Aurora and artificial airglow The aurora is rising behind us. - B. Springsteen Airglow is caused by photon emission from high altitude atmospheric atoms and molecules excited by the ambient electrons and chemical reactions at high altitude; the aurora is caused by precipitating electrons, and sometimes protons, that ionize atoms and molecules and excite ions, atoms and molecules in the upper (85-500 km) atmosphere. The atoms, molecules and ions in excited states can lose energy by collisional de-excitation, chemical reactions or emission of radiation. The precipitating particles that cause aurora dissipate their energy at different altitudes depending on their initial energy and pitch angle. Due to the varying composition of the upper atmosphere, the relative amplitude of the emissions varies depending on the initial energy of the precipitating particles. The optical spectra from the aurora and airglow are rich in lines and bands of emission in the visible and near visible wavelengths. In this chapter the characteristics of the lines measured by ALIS will be presented.