In astronomy, an aurora is a luminous phenomenon that consists of streamers, arcs, or ripples of dancing vibrant light that appear in the upper atmosphere of a planet's magnetic polar regions. Auroras on planet Earth have been found to be caused by energetically charged particles that travel from the sun to the Earth on solar wind, and are then magnetically drawn to the poles. Once there, they begin to collide and interact with gaseous atoms and molecules, and visible energy is released in the collisions, which gives observers an aural light show. Auroras in the northern hemisphere are known as aurora borealis, or northern lights; in the southern hemisphere, they are called aurora australis, or southern lights.
In Latin, aurora means "dawn," and in Roman mythology, Aurora is the personification of dawn. (The Greek counterpart is Eos, whose name also means "dawn.") In Late Latin, borealis means "of the north," so aurora borealis literally translates as "dawn of the north." Its polar opposite, australis, means "of the south," giving rise to the name aurora australis, "dawn of the south." Both phenomenon are similar in their dazzling light shows made up of colors interacting in various forms, including vibrant rippling curtains, waving arcs, shimmering bands, and shooting rays. The colors of the lights—which range from red, blue, and purple to green and yellow—depend on which gaseous molecules (mainly oxygen or nitrogen) collide with the solar particles as well as at what altitude that interaction takes place.
The aurorae are generated by the solar wind—a stream of charged particles travelling from the outer layer of the sun, or corona, and slamming into Earth's magnetic field. This acts like a shield around the planet that deflects most of the particles. But at its weakest points around the poles, some can penetrate into the upper atmosphere, where they collide with and excite gas molecules. As these molecules de-excite, they release the photons of light that make the aurorae. The type of excited molecule, along with the altitude of the collisions, determine the colour of the aurorae.
— Abigail Beall, The New Scientist, 7 Dec. 2019