An aurora (pl. aurorae or auroras) is a natural light display in Earth's upper atmosphere caused by charged particles from the Sun colliding with atoms in the atmosphere. These collisions excite oxygen and nitrogen, which then emit light of different colours such as green, red, and purple. When observed in high-latitude regions they are called polar lights and aurora polaris. In the Arctic they are called the northern lights or aurora borealis; in the Antarctic, the term southern lights or aurora australis is used. Auroras display dynamic patterns of radiant light that appear as curtains, rays, spirals or dynamic flickers covering the entire sky. Auroras are the result of disturbances in the Earth's magnetosphere caused by enhanced speeds of solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magnetospheric plasma. These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/exosphere). The resulting ionization and excitation of atmospheric constituents emit light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Other planets in the Solar System, brown dwarfs, comets, and some natural satellites also host auroras.
