What is an absorption spectrum?

(N/A) When white light,which contains all wavelengths of the visible spectrum,is passed through a cool gas,the atoms of the gas absorb specific wavelengths of light that correspond to the energy transitions of their electrons.
As a result,these specific wavelengths are missing from the transmitted light,appearing as dark lines against a continuous bright background in the spectrum.
This pattern of dark lines is known as the absorption spectrum of the material of the gas.