Max Planck first defined blackbody radiation in the 19th century. Blackbody radiation is the thermal electromagnetic radiation emitted from an opaque body in thermodynamic equilibrium with its environment that has a continuous spectrum dependent only on the body's temperature. Planck received the Nobel Prize in 1918 for his work on blackbody radiation, which helped establish quantum theory by proposing that electromagnetic energy can only be emitted or absorbed in discrete quanta.