A qualitative description of the development of a typical auroral display as the result of an electrical discharge in the ionosphere is presented. The prime cause of the discharge is taken as the potential difference existing between points in the interplanetary medium as a result of an interaction between charged particles of solar origin and the earth's magnetic field. The characteristics of the occasional very intense aurorae visible over large areas of the earth are discussed, as well as the normal diurnal and seasonal variation of auroral occurrence. The origin of the electric field is discussed, and a possible explanation in terms of particles trapped in the earth’s magnetic field, is presented.