The Northern Lights
People for millennia have enjoyed the beautiful and often eerie curtains of light in the nighttime sky known as the aurora. Auroras are glowing streaks in the sky seen at night in the far north and south. They are popularly called northern lights (officially called "Aurora borealis" in the northern hemisphere, and "Aurora australisis" in the southern). During this luminous meteoric phenomenon, colorful light appears in streams, ascending toward the zenith from a dusky line or bank, a few degrees above the polar horizon; when reaching south beyond the zenith, it forms what is called the corona, a spot in the heavens toward which the dipping needle points. Occasionally the aurora appears as an arch of light across the heavens from east to west. Sometimes it assumes a wavy appearance, and the streams of light are then called merry dancers.
"Aurora Borealis", the scientific name of the aurora of the northern hemisphere, means "northern dawn". Originating in an atmospheric layer high above the surface of the earth, the northern lights can be seen during dark hours in the northern hemisphere.
The light is emitted when charged particles from the sun are guided by the earth's magnetic field into the atmosphere near the poles. When the particles contact atmospheric molecules, primarily oxygen and nitrogen, at altitudes from 300 down to 100 km, a part of the energy of the collisions transforms to visible light.
People on earth only see a small part of their display, as the lowest sections of the Aurora are 40 miles up. Astronauts looking down on the polar region from space have a better overall view to observe the Aurora as it extends approximately 600 miles above the earth.
Also it seems that the aurora is not limited to Earth, there is one picture that I found of the aurora on Saturn in the photos section.
Extreme Scientific Explanation
Charged particles, mostly protons and electrons are constantly emitted from the outer region of the Sun (corona) and reach the magnetosphere of Earth having a velocity of some 350 to 400 kilometers per second. Magnetosphere is the space around the Earth pervaded by its magnetic field. The charged particles flow around the comet-shaped magnetosphere and form eddies and distortions behind the obstacle. Electrons and protons collide with the gas particles in the outer atmosphere (altitude between 100 to 500 km). A small part of the collision energy is used for excitation of electrons in the gas particles -- mainly nitrogen molecules and oxygen atoms. The excited electrons return to their ground states by emitting light of distinct wavelength and thus a distinct color. The wavelength of the light depends on the electronic structure of the particle itself and on the energy of the charged particle colliding with the atom or molecule. Oxygen atoms emit green light at high collision energies and red light at lower energies, whereas nitrogen molecules emit blue and violet light. Green polar light can be observed in the altitudes around 100 to 200 km as only particles with high energy can penetrate into the lower layers of the atmosphere, the red light is formed in higher altitudes of 200 to 500 km due to lower energies of the colliding electrons.
The particles, which stream down the magnetic field of the Earth, reach the neutral atmosphere in a rough circle called the auroral oval. This circle, or annulus, is centered over the magnetic pole and is around 3000 km in diameter during quiet times. The annulus grows larger when the magnetosphere is disturbed. The location of the auroral oval is generally found between 60 and 70 degrees north and south latitude.
Color of excited atoms
The aurora is caused by the interaction of high-energy particles (usually electrons) with neutral atoms in the Earth's upper atmosphere. The strongest auroras are quite bright, comparable to moonlight. The aurora occurs only above altitudes of 80 km and infrequently above 500 km. The average altitude for normal intensity aurora is between 110 and 200 km. This process is similar to the discharge in a neon lamp.
Entirely red northern lights sometimes may be seen, particularly at low latitudes. In earlier times, people often mistook this red light for fire on the horizon. Any particular color of the aurora depends on a specific atmospheric gas and its electrical state, and on the energy of the particle that hits the atmospheric gas. Atomic oxygen is responsible for the two main colors of green (wavelength of 557.7 nm) and red (630.0 nm). Nitrogen causes blue and deep red hues.
Auroral features come in many shapes and sizes. Tall arcs and rays start brightly 100 km above the Earth's surface and extend upward along its magnetic field for hundreds of km. These arcs or curtains can be as thin as 100 meters while extending from horizon to horizon. Auroral arcs can nearly stand still and then, as though a hand has been run along a tall curtain, the aurora will begin to dance and turn. After midnight, the aurora can take on a patchy appearance and the patches often blink on and off once every 10 seconds or so until dawn.
Most of the auroral features are greenish yellow but sometimes the tall rays will turn red at their tops and along their lower edge. On rare occasions, sunlight will hit the top part of the auroral rays creating a faint blue color. On very rare occasions (once every 10 years or so) the aurora can be a deep blood red color from top to bottom. In addition to producing light, the energetic auroral particles deposit heat. The heat is dissipated by infrared radiation or transported away by strong winds in the upper atmosphere.
(There are pictures of the Aurora, both from Earth and from Space in the photos section.)
