The last planet of the Solar System - Pluto, was discovered by the astronomer Tombo on February 18, 1930.
Strictly speaking, Pluto can no longer be considered a planet, in 2006 it was decided to classify Pluto as dwarf planets, such as Ceres's largest asteroid or Pluto's moon Charon.
The reason for the decision to assign Pluto toDwarf planets were adopted at the same assembly in 2006, the criteria by which the belonging of the cosmic body to the class of planets is determined. One of them is that the orbit of the planet can not cross another object, and the orbit of Pluto is intersected by Neptune.
Pluto belongs to the number of those planets,The existence of which was first confirmed by calculations and only then it was fixed by a telescope. To determine the size of distant planets and the distance to them, the laws of Kepler and Newton are used. With the help of Kepler's laws it is proved that the orbits of planets do not have the form of a regular circle. Newton's laws determine the interaction of two planets on the basis of their mass and their distance from each other. The greater the mass of planets, the stronger they are attracted, the smaller the distance between them, the greater the force of attraction acting on them. Based on these laws, scientists calculated the supposed orbit of the Uranus movement, which was then considered the last planet of the solar system, but observations of its movement revealed that its real orbit does not coincide with the calculated one. Then some scientists expressed the opinion that beyond Uranus there is not an open planet yet, which by its attraction has an impact on the orbit of Uranus. This planet was Neptune, which was discovered by the Berlin Observatory.
However, the attraction of Neptune did not fully explainStrangeness in the movement of Uranus. In 1915 the American Percival Lowell hypothesized that there is another unknown planet behind Neptune that also affects the orbit of Uranus, and indicated in which part of the sky it should be searched, in 15 years, in 1930 a new planet was discovered by studying Photographs of the starry sky, in the very area of the sky indicated by Lowell.