HALLEY: COMET 1986

Julius Caesar saw it, Samuel Clemens' birth and death coincided with its 1835 and 1910 passages, and its 1066 appearance was thought to foretell King Harold's defeat. (Branley assures us that views of the comet as an evil omen were ""completely unfounded."") Currently, ""there are many who support"" the ""dirty snowball"" theory. Every day thousands of tons of comet and meteorite dust fall on earth; and some of the particles show up as showers of shooting stars. In 1910 observers saw an electrically-charged plasma tail split from Halley's main dust tail. The 1950s established the theory of a vast dust cloud as ""the cradle of comets."" Branley falls out this quite unsystematic assemblage of diverting data with a rundown on notable comets: Donati's was spectacularly beautiful; comet 1861 II was spectacularly bright; Ikeya was discovered in 1963 by a 19-year-old Japanese amateur using a homemade $20 telescope; Kohoutek was a popular flop but provided scientific information. Halley's is not so much spectacular in itself as important for its namesake's prediction of its return--the first proof that comets moved in elliptical orbits around the sun. Halley's next visit will be most visible from Australia and New Zealand in April 1986; from the northern hemisphere it will peak in January 1986, but will probably be no brighter than a dim star. Branley hopes that Congress will approve a space probe to send back detailed photos; in any case, a joint European probe and probably others from the Soviet Union and Japan will be sent; a space-shuttle telescope and other instruments will be employed; and an eight-year International Halley Watch will be coordinated from Pasadena. Branley concludes with a warning not to get caught up in Halley hysteria. (One of the fears of 1910 was that the nitrogen in the atmosphere would turn to nitrous oxide and people would laugh themselves to death.) His comet alert appears to be hastily compiled and composed--more so than last year's entry by Anderson and Brown--but the light once-over, strengthened by a generous supply of photos and diagrams, is as sure a thing as Halley's return.