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Path: utzoo!utcs!lsuc!msb
From: msb@lsuc.UUCP (Mark Brader)
Newsgroups: net.astro
Subject: How long has Halley's Comet been in present orbit?
Message-ID: <1017@lsuc.UUCP>
Date: Mon, 6-Jan-86 03:51:09 EST
Article-I.D.: lsuc.1017
Posted: Mon Jan  6 03:51:09 1986
Date-Received: Mon, 6-Jan-86 04:33:13 EST
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 25
Summary: How far has it been tracked back?


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