Editing Pluto (section)

=== Discovery ===
{{further|Planets beyond Neptune}}
[[File:Pluto discovery plates.png|left|thumb|alt=The same area of night sky with stars, shown twice, side by side. One of the bright points, located with an arrow, changes position between the two images.|Discovery photographs of Pluto]]
In the 1840s, [[Urbain Le Verrier]] used [[Classical mechanics|Newtonian mechanics]] to predict the position of the then-undiscovered planet [[Neptune]] after analyzing perturbations in the orbit of [[Uranus]]. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranus's orbit was being disturbed by another planet besides Neptune.<ref>{{cite book |last=Croswell |first=Ken |title=Planet Quest: The Epic Discovery of Alien Solar Systems |url=https://books.google.com/books?id=60sPD6yjbVAC |location=New York |publisher=The Free Press |year=1997 |isbn=978-0-684-83252-4 |page=43 |access-date=April 15, 2022 |archive-date=February 26, 2024 |archive-url=https://web.archive.org/web/20240226151141/https://books.google.com/books?id=60sPD6yjbVAC |url-status=live }}</ref>

In 1906, [[Percival Lowell]]—a wealthy Bostonian who had founded [[Lowell Observatory]] in [[Flagstaff, Arizona]], in 1894—started an extensive project in search of a possible ninth planet, which he termed "[[Planet X]]".<ref name="Tombaugh1946" /> By 1909, Lowell and [[William Henry Pickering|William H. Pickering]] had suggested several possible celestial coordinates for such a planet.<ref name="Hoyt" /> Lowell and his observatory conducted his search, using mathematical calculations made by [[Elizabeth Langdon Williams|Elizabeth Williams]], until his death in 1916, but to no avail. Unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7, 1915, but they were not recognized for what they were.<ref name="Hoyt" /><ref name="Littman1990" /> There are fourteen other known [[precovery]] observations, with the earliest made by the [[Yerkes Observatory]] on August 20, 1909.<ref name="BuchwaldDimarioWild2000" />

[[File:Clyde W. Tombaugh.jpeg|left|thumb|upright|Clyde Tombaugh, in Kansas]]

Percival's widow, Constance Lowell, entered into a ten-year legal battle with the Lowell Observatory over her husband's legacy, and the search for Planet X did not resume until 1929.{{sfn|Croswell|1997|p=50}} [[Vesto Melvin Slipher]], the observatory director, gave the job of locating Planet X to 23-year-old [[Clyde Tombaugh]], who had just arrived at the observatory after Slipher had been impressed by a sample of his astronomical drawings.{{sfn|Croswell|1997|p=50}}

Tombaugh's task was to systematically image the night sky in pairs of photographs, then examine each pair and determine whether any objects had shifted position. Using a [[blink comparator]], he rapidly shifted back and forth between views of each of the plates to create the illusion of movement of any objects that had changed position or appearance between photographs. On February 18, 1930, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and 29. A lesser-quality photograph taken on January 21 helped confirm the movement.{{sfn|Croswell|1997|p=52}} After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the [[Harvard College Observatory]] on March 13, 1930.<ref name="Hoyt" />

One Plutonian year corresponds to 247.94 Earth years;<ref name="Pluto Fact Sheet" /> thus, in 2178, Pluto will complete its first orbit since its discovery.