Don Machholz, 26, grinds eyeglass lenses for an optical lab by day, sacks in from 9 p.m. to midnight and from then until dawn comes the excitement in his life. Don does not go to his local disco but rather to Loma Prieta Mountain, 17 miles from his Los Gatos, Calif. home, to search the heavens with his portable telescope. Last September 12, after 691 nights of sky-watching, he thought he had found his quarry: a previously unknown comet. "I had to go home not knowing," he recalls of his anxious wire to the Smithsonian Astrophysical Observatory for confirmation. The next night Machholz returned to the mountain and, eureka, at 4 a.m. saw that his find had, as he hoped, moved 1° south. "I was excited," he exults. "I knew I had indeed discovered one." Don's reward was the $250 check given U.S. amateurs by telescope distributor Roger Tuthill, but what counted was that the International Astronomical Union has named it after him: Comet Machholz 1978L (the letter "L" signifies it is the 12th found that year). He earned the honor. Hooked on star-gazing since he bought his first telescope at 13, Machholz is a junior college grad with only one astronomy course under his belt (and, surprisingly, no bags under his eyes). Comet Machholz 1978L won't return for another 1,000 years, but the red-headed sky watcher doesn't care. He's back on the mountain these nights, seeking a '79 vintage.