An aurora, sometimes referred to as a polar light, is a natural light display in the sky, predominantly seen in the high latitude regions. Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. Very high in the ionosphere (above 300 km or 180 miles), oxygen is the most common atom, and collisions there can create a rare red aurora. The strong yellow-to-green light that is most common is produced by collisions with oxygen at lower altitudes, between 100 and 300 km. Around 100 km, nitrogen molecules produce a red light that often seems to form the lower fringes on aural curtains.