ight," says the Arizona-based writer and amateur astronomer David Levy, an ex-Montrealer who co-discovered a comet that slammed into Jupiter in July, 1994. "It's very active under the telescope. It's spouting jets of dust and gas just like a volcano."
This comet, like all others that orbit the sun, was shaken loose at some point in the cosmic past from a ring of debris - scraps left over from the Big Bang - that surrounds the Solar System. Since then, it has been following a long, wide path that takes it out beyond Pluto and then back towards the sun. The comet last passed by the Earth 4,200 years ago, says Marsden, about the time that ancient Chinese emperors began hiring court astronomers to record unusual celestial events such as eclipses and the appearance of comets - although there is nothing in their records to suggest that they saw Hale-Bopp. They had no scientific explanation for the celestial visitors, interpreting them instead as signs of impending misfortune.
On this pass, Hale-Bopp will reach its closest point to Earth - 190 million km - on March 23. By comparison, Hyakutake, a comet that was visible to the naked eye for about a week in late January, 1996, came within nine million kilometres. But because of its enormous size and volatile makeup, Hale-Bopp could put on a much more impressive show. Observers say the comet already has a spectacular tail - a shimmering stream of dust and ice particles possibly as much as 50 million km long. Heat from the sun appears to be continually unleashing material from its core. "As the nucleus rotates and certain active areas are exposed to sunlight, they start erupting," says Levy. "They produce magnificent jets. It doesn't take much to get them going, just a little bit of sunlight."
But for all the anticipation surrounding Hale-Bopp, many astronomers, professional and amateur, are keeping their enthusiasm guarded. Other comets, after all, have arrived in Earth's neck of the Solar System laden with great expectations, only to fizzle. As close as it was in celestial terms, Hyakutake, for example, appeared as little more than a smudge against the night sky because its tail was largely invisible gas. Before that there was Kohoutek, touted as one of the comets of the century when it was discovered in March, 1973. But its brilliance, caused by the vaporization of unusual gases in its nucleus, had faded by the time it was visible from Earth in December of that year. For all its promise, Hale-Bopp has behaved erratically since its discovery, alternately flaring up and fading, making it impossible to predict just how it will behave over the coming month.
According to Marsden, about a dozen comets are discovered every year, most of them too far away or too faint to be of interest to the public. Amateurs are responsible for a third to half of those discoveries. Some, like Levy, who has found nine since the early 1970s, spend dozens of nights each year systematically scouring the night sky for comets. But for others, like Bopp, finding a comet is pure serendipity. He and a friend were taking turns on a telescope, examining star clusters within the constellation Sagittarius from a site about 150 km south of Phoenix, when the comet drifted into his field of vision. "I had never looked in that area of the sky before," he recalled. "I was stepping from cluster to cluster, observing them for their beauty, when a little fuzzy glow appeared. I thought I had a faint galaxy or something."
But when they saw the object moving against the background stars, they quickly concluded it was a comet. Bopp drove home in a hurry and sent a telegram to Marsden's agency, reporting the find. "At 8:25 the next morning, my wife woke me and said somebody was on the phone from the Harvard-Smithsonian something or other," he recalled. "It was the Center for Astrophysics calling to confirm the report. When I hung up I did a comet dance around the kitchen table." Now, like stargazers everywhere, Bopp can only wait and watch and hope that his comet lives up to its advance billing.
Maclean's March 10, 1997