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Seven Natural Wonders of the World:
Aurora

Auroras (north/south polar lights; or aurorae) are natural light displays in the sky, usually observed at night, particularly in the polar regions. They typically occur in the ionosphere. They are also referred to as "polar auroras". In northern latitudes, the effect is known as the aurora borealis, and it was named after the Roman goddess of dawn, Aurora, and the Greek name for north wind, Boreas by Pierre Gassendi in 1621.

The aurora borealis is also called the northern polar lights, as it is only visible in the sky from the Northern Hemisphere, the chance of visibility increasing with proximity to the north magnetic pole, which is currently in the arctic islands of northern Canada.

Aurorae seen near the magnetic pole may be high overhead, but from further away, they illuminate the northern horizon as a greenish glow or sometimes a faint red, as if the sun was rising from an unusual direction. 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.

Auroral Mechanism

Aurorae 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. 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 it connects 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.

Origin

The ultimate energy source of the aurora is the solar wind flowing past the Earth. The magnetosphere and solar wind consist of plasma (ionized gas), which conducts electricity. It is well known that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts across, rather than along, the lines of the magnetic field, an electrical current is said to be induced into that conductor and electrons will flow within it.

The amount of current flow is dependent upon a) the rate of relative motion and b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the direction of flow is dependent upon the direction of relative motion. Dynamos make use of this basic process ("the dynamo effect"), any and all conductors, solid or otherwise are so affected including plasmas or other fluids.

In Literature and Film

The aurora features prominently in Philip Pullman's Northern Lights, and in the film adaptation, The Golden Compass. Characters in the story can sometimes see glimpses of another universe through the lights.

The Northern Lights are featured in the Disney movie Brother Bear as the source of changes in the world. They are said to be the spirits of every living creature's ancestors.

The aurora sets the events of the 2000 film Frequency in motion.

Reference / Image Credits:
Wikipedia
1. Wikimedia
2. Wikimedia
3. James N. Sears
4. Wikimedia
5. Wikimedia
6. Wikimedia