Pluto discovered
Pluto once believed to be the ninth planet is discovered at the Lowell Observatory in Flagstaff Arizona by astronomer Clyde W.Tombaugh.The existence of an unknown ninth planet was first proposed by Percival Lowell who theorized that wobbles in the orbits of Uranus and Neptune were caused by the gravitational pull of an unknown planetary body.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.
His finding was confirmed by several other astronomers and on March 13 1930the anniversary of Lowells birth and of William Hershels discovery of Uranusthe discovery of Pluto was publicly announced.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.Plutos 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.After its discovery some astronomers questioned whether Pluto had sufficient mass to affect the orbits of Uranus and Neptune.
In 1978 James Christy and Robert Harrington discovered Plutos only known moon Charon which was determined to have a diameter of 737 miles to Plutos 1428 miles.Together it was thought that Pluto and Charon formed a double-planet system which was of ample enough mass to cause wobbles in Uranus and Neptunes orbits.In August 2006 however the International Astronomical Union announced that Pluto would no longer be considered a planet due to new rules that said planets must clear the neighborhood around its orbit.
Since Plutos oblong orbit overlaps that of Neptune it was disqualified.
