Celestial Mechanics

Twentieth century physics have found that photons of light possess momentum which, when they are absorbed or reflected by material bodies, transfers momentum to the bodies, producing a light pressure effect. The interaction of photon velocity of light with the orbital velocities of bodies orbiting the Sun produces a retarding effect on their orbits known as the Poynting-Robertson Effect. These effects are insignificant for large solar system bodies, but are important for bodies smaller than 0.394 in (1 cm) in diameter. The Poynting-Robertson Effect causes such small interplanetary particles to spiral inwards towards the Sun and to eventually be vaporized by heating from its radiation. Much smaller (micron-sized) particles will be pushed out away from the Sun by light pressure which, along with electromagnetic forces, are the dominant mechanisms for the formation of comet tails.