Transcript: German physicist Gustav Kirchhoff experimented with hot gases in the laboratory in the mid-nineteenth century and deduced three laws of radiation that apply to all astronomical objects in space. The first is that a hot gas or sufficiently hot solid will emit with a continuous spectrum of radiation or a continuum. The second is that a hot gas will emit only certain bright wavelengths of radiation called emission lines. Each element emits its distinct and unique set of emission lines. The third is that a cool gas, when placed between the observer and a hot source of continuous radiation, will absorb certain wavelengths of light also corresponding uniquely to each element. These are called absorption lines.