Aurora over Lake Inari, Finland

Aurora over Lake Inari, Finland

Lake Inari is the largest lake in Sápmi and the third-largest lake in Finland. It is located in the northern part of Lapland, north of the Arctic Circle. The lake is 117–119 meters (384–390 ft) above sea level. The freezing period normally extends from November to early June.

The aurora borealis, also known as the northern lights, occurs in an upper layer of Earth’s atmosphere called the ionosphere, but they typically originate with activity on the Sun. Occasionally, during explosions called coronal mass ejections, the Sun releases charged particles that speed across the solar system. 

Auroras are produced when the Earth's magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. [Wikipedia]

Solid Colored Aurora

Green is common at the upper latitudes, while red is rare. On the other hand, aurora viewed from lower latitudes tend to be red.

Element Emission Colors

Oxygen: The big player in the aurora is oxygen. Oxygen is responsible for the vivid green (wavelength of 557.7 nm) and also for a deep brownish-red (wavelength of 630.0 nm). Pure green and greenish-yellow aurorae result from the excitation of oxygen.

Nitrogen: Nitrogen emits blue (multiple wavelengths) and red light.

Other Gases: Other gases in the atmosphere become excited and emit light, although the wavelengths may be outside of the range of human vision or else too faint to see. Hydrogen and helium, for example, emit blue and purple. Although our eyes cannot see all of these colors, photographic film and digital cameras often record a broader range of hues.

Aurora Colors According to Altitude

Above 150 miles: red, oxygen

Up to 150 miles: green, oxygen

Above 60 miles: purple or violet, nitrogen

Up to 60 miles: blue, nitrogen

NASA - About Aurora

https://www.nasa.gov/science-research/heliophysics/auroras/

https://pwg.gsfc.nasa.gov/polar/EPO/auroral_poster/aurora_all.pdf

The Colors of the Aurora (National Park Service)
https://www.nps.gov/articles/-articles-aps-v8-i1-c9.htm

Image Credit: Role Bigler
Release Date: Sept. 9, 2024

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