Is Earth's life in the solar system at the whim of comets?

This was one of the questions David Levy, nationally - known amateur astronomer, raised Tuesday in his speech, "Jupiter and Shoemaker 9: The Great Collision."

The speech was part of Auburn's Franklin Lectures in the Sciences and Humanities.

About 150 combined astronomy buffs, students and faculty at tended the speech in Broun Hall.

Levy received notoriety when he and fellow astronomer Gene Shoemaker discovered the now-famous comet which impacted with Jupiter in the summer of 1994.

"People have a natural curiosity with unknowns like space, which was placed within them from the earliest days," Michael Bozake, Auburn associate physics professor, said.

The comet's impact with Jupiter was featured on the covers of Time and U.S. News and World Reports.

"The comet was over four billion years old. We weren't here when it was born, but we saw it die," Levy said.

Levy, 47, began looking for comets in 1965.

His interest in outer space stems from his childhood and a book his father made him read Ñ Hamlet.

"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy,"

Shakespeare wrote.

This was the quote that helped inspire Levy to become, what he calls, "a nightwatchman of the sky."

For the first five years he didn't find anything. "It's not the di scovery, but the search that's the most important," Levy said.

But later Levy did begin discovering comets, culminating in his 1994 discovery at a California observatory.

Comets mean different things to different people, Levy said.

Singer and son g writer Mary Chapin Carpenter describes comets as, "a bit of heaven shot across the sky," in her song, "Haley came to Jackson," Levy said.

Levy describes comets as "huge balls of frozen snow."

He said that when a comet nears the sun, it heats and develops a luminescent cloud and an elongated vapor trail.

A typical comet is about 10 to 15 miles across, he said.

He said all the comets that have been seen prior to Shoemaker-Levy 9 have orbited the sun.

Shoemaker-Levy 9, however, was orbitin g Jupiter and, "it was making its final orbit," Levy said.

Pictures from NASA's Hubble telescope showed that the comet had been spilt into 21 pieces by the tremendous pulling force of Jupiter's gravity.

Jupiter's gravity acts more than 200 times str onger than the moon's gravity acts on the earth's water, Levy said. "Never before had nature given us such a glaring example of tidal force," he said.

Levy said the pictures of Jupiter's surface show thousands of surface impact areas where comets have hit over millions of years.

"Who would have thought we would be able to see one in our lifetime," he said.

He said the first of the 21 pieces hit Jupiter on July 16, 1994.

When Levy showed the audience actual footage of the comet hitting Jup iter there was a collective murmur from the crowd.

From a telescope's view the comet looked like a ball of light that began to grow on the surface of the planet when it hit, he said. Levy pointed to a small area of the light and said, "That's the s ize of the earth."

There was another murmur from the audience.

"If one Hiroshima-type bomb exploded every second for nine and a half years, it would equal the total energy when Shoemaker-Levy 9 hit Jupiter," Levy said.

U. S. Congress took note o f the collision, because it "was right in the Earth's neighborhood," Levy said.

In July of 1994 Congress voted to instruct NASA to begin a search for potentially Earth-threatening comets.

Levy said the last comet to hit the Earth did so 65 million y ears ago, causing the extinction of the dinosaurs.

A vast crater beneath Mexico's Yucatan Peninsula appears to be the site of the impact.

Levy said a comet the size of Shoemaker-Levy 9 hits the Earth once every 100 billion years.

"It's not someth ing to stay up worrying about, but it is interesting," Levy said.

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