The various lines in the atomic spectra are produced when electrons
jump from higher energy state to a lower energy state and photons are
emitted These spectral lines are called emission lines But when an atom
absorbs a photon that has precisely the same energy needed by the
electron in a lower energy state to make transitions to a higher energy
state, the process is called absorption Thus if photons with a continuous
range of frequencies pass through a rarefied gas and then are analysed
with a spectrometer, a series of dark spectral absorption lines appear in
the continuous spectrum