Lewis and Horace
Lewis Swift and Horace Tuttle came to discover a new comet in July of 1862. They published their discoveries within days of each other (July 16 and 19th respectively) and predicted that it would be visible from earth once again in about 125 years.Their prediction was close. The Swift-Tuttle comet was spotted again in 1992.
Changing Trajectory
The explanation for the prediction being off commonly given is that the comets trajectory changed slightly. It's not too difficult to volley up a hypothesis as to why a comet's trajectory could have changed - it could be the gravitational pull of any of the objects near it's path (such as the sun), or it may well have happened because of an explosion or some sort of extreme heat source in or near it's path.Brian Marsden took on the responsibility of predicting our next run-in with Swift-Tuttle. After it didn't show up on time, he did a little research and found another possible Swift-Tuttle sighting - in China in 1737. Using this sighting as a base, he predicted the comet would show up again in 1992. His calculation was off by 15 days.
He predicted our next visit by Swift-Tuttle as well - on August 14, 2126. The problem with this prediction however was the chance that he was again off by 15 days. If we see Swift-Tuttle on August 29, 2126 we're going to see it very well. We'll be directly in it's path!
My Bad
As the results of his prediction gained notoriety, and the impending doom becoming a bit more worrisome to the masses, Marsden changed his hypothesis. Whether it was done because of political pressure or because he actually saw the error in his calculations we'll find out in 119 years.The effect of a comet collision would be great, but it would be relatively local - this because a good deal of the comet would break up as it pierced our atmosphere. An asteroid anywhere near the size of the comet would be globally devastating however. NASA has proposed an early warning system so that we may predict collisions with roughly 90% accuracy and act on the knowledge with several decades of advance notice. Unfortunately, the cost of the project (about $.04 per American Taxpayer) is just too high - especially since no major collisions are supposed to happen within the next 75 years.
My Own Prediction
I'm going to venture my own prediction as to when we'll see Swift Tuttle. - August 21, 2126. On that day (10 + 21 + 2 + 1 + 2 + 6), the world will see a fireworks display so exciting that it can be described as the Answer to Life, The Universe, and Everything.42 is what you get when you divide the mass of the universe by 3 sightings x 10^42kg. Courtesy of Deep Thought's calculation of 6 times 9 in base 13.
Yeah, I know I sound loopy, but at least 1 of the 900 people checking out this page today will get the joke.
Swift-Tuttle - is it coming? Interaction
