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An aurora is a natural light display in the sky (from the Latin word aurora, "sunrise" or the Roman goddess of dawn), predominantly seen in the high latitude (Arctic and Antarctic) regions.[nb 1] Aurorae are caused by cosmic rays, solar wind and magnetospheric plasma interacting with the upper atmosphere (thermosphere/exosphere). Their charged particles, mainly electrons and protons, enter the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent light emissions. Auroras caused by protons are sometimes referred to as proton arcs.[2][3] Incidental protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.
Most auroras occur in a band known as the auroral zone,[4] which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the auroral oval, a band displaced towards the nightside of the Earth.