Aurora

aurora

A faint visual phenomenon associated with geomagnetic activity that is visible mainly in the high-latitude night sky. Aurora often occur within a band of latitudes known as the auroral oval, the location of which is dependent on geomagnetic activity. Aurora are a result of collisions between atmospheric gases and precipitating charged particles (mostly electrons) guided by the geomagnetic field from the magnetotail. Each gas (oxygen, nitrogen molecules and atoms) emits a particular color depending on the energy of the precipitating particles and the atmospheric composition, which varies with altitude. Typical aurora are 100–250 km above ground level. The colors of the aurora are normally both red and green. The red color occurs at heights around 250 km and is due to a specific transition of atomic oxygen; deeper penetrating particles (to around 100 km) interact with molecular nitrogen and oxygen causing green bands. Aurorae in the Northern Hemisphere are called aurora borealis ("northern lights") and in the Southern Hemisphere, aurorae are known as aurora australis. Patterns and forms of aurora include quiescent arcs, moving rays, patches, and veils.

Space Weather Prediction Center, 2018: Aurora. Accessed 13 August 2018. Available at https://www.swpc.noaa.gov/phenomena/aurora.

Term edited 13 August 2018.

Measure of the effective concentration of a chemical in the gas or liquid phase.

1. A measure (or condition) of height, especially of great height, as a mountain top or aircraft flight level.