These electrons and protons enter in collision with the neutral particles of the atmosphere, which then become excited and emit light. The colour and altitude of auroras provide a lot of information on the atmospheric gases that become excited. Below an altitude of 100 km altitude, nitrogen is responsible for the blue (picture 2) and red auroral lights (picture 3). From 100 to 250 km, approximately, green colour (often prevalent) is produced by the oxygen atoms. Above 250 km, the red light, which also results from the excitation of oxygen atoms, dominates the auroral emissions.

Auroras are generally visible in areas close to the poles (picture 4), forming an oval band around the magnetic North and South Poles. In the south, the auroral oval can be found above the Antarctic. In the north, the auroral oval crosses Alaska, Canada and the northern part of Scandinavia. However, at times of strong solar activity, auroras can sometimes be visible in areas of lower latitudes and in particular in Belgium (video 2). Auroras occurring in the northern hemisphere are called boreal auroras and auroras occurring in the southern hemisphere are called austral auroras. They are often identical in both hemispheres, like mirror images: this phenomenon is called combined auroras.