps the most remarkable being the planet Uranus being mistaken for a moon of Venus. Astronomical poltergeists have been rather more numerous. The best known is probably the planet Neptune, which was discovered because of the effects it had on the orbit of Uranus. Mathematical calculations led to a predicted location, and the new planet was discovered very near its predicted position. Subsequent attempts to extrapolate the process to discover a large planet orbiting beyond Neptune led to the discovery of Pluto, but the discovery owed a great deal more to the careful systematic work of its discoverer than to the mathematical predictions. Similar predictions also suggested that there should be a planet orbiting inside the orbit of Mercury. So certain were some that this planet existed that they even named it Vulcan. However, the mathematics used to predict Vulcan’s existance was eventually shown to be inadequate, and when it was corrected Vulcan vanished. Many other moons and asteroids have since been discoveerd by making predictions mathematically, and at least a few have been shown subsequently to have been pure chance. It was a fascinating evening’s talk, and by way of icing, members were able to use the Society’s new Meade Light Bridge telescope to view comet SWAN.

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