Recently the 100th anniversary of the experimental discovery of light pressure effect was celebrated. After many attempts to measure this effect during several centuries this discovery was succeeded in the early XXth century in Russia, by P.N. Lebedev (1866-1912), Professor of Moscow University. His successful experiment and astronomical aspects of the light pressure effect theory obtained by him can be regarded as the foundation of Photogravitational Celestial Mechanics. The history of light pressure effect investigation in astronomy and physics beginning with Johann Kepler's ideas and hypothesis about comet tail shapes up to James Maxwell's theoretical prediction of this slight natural force value and then up to its P.N. Lebedev's successful measurement is presented. P.N. Lebedev, a disciple of A.Kundt, A.Stoletov and N.Umov, was a famous Russian physicist. He studied in Moscow, then, at Strasburg University, at a very good physical school of Prof. Kundt. Then he returned to Russia to Moscow University to work at Prof. Stoletov and Prof. Umov. All his short life was devoted to light pressure discovery and theory of light improvement. The history of Photogravitational Celestial Mechanics principles and ideas development is discussed. The main sections of Photogravitational Celestial Mechanics are determined for two kinds of high area-to-mass ratio (of the so-called high sailness) objects: small dust-and micrometeoroid particles in the Solar System and, alternatively, such large artificial constructions in space as solar sail spacecrafts and Earth satellites - inflatable balloons. It is shown that this new branch of Celestial Mechanics, photogravitational astrodynamics of artificial Earth satellites and solar sailing theory included, can be regarded now as an important part of modern Celestial Mechanics.