The announcement date was chosen to coincide with both the anniversary of Herschel’s discovery of Uranus in 1781 and Percival Lowell’s birthday in 1855. Tombaugh told Slipher he had found Planet X, and on March 13, 1930, the Observatory announced the finding of the new object. He determined that the object had moved about 3 mm on the plates between the two exposures, indicating an orbital distance of about 40-43 AU, putting it outside the orbit of Neptune at about the right place to be the predicted planet. Finally, in February 1930, while scanning the plates he had taken a few weeks earlier, he saw something that moved. It was incredibly tedious work requiring intense concentration, but Tombaugh greatly preferred it to going back to work on the farm, so he persisted.Īfter months of searching, he had found several asteroids, but nothing that fit the criteria for Planet X. Most of the time the photos were the same and Tombaugh would see nothing, but if an object had moved between the two exposures, Tombaugh would see a blink. The device would present him with sections of the two photo plates to be compared, shifting between the two several times a second. Tombaugh used a device called a blinking comparator to make the comparison. Distant stars would appear in the same position on both plates, but a planet would have moved in the several days between the two exposures. He spent many cold nights in the unheated observatory dome carefully making the observations.Īfter creating many such pairs of plates, he would compare the two members of each pair. For each region, Tombaugh made two photos, taken several days apart. First, he had to use the telescope to make many photographic plates, systematically taking pictures of regions of the night sky where the new planet might appear. Slipher assigned the task to Tombaugh, who arrived in Flagstaff in January 1929. In 1927 the observatory was ready to resume the search for Planet X, and it acquired a new 13 inch refracting telescope for the search. Lowell searched for the planet, which he called Planet X, from 1905 to his death in 1916.įor years after Lowell’s death, the Lowell observatory was hampered by an expensive legal battle with Lowell’s widow. Lowell had observed some peculiarity in the orbits of Neptune and Uranus and figured there must be another planet with a mass comparable to Neptune’s orbiting the sun beyond Neptune. But as it became more and more clear that there was no evidence for that theory, he began to focus on searching for a new planet. Lowell, a businessman and astronomer known for his belief that a network of canals existed on Mars and was evidence of an intelligent alien civilization, built the Lowell Observatory to prove his theory. Planet X had been predicted by Percival Lowell. His task would be to search for “Planet X.” After a short correspondence, Slipher offered him a job at the observatory. Slipher, the director of the Lowell Observatory in Flagstaff, Arizona, asking for comments. When he was 20, Clyde Tombaugh began building his own telescopes.īy 1928 Tombaugh had built his third backyard telescope and used it to make drawings of Mars and Jupiter. The family soon ordered a better telescope to encourage their son’s interests. He became interested in astronomy as a teenager after observing craters on the moon and rings around Saturn through his uncle’s three inch telescope. The announcement in March of Pluto’s discovery was a moment of excitement for both scientists and the public.Ĭlyde Tombaugh was born on Februin Illinois, and grew up on a farm in Kansas. Tombaugh at the door of the Pluto discovery telescope, Lowell Observatory, Arizona In early 1930, Pluto was discovered by a farm boy from Kansas with no formal training in astronomy.
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