msb@lsuc.UUCP (Mark Brader) (01/06/86)
As we all know, Halley's Comet is known to have been observed in every appearance since 240 BC. And according to Isaac Asimov's essay "The Long Ellipse" (in the collection "'X' Stands for Unknown), we also have records of the 467 BC appearance, though not the two intervening ones. My question is whether anyone has tried to work out how many orbits the comet had made before that. After all, a comet coming in from the Oort cloud (or wherever) doesn't just go into a 76-year orbit spontaneously; there must have been an encounter with one of the planets from Venus to Neptune, most likely Jupiter, of course. The orbits of the planets are well known and we must have, from all the historical records and from calculating backwards, some fairly good idea of what the orbit of Halley's was like then (despite all the perturbations since -- or do they cancel out anyway?). So has anyone calculated back to find the decisive encounter that is responsible for the 76-year orbit? Mark Brader "As the comet neared its closest approach to Earth [in 1910], The New York Times reported that not one telescope, regardless of its optical quality, remained for sale in North America." -- Terence Dickinson, Toronto Star, January 4, 1986
GMS@PSUVM.BITNET (01/10/86)
This really dosen't answer the question of how long P/Halley has been in
its present 76-year orbit. I just wanted to point out that there
are nongravitational forces which act upon the orbits of comets. The
one I read about most often is ourgassing from the comet itself. These
forces may accumulate over time and thus make the tracing of orbits
into the past less accurate.
However, the question does raise another point. If there are bodies beyond
the orbit of Pluto, might it be possible, through a study of many
trans-Pluto comets to infer where any such massive bodies (planets,
brown dwarfs, etc.) might be found?
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wiener@idacrd.UUCP (Matthew P Wiener) (01/12/86)
> However, the question does raise another point. If there are bodies beyond > the orbit of Pluto, might it be possible, through a study of many > trans-Pluto comets to infer where any such massive bodies (planets, > brown dwarfs, etc.) might be found? Actually, some astronomers have made predictions since c.1910 about trans-Neptunian/Plutonian objects based on comet studies. Indeed, one other astronomer (whose name escapes me) deserves equal credit with P Lowell for the prediction of Pluto. (Perhaps because he also predicted several other planets, and could not afford his own ob- servatory, and at first dismissed Pluto as just a comet, he has been lost in obscurity.) But yes, such studies can and have been done in more recent years, but they all need too many assumptions about the object to make a prediction about where it is now. berkeley!brahms!weemba Matthew P Wiener Math Dept UCB Berkeley CA 94720