Aurora Borealis

The Aurora Borealis, also commonly known as the northern lights, are a natural light display in Earth's sky, mostly viewed in high-latitude regions. The auroras display dynamic patterns of brilliant lights 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 the solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magneto spheric plasma which are mainly electrons and protons, they precipitate into the upper atmosphere. The resulting ionization 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 of the precipitating particles. Planets, brown dwarfs and comets also have auroras.

Colours and the wavelengths of auroral light,

Red is observed at highest altitudes, excited atomic oxygen emits at 630 nm red; low concentration of atoms and lower sensitivity of eyes at this wavelength make this colour visible only under more intense solar activity. Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.

Green appears at lower altitudes, the more frequent collisions emit at 557.7 nm green. A fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common.

Red and green can also mix together to produce pink or yellow hues. The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains.

Blue is seen at even lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm blue being dominant.

Blue and Purple emissions, are typically viewed at the lower edges of the curtains, show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.

Ultraviolet radiation from auroras has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter, and Saturn.

Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.

The earliest depiction of the aurora may have been in Cro-Magnon cave paintings of northern Spain dating to 30,000 BC.

The oldest known written record of the aurora was in a Chinese legend written around 2600 BC. On an autumn around 2000 BC, according to a legend, a young woman named Fubao was sitting alone in the wilderness by a bay, when suddenly a 'magical band of light' appeared like 'moving clouds and flowing water', turning into a bright halo around the Big Dipper, which cascaded a pale silver brilliance, illuminating the earth and making shapes and shadows seem alive.

The term aurora borealis was coined by Galileo Galilei in 1619, from the Roman Aurora, goddess of the dawn, and the Greek Boreas, god of the cold north wind.