Sunlight reflecting off and interacting with the grooves on a records surface. The variation between the sides and bottom of the grooves are used to recreate music through induction and amplification in a player, the light produces constructive and destructive interference patterns via diffraction and reflection in the grooves. With the right equipment a laser can read them as well as a needle and cartridge. Feeling groovy? http://www.youtube.com/watch?v=TBQxG0Z72qM
