The comet that hundreds of millions of people may see during the next two months was discovered on the night of July 22, 1995, by a concrete company worker at an informal "star party" in the Arizona desert and independently by the head of a private research center who was standing in his driveway in New Mexico. Thomas Bopp, an amateur astronomer who works in the parts department of a concrete supply company, had led friends about 90 miles south of Phoenix to a prime star-gazing site in the desert. Far from city lights, they set up their telescopes and scanned the sky. About 11 p.m., Bopp peered through Jim Stevens's 17.5-inch reflecting telescope at a star cluster catalogued as M70. Bopp spotted a peculiar glow at the edge of the view. The light source wasn't familiar, so he checked his sky charts and found that no object was known to be in that position. Astronomers, including thousands of amateurs around the world, know that a previously unknown comet can appear at any time, usually as a spot of light at a place in the sky where no other star is visible and no planet could be at the time. "Tom, you might have something," Stevens said to Bopp. The men watched the object for an hour as it moved across the field of view, and Bopp then drove home to report it by electronic mail to the International Astronomical Union in Cambridge, Mass. The IAU is the world center for collecting and disseminating reports of new discoveries in the heavens. "I never thought anything like this would ever happen," Bopp said later. Since the discovery, he has been interviewed extensively by media and has met many other celebrities of the astronomy world. "I'm having a blast with this." The comet would have borne his name alone had not the sky over New Mexico happened to clear that same night. Alan Hale, a professional astronomer and head of the Southwest Institute for Space Research in Cloudcroft, N.M., was a longtime comet watcher in his spare time, devoting one night a week to spotting known comets and measuring changes in their brightness. It had been rainy for a week in Cloudcroft, and Hale itched to get out and observe the sky. July 22 was his first clear night, so he set up his 16-inch reflector in his driveway. After checking on a known comet, Hale waited patiently for another to come in range. He decided to pass the time by observing M70, the same star cluster Bopp and his friends were viewing. Hale turned his telescope to M70 within minutes of the time Bopp had done the same. He spotted a faint object. "Since I had looked at M70 just two weeks earlier, I knew there were no other objects in that field," Hale said in a talk at the Jet Propulsion Laboratory in Pasadena, Calif. When he saw the glowing fuzz in the telescope -- a typical view of a distant comet -- Hale described how he felt: "I'll use an {Isaac} Asimov quote, That's funny.' " Hale made a sketch, estimated the object's brightness, went into his house, checked sky charts and found that no objects were known to be in that position. From his home computer, he logged into the IAU computer to see whether any known comets were in that part of sky. None existed. Finally, he sent a detailed e-mail message to the facility, explaining that he might have found a comet. Back at his telescope, Hale noticed that the object had moved. He watched it for another three hours until it set. It was then about 4 a.m., but, Hale said, he had trouble sleeping the rest of the night. The next morning, the IAU sent congratulatory e-mail messages to Hale and Bopp and sent a telegram to astronomers around the world, "Circular 6187." It said: "Comet 1995 01: Independent reports of the visual discoveries of a new comet have been received from Alan Hale and Thomas Bopp .... All observers note the comet to be diffuse with some condensation and no tail, motion toward the west-northwest .... Comet found while observing M70." The telegram added sky location details. Over the next few days, fresh visual confirmations poured into the Cambridge agency from Australia, Europe and Asia, all with similar data. With this information, the IAU calculated the comet's orbit and realized that the comet was very far away. The fact that it was visible in amateur telescopes suggested it had to be a very big object. The calculations also indicated that, when the comet moved closer to the sun, it could become spectacularly visible to the naked eye. Three days later, the IAU had given it another name: Comet Hale-Bopp. Blaine P. Friedlander is a freelance writer and author of the Skywatch column on the Style Plus page. TO LEARN MORE Everybody's Comet: A Layman's Guide to Hale-Bopp by Alan Hale. $12.95, High-Lonesome Books, Silver City, N.M., 162 pp.