Atomic absorption and emission spectra both measure the same thing but in different ways. Both measure the difference in electron orbital energy levels for a given atom. Since this energy difference is a discrete amount for a given atom, the energy readings are depicted as lines on the spectrum of light wavelengths. The big difference between the two is how the energy is obtained. Absorption spectra are obtained by irradiating the atoms with a wide range of electromagnetic radiation and the wavelengths that are absorbed by the sample are recorded as lines on the spectrum. Emission spectra are obtained by heating the sample (usually with a flame) to give the atoms extra energy. As the energy is dissipated, photons are given off and recorded as lines on the spectrum. The important thing to remember is that the lines for both types of spectra are located at the same positions since the energy amount is the same whether it is being absorbed or emitted.