Aurora Myths and Legends
Many legends, myths and superstitions have revolved around the aurora throughout the history of mankind. The early dragon legends of China and Europe are said to have originated from the aurora. Some cultures, especially those at high latitudes, have regarded the sighting of the aurora as a sign of royal birth; to others it suggests ghosts of the dead or the precursor for war. The Aboriginals of Scandinavia, the Sámi, believed that the northern lights had supernatural powers to resolve conflicts and had auroral symbols on their magic drums. Up until the Enlightenment of the 18th century, the northern lights often were viewed with fear or reverence and were related to contemporary concepts of heaven and hell.
In Norse mythology, a bridge named Bifrost connected Earth and Åsgard, the home of gods. It most likely was modeled after rainbows or the northern lights, and was guarded by the god Heimdal. Popular belief in Scandinavia linked the aurora to dead women, especially to dead virgins. In China the aurora was believed to predict forthcoming births. Also from Norse mythology are the valkyries. Valkyries are any of Odin's handmaidens who conducted the souls of slain warriors to Valhalla. It is said that their armor sheds a strange flickering light, which flashes up over the northern skies when they are on their errand of bearing souls to the realm of the dead.
The oldest descriptions of the aurora are from the Mediterranean countries and from ancient China. At most, people in these temperate regions would have seen the aurora only once or twice in their lives. In the 6th century BC, Ezekil, a profit-priest of ancient Israel, saw the aurora and wrote that "…a whirlwind came out of the north, a great cloud, and a fire enfolding itself, and a brightness was about it, and out of the midst thereof as the color of amber, out of the midst of the fire." (Old Testament of the Bible, Ezekil 1:4).
The Tlingits and Eyak Indians of Southeastern Alaska consider them a sure sign of impending battle and that someone would be killed when they put on their cosmic light display.
In the Norwegian folklore, the aurora has been described as a harbinger of harsh weather: snow and wind are believed to follow bright displays.
The only Eskimo group that considered the Aurora an evil thing was the Point Barrow Eskimos. They believed this so deeply, that they used to carry knives to keep it away.
Eskimo peoples in the Hudson Bay area of North America, and elsewhere, are naturally very much aware of auroral phenomena. A common belief among the Eskimos is that the aurora can be attracted by whistling to it, while a handclap will cause it to recede. Other Eskimo beliefs suggest that spirits playing a game of celestial football with the skull of a walrus produces the aurora. (One group, on Nanivak Island, suggested that a human skull was, indeed, used by walrus spirits!).
Some tribes of North American Indians believed the aurora to be the light of lanterns carried by spirits seeking the souls of dead hunters. Like the Point Barrow Eskimos, Fox Indians in Wisconsin feared the aurora, seeing in it the ghosts of their dead enemies. Other tribes perceived the aurora as the light of fires used by powerful northern medicine men.
In ancient Roman and Greek records, references may sometimes be found to 'chasmata' in the sky, the auroral arc structure being regarded in such instances as being the mouth of a celectial cave. The term isochasms is used nowadays to relate two geographical points that share an identical frequency of auroral occurrence.
Interesting Links
~Click this link now, don’t ask why, just do it. These are some BEAUTIFUL photos.
http://spaceweather.com/aurora/gallery_06nov01.html
Live video of many of the different effects created by the aurora.
http://www.northern-lights.no/english/pages/experience/intro.shtml
~One main source used, also has info on other lights/colors in the sky phenomenon.
http://webexhibits.org/causesofcolor/4B.html
~Another source used, has a great gallery of photos.
http://www.everythingalaska.com/aurora1.html
~Wonderful photos including time-lapse mpegs for you to download and view.
http://www.pfrr.alaska.edu/~pfrr/AURORA/INDEX.HTM
~Very extensive list of links to various aurora related sights.
http://northernlightsnome.homestead.com/Links.html
~View the aurora forecast as well as other space weather.
http://www.spaceweather.com
~Another source used for auroral myths.
http://www.oulu.fi/~spaceweb/textbook/aurora/folklore.html>
Art based on and inspired by the Aurora Borealis
http://www.ristoklint.com/stock_art_7/g7_p7.htm
Northern Lights art for kids, tells some ideas on how to help your child create the Northern Lights.
http://www.teelfamily.com/activities/northernlights/art.html
Click archive on this page to see some of the paintings.
http://www.northern-lights.no/english/pages/events/intro.shtml
My favorites so far…these are some excellent paintings. Be sure to let the bottom one come up, I love that one ;)
http://www.streetmorrisart.com/northernlightsartgalleryI.html
This page will take a while to load, but even if its just to see the first two prints on this page its worth it.
http://www.diannehendrix.com/Northern%20Lights.htm
Photos
All photos are © their respective owners, they were not taken by me, and I claim no owner ship of them, please visit the sites above, thanks!
Click on the thumbnail to see the full size image.
