Pluto, once believed to be the ninth planet, is discovered at the Lowell Observatory in Flagstaff, Arizona, by astronomer Clyde W. Tombaugh on 18th February 1930.
The existence of an unknown ninth planet was first proposed by Percival Lowell. Lowell calculated the approximate location of the hypothesized ninth planet and searched for more than a decade without success. However, in 1929, using the calculations of Powell and W.H. Pickering as a guide, the search for Pluto was resumed at the Lowell Observatory in Arizona. On February 18, 1930, Tombaugh discovered the tiny, distant planet by use of a new astronomic technique of photographic plates combined with a blink microscope.
With a surface temperature estimated at approximately -360 Fahrenheit, Pluto was appropriately given the Roman name for the god of the underworld in Greek mythology. Pluto’s average distance from the sun is nearly four billion miles, and it takes approximately 248 years to complete one orbit. It also has the most elliptical and tilted orbit of any planet, and at its closest point to the sun it passes inside the orbit of Neptune, the eighth planet.
In August 2006, however, the International Astronomical Union announced that Pluto would no longer be considered a planet.
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