To the 95th anniversary of the discovery of Pluto

In 1781, the English astronomer W. Herschel discovered the sixth planet in the Solar System - Uranus. Due to deviations in the apparent motion of Uranus from the calculated orbit, in 1846 the seventh planet from the Sun - Neptune was discovered. But the deviations in the motion of the planets remained significant. Percival Lowell, based on the apparent disturbances in the motion of the planet Uranus, carried out extensive work on calculating the orbit for a new planet, which he called Planet X. He carried out his search observations at his own observatory in 1905-1916. However, he was unable to find this planet then. In January 1929, work on the search for a new planet was resumed. For this purpose, an astrograph with an aperture of 32.5 cm was specially ordered. And to work with this telescope, amateur astronomer Clyde Tombaugh was invited. To search for the planet, a special technique was developed, which consisted in photographing large areas of the sky near the point opposite the Sun, three images at intervals of several days. Comparing these images on a blink-comparator made it possible to find objects that had moved during this time. On February 18, 1930, in the photos taken on January 23 and 29, Tombaugh was able to detect a moving object. Its speed indicated that the object was outside the orbit of Neptune. On March 13, 1930, on the 75th anniversary of Lowell's birthday and the 149th anniversary of the discovery of Uranus, the then director of the Lowell Observatory, W. Slipher, announced the discovery of a new planet in the Solar System.