WHEN CAESAR DIED, a comet appeared in the sky and lurked for seven days. It was believed to be his soul.

"Fire and Ice: A History of Comets in Art," at the Air and Space Museum, says our perception of comets has evolved since then. We no longer see comets as portents of good or ill, but as "eloquent symbols of change and continuity within our universe . . . beacons of hope and inspiration for the discovery of new worlds."

Don't you believe it. Comets are spectacles, great theater, must-see shows in the sky- suite. And no one with a grain of superstition is going to rule out anything.

Looking at the exhibit's 90 artifacts and reproductions -- borrowed from such distant regions as the Vatican and the New York Public Library -- it's clear that comets in art always symbolize something. A comet's presence transforms a Mir,o landscape to one fraught with meaning, stirring something primitive in the viewer.

That reaction would have disappointed Edmond Halley, who showed comets to be predictable members of our solar system. In his introduction to Newton's "Principia," he wrote in 1686, "Now we know the sharply veering ways of comets, once a source of dread, no longer do we quail beneath the appearance of bearded stars."

Nonetheless, a woodcut 73 years later catalogues them as "Blazing Stars, Messengers of God's Wrath." And Jean Cocteau's 20th- century woodcut "Appolinaire au Front" shows the comet as a symbol of war. A comet meant battle long before Homer called it "the red star, that from its flaming hair shakes down diseases, pestilence and war."

But sometimes comets bode well. Halley's comet, as seen in 1301, heralds the birth of Christ in Giotto's "Adoration of the Magi" fresco painted in 1303. And Donati's comet, 1858, meant a fine vintage wine; here a beautiful woman represents that magnificent comet, which sported a thick-plumed duster of a tail, and two pencil-thin ion tails for good measure.

Comet fever burned, untouched by reason. Comets appeared not just in the sky but in glass pitchers and compotes, brass buttons, dropleaf table legs, hood ornaments and, of course, the Bayeux Tapestry.

The fascination being universal, we find that the 19th-century caricaturists whose works are on display here are talking about us. Daumier drew comet-hungry Parisians staring all agog out their windows, or submerging themselves fully clothed in the Seine, "taking care not to be roasted by the comet."

Roman philosopher Seneca thought that comets were pure fire. Now we know they're more like what astronomer Fred Whipple has called them -- dirty snowballs. And with Halley's comet a few months out, most of us have heard of the Oort cloud, the theoretical birthplace of comets (though few are likely to name a son after it). But there must be some primal reason why we persist in calling a comet's visit an "apparition."

Remember the Alamo, the great New York City fire and the Zulu massacre of the Boers? Halley's comet. They all happened in 1835, a Halley year. But it's important not to be paralyzed by fear. A 1547 history on display here tells how court astrologers advised Montezuma not to take action while a comet was in the sky. Thus fell the Aztec empire to Cort,es.