Satgen 196 Comet Swift - Tuttle by GM4IHJ 26 Dec 92 The BID of this msg is SGEN196 Please use it if you retransmit this msg For the moment the saga of Comet Swift - Tuttle has gone out of the headlines, so perhaps this is a good time to review what we have learnt. In 1862 S-T was seen as a very bright comet as it rounded the Sun on the 23rd of August. The similarity of its orbit, to that of the Perseids meteor shower was noted, and it was calculated that S-T would return in 1981. It did not do so. By 1981 Astronomers were much more aware of the connection between the passage of a comet, and , the increase in meteor activity when the Earth made its annual trip across the comets track, at a time when the comet was near the Earth. But the Perseids showers in 1980/1981 /1982 were poor. At which point with no S-T in sight the Astronomers looked again at the 1862 data and noted how vague it was. Then when they added the fact, (quite unknown in 1862 ) , that the comet could "rocket propel itself" by releasing gas when heated by the Sun, it became clear that S-T might come much later. Indeed one Astronomer did go on record predicting a Dec 1992 perihelion Sun passage, based on a previous possible sighting of Comet Kegler in 1737. So when in 1991 the Perseids shower was very good indeed, Astronomers started to look again for Comet S-T/Kegler, ( a case where most unusually Radio Amateurs were credited in professional astronomy reports). By August 92 however there had been no sightings of Comet S-T/Kegler. Then suddenly at 1900 ut on 11th Aug 92, we had one of the best ever Perseid meteor showers heard on UK radio bands. 7 weeks later on 26 Sept 92 a Japanese amateur astronomer sighted S-T coming towards the Sun. Then in late October and November, watchers had several good views of the comet in the UK evening sky. This was too good a story to end at that point. Examination of S-T's orbit suggested that next time around on 11 July 2126, the comet would miss hitting the earth by a mere 14 days. Which pessimists soon pointed out, could easily be accounted for by out gassing from the comet giving it a bit of rocket propulsion. Newspapers immediately published that collision was inevitable, and by an odd quirk of fate, their very dodgy reports coincided with a thoroughly factual professional geology paper confirming the existence of an immense 180 km diameter crater more than 1.3 kms deep, buried by subsequent erosion and deposition at the northern tip of Mexico's Yucatan peninsula. This crater has recently been dated at 65 million years old and it contains firm evidence of tremendous impact pressure. This date is important because it just happens to be when the Dinosaurs disappeared , along with most other life on the earth's land surfaces. Will S-T do a repeat performance in 2126, extinguishing the human race ( certainly as near a race of latter day Dinosaurs as it is possible to get ) ? Astronomers say " No, most unlikely". But before you quietly go back to sleep after your Christmas feast, please make a note in your diary that - After S-T's next visit in 2126, old friend Halley will come awfully close in 2134 , and if that misses, S-T in 2261 may come too close for comfort. So all things considered, these might be good dates to go and visit the in-laws on Mars. Happy New Year from Scotland, GM4IHJ @ GB7SAN