"I've found Planet X." Clyde Tombaugh, the discoverer of the planet Pluto, died recently. He was born in Illinois in 1906, and later spent his adolescence on the family farm near Burdett, Kansas, exploring the universe with homemade telescopes. Later he was hired by Lowell Observatory near Flagstaff, Arizona after sending the staff some sketches he had made of Mars and Jupiter of which he was wanting an opinion. Its director, V. M. Slipher, was so impressed that he immediately hired him for the work of exposing photographic plates in a new planet search program that the observatory's late founder, Percival Lowell, had begun in 1910. Slipher's instructions to the 24-year old farmer were to expose 14-by-17-inch plates, each containing upwards of a million stars, in Gemini where Lowell's last calculations had given that region as the likely place in which his "Planet X" might be lurking. Tombaugh began his search on April 11, 1929, making exposures of a particular area one night and than repeating an exposure five or six days later. After a like pair were taken, the professional staff set about using a blink comparator (a device which used an electromagnet to flip a small mirror back and forth in order to rapidly redirect light from one plate to another and thus cause a moving object to jump forward and back). Nothing was found on the plates and Slipher went on to other research while the plates quickly accumulated. By early summer, as the rainy season approached, the director assigned Tombaugh the blink task. After months of searching he had found several dozen asteroids but no Planet X. Tombaugh remarked that it was "the most tedious work I had ever done...I was in a state of despair." He noted that the asteroid points he had found shifted very little from one plate to the next, and after pondering the problem he realized that he needed to search regions only near the opposition point, since any orbiting body beyond the Earth would be photographed than during is most rapid retrograde motion. That fall he began chasing the opposition point through Aquarius and Pisces and by January he had returned to Gemini. He exposed two plates of the region near Delta Geminorum on January 23 and 29 and after finishing the task of blinking plates of Taurus that he had taken earlier, he reached for the Gemini plates late on the afternoon of February 18. "I raised the eyepiece assembly to the next horizontal strip," Tombaugh related. "At the center line, I had the guide star Delta Gem in the small rectangular field of the eyepiece. After scanning a few fields to the left, I turned the next field into view. Suddenly I spied a fifteenth magnitude image popping out and disappearing in the rapidly alternating views. Then I spied another image doing the same thing about 3 millimeters to the left. 'That's it,' I exclaimed to myself." The young amateur ran down the hall to Slipher's office and announced, "I've found Planet X. I'll show you the evidence." Amazingly, as was discovered some time later, the new planet had been overlooked in photographs taken at Mt. Wilson eleven years earlier. Those 1919 images had been missed because of plate defects in one and because Planet X had been swamped by a nearby star in the other. Although several names were suggested for the new planet, among them Zeus, Constance (Mrs. Lowell), Cronos, and Minerva, Pluto was chosen since it was the god of the gloomy underworld and it recalled the name Percival Lowell. As Tombaugh recalled of Mrs. Lowell's visit to the observatory that summer, while still dressed in mourning black, "She came eager to meet the young man who had discovered 'my husband's planet.'" During his search, he had photographed 65 percent of the sky and spent 7,000 hours examining about 90 million star images. Later, Dr. Tombaugh earned degrees from the University of Kansas and Northern Arizona University. He concluded his career as an astronomy pro- fessor at New Mexico State University. Besides Pluto, his discoveries included six star clusters (5 open and 1 globular), a supercluster of galaxies stretching from Andromeda to Perseus, one comet, a nova in 1932, and about 775 asteroids. Tombaugh possessed a rich, keen sense of humor. He relished his remark when the Smithsonian Institution asked if it could have for its museum the telescope he had made in 1928, built with parts of the farm cream separator and the crankshaft from his father's 1910 Buick, saying, "I told them I was still using it." Of the decades he had devoted to research, he said, "I've really had a tour of the heavens." David Levy, his friend and biographer, said of his passing, "Until the end, Clyde was an incredibly interesting person to be around. Famous for his puns, his command of the intricacies of the English language was astonishing. On January 17, 1997, astronomy lost one of its most colorful figures. If planet Pluto were sentient, it would take note of the loss of the man who unveiled its existence to our world almost 67 years ago." Few have seen so much of the universe in such minute detail. John Leppert Deneb Observatory Sarles, ND 58372-9618 48o56'07"N 99o09'40"W =============================================================== John Leppert Deneb Observatory 48o56'07"N 99o09'40"W: 31 Jan 1997 14:30 CST