All substance emit heat radiation. [5]
Measure the temperature of a body from the electromagnetic radiation which it emits in the
form of radiant heat, which is infra-red radiation and, if its temperature is high enough,
visible light. [9]
Different substances at different temperatures radiate energy at different rates. [5]
A body which completely absorbs any heat or light radiation falling on it is known as a black
body (black bodies only exist in theory).