Aurora Borealis / Educational Video. NASA Connect - DITNS - Aurora Borealis. This work is licensed under a Creative Commons Attribution 2.5 License. NASA Connect Segment exploring the Aurora Borealis or Northern Lights. This segment exlains this natural phenomena and its history. Year: 2004. Keywords: Aurora Borealis; Northern Lights; Artificial Aurora; Terrella; Magnetism; Earth; Electrons; Natural Phenomena; Plasma; Solar Wind; Light Particles; Atmospheric Gases; Duration: 00:04:39; Sponsor: NASA; Contributing Organization: NASA. Auroras (North/South Polar Lights; or aurorae, sing.: aurora) are natural colored light displays in the sky, usually observed at night, particularly in the polar zone. They typically occur in the ionosphere. Some scientists call them "polar auroras" (or "aurorae polares"). In northern latitudes, the effect is known as the aurora borealis, named after the Roman goddess of dawn, Aurora, and the Greek name for north wind, Boreas. It often appears as a greenish glow or sometimes a faint red, as if the sun was rising from an unusual direction. The aurora borealis is also called the northern polar lights, as it is only visible in the North sky from the Northern Hemisphere. The aurora borealis most often occurs from September to October and from March to April. The Cree call this phenomenon the Dance of the Spirits. Its southern counterpart, the aurora australis/southern polar lights, has similar properties. Australis is the Latin word for "of the South". Benjamin Franklin first brought attention to the "mystery of the Northern Lights." He theorized the shifting lights to a concentration of electrical charges in the polar regions intensified by the snow and other moisture. Auroras are produced by the collision of charged particles from Earth's magnetosphere, mostly electrons but also protons and heavier particles, with atoms and molecules of Earth's upper atmosphere (at altitudes above 80 km). The particles have energies of 1 to 100 keV. They originate from the Sun and arrive at the vicinity of Earth in the relatively low-energy solar wind. When the trapped magnetic field of the solar wind is favourably oriented (principally southwards) it reconnects with Earth's magnetic field, and solar particles enter the magnetosphere and are swept to the magnetotail. Further magnetic reconnection accelerates the particles towards Earth. The collisions in the atmosphere electronically excite atoms and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most aurorae are green and red emission from atomic oxygen. Molecular nitrogen and nitrogen ions produce some low level red and very high blue/violet aurorae. The light blue colors are produced by ionic nitrogen and the neutral nitrogen gives off the red and purple color with the rippled edges. Different gases interacting with the upper atmosphere will produce different colors, caused by the different compounds of oxygen and nitrogen.
Tags: aurora borealis northern lights magnetism electrons solar wind plasma light particles earth atmosphere gases science USA
