In a NY Times article about the Grail mission to the moon (see http://tinyurl.com/84dc5ew), the last paragraph states: But if part of the core is still molten, as is currently thought, the sloshing will delay the deformation to slightly after the closest approach. The effect is so tiny that the scientists will first have to account for effects like the pressure of light from the Sun pushing on the Moon. Does light (photons) exert a pressure? Sunlight consists of much more than pure light (photons). It is a stream of particles which have mass that can understandably exert a pressure. Therefore, is the writer mistaken?