Skyward May 2023

Skyward May 2023

Skyward May 2023

Skyward May 2023 David H. Levy March 23, 1993: Comet Shoemaker-Levy 9 Thirty Years On

The photograph is the discovery images of Comet Shoemaker-Levy 9. Photographs by David Levy using the Palomar 18-inch Schmidt camera, two eight-minute exposures. separated by about 1 hour and 45 minutes. A lot can happen in thirty years, especially when it involves comets and asteroids that creep across the sky, and even more particularly with comets that go bump in the night. Such is the case with Comet Shoemaker-Levy 9, which is by far the most important and seminal of the 23 comets I have discovered. The Jupiter-Comet story began for me on September 1, 1960, when I looked through a telescope for the first time. Jupiter was my target and I still recall that view. Years later, Gene Shoemaker proposed that Comet Shoemaker-Levy 9 might have been orbiting Jupiter as early as 1929, and that it made a close approach to Jupiter during the year I first sighted the planet. Obviously, I did not see the comet that night; neither did anybody else. On the first night of our March, 1993, observing session at the 18-inch Schmidt telescope at Palomar Observatory, Gene Shoemaker developed the first four exposures and found them all blank. It appeared that someone had opened the film box since our February session and exposed the films to light. Examining the pile of films, I suggested that the ones near the bottom might be partially usable. Gene developed one of them and agreed. We continued most of the rest of that night with the partially damaged films until about 3 am, when we switched to a new set of prepared films. On that same night, I guided an 8-minute exposure. It was difficult to stay centered on the guide star since the glow from nearby Jupiter was interfering. We then did three other fields of sky. Clouds arrived before we had a chance to begin the second set of exposures (so that each field would have two exposures). We stopped observing and left the building to examine the sky. I noticed a slight break in the clouds to the southwest. Gene teased me as being the ”eternal optimist.” We had a strange discussion about money. Gene said that it costs eight dollars each time we load a film into that telescope. When I suggested that $8 was not too much, Gene quipped, “That’s eight American dollars! Not that Canadian play money you try to get away with!” But after Carolyn agreed that there was a break coming, Gene said, “Let’s do it!” We somehow managed to take four exposures before more clouds came and ended the night. On the afternoon of March 25, the sky was completely cloudy with snow flurries. Gene was reading Time Magazine. I was working on a book about my favorite subject, comets. Carolyn was scanning the two Jupiter films. Suddenly she stopped, looked towards me, and exclaimed, “I think I have found a squashed comet.” As Gene got up to look, Carolyn approached me. “You are joking, of course?” I inquired. Carolyn shook her head. Gene then looked toward us with the most unusual expression I had ever seen on his face. Then I looked. There was a long bar of cometary smudge, with at least five darker centres, each with a tail going towards the top of the films. There was also a trail of cometary light stretching off either side of the central structure. We needed to get a confirming image. I telephoned my friend Jim Scotti, who was observing on the 36-inch diameter Spacewatch camera atop Kitt Peak in Arizona. He simply did not believe me when I explained what we had. He said he would try to find the time to take a confirming picture. Two hours later I telephoned him again. Jim simply grunted. “The sound you just heard,” he explained, “was me trying to lift my jaw off the floor. “Do we have a comet?” “Wow, do you guys ever have a comet.” That is the story of how we discovered Comet Shoemaker-Levy 9 in the pinnacle moment of our professional lives. Sixteen months later we watched, along with the rest of the world, as the pieces slammed into Jupiter at the incredible velocity of 60 kilometers (37 miles) per second. (a plane travelling that fast would cross the United States in just over a minute.) We spent some time with both then-vice president Al Gore and President Clinton. Impact week was unforgettable. And it all began with a single look at Jupiter through my first telescope, a cloudy night, and some damaged film, on the never-0to-be-forgotten night of the 23rd of March, 1993.

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