Thursday, March 11, 2010
Northern polar lights
Auroras, sometimes called the northern and southern (polar) lights or aurorae (singular: aurora), 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, 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, with the chance of visibility increasing with proximity to the North Magnetic Pole. (Earth's is currently in the arctic islands of northern Canada.) Auroras 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 were rising from an unusual direction. The aurora borealis most often occurs near the equinoxes. The northern lights have had a number of names throughout history. The Cree call this phenomenon the "Dance of the Spirits." In the Middle Ages the auroras have been called a sign from God (see Wilfried Schröder, Das Phänomen des Polarlichts, Darmstadt 1984). Its southern counterpart, the aurora australis or the southern polar lights, has similar properties, but is only visible from high southern latitudes in Antarctica, South America, or Australasia. Australis is the Latin word for "of the South.". Auroras can be spotted throughout the world and on other planets. It is most visible closer to the poles due to the longer periods of darkness and the magnetic field.