Until now, you had to be pretty much of an astronomy nut to see Comet Hale-Bopp. Not that the comet is especially hard to spot. For weeks it has been putting on a show to rival last year's Comet Hyakutake. People have seen Hale-Bopp, without a telescope or even binoculars, from such unpromising, light-polluted vantage points as midtown Manhattan and downtown Chicago. Amateur astronomers have been taking telescopic photos of the comet for well over a year; the Jet Propulsion Laboratory's Hale-Bopp home page on the World Wide Web NewProducts.jpl.nasa.gov/comet has posted more than a thousand already, and more are streaming in all the time. The problem, though, is that Hale-Bopp is still what is called an early-morning object, up before the sun and invisible before most folks are out of bed. A spectacular comet is one thing; getting up at 5 a.m. is another.
But that's about to change dramatically. By the end of next week, Hale-Bopp's path across the sky will take the comet right into prime time. By April 1 or so, when it makes its closest approach to Earth, the comet will be high in the evening skies over the northern hemisphere, brighter than ever and showing a short but prominent tail. And there it will sit, not for a measly week like Hyakutake, but for more than a month. "I predict that this could be the most viewed comet in all of human history," says Daniel Green, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "This will be one of the brightest objects in the sky. It'll be hard for the average person not to see it."
All this may come as news to most of us, but astronomers, amateur and professional alike, have been buzzing about Hale-Bopp ever since its discovery nearly two years ago. At that point the comet was more than half a billion miles from the sun, well beyond the orbit of Jupiter, and invisible without a telescope. But not necessarily a huge telescope: like most comets, this one was found by a pair of amateurs as familiar with their favorite regions of the sky as most people are with their own neighborhoods.
On July 23, 1995, Alan Hale, who has a Ph.D. in astronomy and makes his living running a research and educational company, was scanning the skies above his home in Cloudcroft, New Mexico. He was waiting for an already discovered comet to rise over his house when he trained his telescope on M70, a well-known cluster of stars in the constellation Sagittarius. "As soon as I looked," he says, "I saw a fuzzy object nearby. It was strange, because I'd looked at M70 a couple of weeks earlier and the object hadn't been there."
Hale checked his sky atlas, then logged on to the computer at the quaintly named Central Bureau for Astronomical Telegrams, located at the Harvard-Smithsonian Observatory. Maybe this would turn out to be a known object. It didn't. "Now I felt I had a pretty live suspect," he says. He fired off an E-mail message to Daniel Green and Brian Marsden, who run the Bureau for the International Astronomical Union, reporting a possible new comet. A few hours later he looked again, and the object had moved. It was a comet for sure.