The last planet of the solar system - Pluto was discovered by astronomer Tombaugh February 18, 1930.
Strictly speaking, Pluto is no longer considered a planet, it was decided in 2006 to classify Pluto as a dwarf planet, such as the largest asteroid Ceres, Pluto's moon Charon, or.
The reason for the decision on Pluto to the reckoningdwarf planet became adopted by the same Assembly in 2006 criteria that determined the cosmic body belongs to a class of planets. One of them is that the orbit of the planet can not cross another object, and Pluto's orbit crosses Neptune.
Pluto is one of those planets,whose existence was first confirmed by calculation and then it was fixed telescope. To determine the size of distant planets and the distances to them the laws of Kepler and Newton used. With the help of Kepler's laws proved that the orbits of the planets are not form a perfect circle. Newton's laws define the interaction of the two planets on the basis of their mass and their distance from each other. The greater the mass of the planets, the more they attract each other, the smaller the distance between them, the greater the effect on them the force of attraction. On the basis of these laws, the scientists calculated the estimated orbit of Uranus movement, which at that time was considered the last planet of the solar system, however, monitor its movement revealed that her real orbit coincides with the calculated value. Then some scientists expressed the view that for Uranus have not yet opened a planet that their attraction has an effect on the orbit of Uranus. This planet was Neptune, which was discovered by the Berlin Observatory.
However, the attraction of Neptune is not fully explainedstrangeness in Uranus motion. In 1915, the American Percival Lowell hypothesized that beyond Neptune there is another unknown planet, which also affects the orbit of Uranus, and have to be found it in any part of the sky, 15 years later, in 1930, the new planet was discovered by studying pictures of the sky, the sky is the area covered by Lowell.</ P>