ISAAC ASIMOV called them "the closest thing there is to nothing at all." Astronomer Fred Whipple dubbed them "dirty snowballs." In medieval days, they foreshadowed plagues and observers died of fear just looking at them. But despite all the bad press, they are the stars of the latest show, "Comet Quest," in the Air and Space Museum's planetarium.

The most popular, though probably not the dirtiest, iceball of all is the one discovered by Edmund Halley (rhymes with tally). We can expect to see this comet with binoculars in November 1985, and possibly with the naked eye in March or April of '86. That gives you enough time to make your own telescope -- and certainly to take in this show.

Planetarium shows are becoming flashier. "They're competing with Star Wars -- the movie, that is," says David DeVorkin, one of the masterminds behind this one.

Although the planetarium instrument (Carl Zeiss Model VI with accessories) projects the stars, its head is tucked away discreetly, not looming alarmingly like a space monster in the middle of the domed room, as in many such shows.

We have an unobstructed view of the sky -- The Milky Way as we don't see it. Orion, the Pleiades, Pegasus and Cassiopeia crawl overhead, as actress Mariette Hartley narrates.

At the mention of Aristotle, fires burn in ancient Greek temples along the horizon. Then the Bayeux Tapestry unfurls, to reveal a comet moving toward King Harold of England. (Halley's did show up in 1066, when William the Conqueror was invading.)

The special effects don't stop. In smooth segues, the planetarium show spins out clouds of dust and gas, flying space probes, shimmering zodiacal light, crashing comets, floating gas masks.

Gas masks? Although sometimes material is ejected at the rate of an exploding star, it's manageable. Gas masks -- not to mention comet insurance -- were purchased by the prudent for the last visit of Halley's comet, in 1910, after Yerkes Observatory announced that the tail contained cyanogen, a poisonous gas.

It may be a lot of fuss about a feathery fleck up in the sky -- but "Comet Quest" is well worth the crick in the neck.

COMET QUEST -- At the Albert Einstein Planetarium in the Air and Space Museum.