Wednesday, August 11, 2010

The race goes to the swift

Meteor showers are associated with the orbits of comets. As comets travel along their trajectories, they shed part of their substance, icy dust blown away by the pressure of sunlight. As time passes, the tracks of comets become dirty spaces, littered with bits of dust moving in the same orbit as the comet. Every year in August the Earth intersects the orbit of Comet Swift-Tuttle, sweeping up debris. The tiny particles plunge into the Earth's atmosphere at 40 miles per second, where they are heated by friction and vaporize in streaks of light. Not "falling stars" or "shooting stars," but grains of icy rock making spectacular swan dives into the air.

Comets take their names from their discoverers. The parent comet of the Perseids was first observed in 1862 by Lewis Swift, a farmer and amateur astronomer of Marathon, New York. Tuttle nearly missed his moment for glory. When he observed the blur of light in the constellation Camelopardis, he thought it too bright to be a comet that had not been observed by someone else. He wrote it off as the already reported Comet Schmidt. Three nights later he realized his mistake and reported his observation, simultaneously with Horace Tuttle of the Harvard Observatory. Swift might have had the comet all to himself. By protocol, the two men share the honor of discovery.

When I wrote about this in Honey From Stone, in 1987, Comet Swift-Tuttle was five years overdue for its predicted return, which added a note of mystery and anticipation to my account. The comet was subsequently recovered in 1992, by the Japanese astronomer Tsuruhiko Kiuchi. The orbit has now been greatly refined. We'll next see the comet in 2126.

But wait! If we intersect the comet's path every August, what if the Earth and Swift-Tuttle arrive at the fatal spot at the same time? The comet is bigger than the object that wiped out the dinosaurs 65 million years ago. A collision would be of apocalyptic consequence.

Calculations suggest this is highly unlikely, at least for the next few thousand years (and obviously it hasn't happened for countless orbits in the past). But farmer Swift has his name attached to a potentially devastating object. He went on to discover a total of thirteen comets, although none as bright or as famous as the Perseid progenitor. For his discoveries he was awarded a gold medal by the Imperial Academy of Sciences in Vienna, and in the 1880s he was appointed to the directorship of the Warner Observatory in Rochester, New York. From the citizens of that city he received a 16-inch refractor telescope costing $11,000, with which he discovered more that a thousand nebulae, among them hundreds of distant galaxies.

In the Roman Catholic prayers of the Feast of Saint Lawrence, we hear again and again the martyr's purported words to the emperor Decius, who had promised the saint a night of pain: "Night has no darkness for me, all things become visible in the light." The words might aptly be applied to the ex-farmer of Marathon.