We’re safe. Comet Swift-Tuttle won’t collide with Earth on its next foray into the inner solar system in 2126. More good news: pieces of the comet will smash into our planet this month.
To many of us, comet fragments are old friends. I remember my summer campmates excitedly gathering at the lakeside for the annual Perseid meteor shower. Cheering each shooting star, we didn’t realize that the speeding sky-pebbles had fallen off a passing comet like feathers from a startled goose. Astronomers know that the August meteors are pieces of Swift-Tuttle, left in its wake and traveling in the same orbit. Until last year, however, no one knew just when the comet itself would show its face again.
It had last been seen in the mid-nineteenth century. With an uncertain orbital period, the comet could stay away indefinitely. The best calculations suggested it might reappear around 1981. It didn’t. But then, last September, a Japanese amateur using six-inch binoculars spotted the incoming tailless blob near the Big Dipper’s bowl; his eyes were the first to behold the comet since 1862.
Through the fall, telescopes around the world watched the comet creep through Hercules on its way to a slingshot loop around the sun in December. We all knew that this smudgy iceball--probably about the size of Brooklyn--was shedding particles that would reach our world ten months later. We could only wait.
This month the engagement comes due: our planet will plunge through Swift-Tuttle’s orbital path. Happily for Earth, the comet is somewhere else, but its icy fragments await us like a shower of confetti.
Suspicious clues that something odd was afoot have been reported for years. The Perseid meteors--named after the constellation Perseus, from which they seem to radiate by a trick of perspective--had an abnormally rich display in 1991. Their usual 60-per-hour frequency doubled during erratic outbursts. Then, last August, things really heated up, especially over the Far East. Observers described the finest Perseid performance of the century despite the unwelcome light of the full moon. Clearly, something was going on. Now we know: the comet itself, the father of the spectacle, was hurtling through the neighborhood.
Is it all leading up to a glorious 1993 climax, the finest Perseid pyrotechnics until the comet returns in the twenty-second century? Many astronomers think so. And this time the moon won’t rise until after midnight, a far better situation than last year. The only downside is that the fat crescent may interfere in the predawn hours, when the meteor show is usually most intense. But nobody knows for sure just when the peak will arrive, so the only safe course is to start observing at nightfall on August 11 and to stay with it.
Pick a spot away from lights, out in the country if possible, with a large expanse of sky. Spread a blanket and keep your eyes glued upward; the raisin-size invaders love to sneak across the sky at a sizzling 40 miles per second when you aren’t looking. Perseids are among the fastest meteors because they collide head-on with Earth.
Add science to the fun by carefully keeping count. Remember, over 60 per hour means you’re in the big leagues, witnessing more than merely the best meteors of your life. You can say you were there for the return of old Swift-Tuttle, the patriarch of summer fireworks.