An aurora is a natural light display in the sky, predominantly seen in the high latitude regions. The name ”auroras” is now more commonly used for the linguistic plural ”aurorae” of ”aurora”, so is adopted throughout the main text of this article. Modern style guides recommend that the names of meteorological phenomena, such as aurora borealis, be uncapitalized. Auroras are caused by charged particles, mainly electrons and protons, entering the atmosphere from above causing ionisation and excitation of atmospheric constituents, and consequent optical emissions. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.