TinWiki: Aurora Borealis

The Aurora Borealis, or Northern Lights, refers to the visible light that results when electrically charged particles (electrons and protons) from the sun, or solar wind, interact with the Earth's electrically charged magnetosphere. Some of these particles get trapped in the magnetosphere and travel along the Earth's magnetic field towards the north and south magnetic poles. As these particles strike atoms and molecules in the Earth's atmosphere (oxygen and nitrogen) energy is released, some of this energy is in the form of a visible aurora. The Aurora Borealis is seen only at night, most commonly in the polar zones.

Auroral Colors



Excited atoms produce light. Different gases within our Earth's atmosphere give off different light when they are electrically charged or "excited". At about 60 miles up in the atmosphere oxygen gives off the more common yellow-green color. The red auroras are a result of oxygen at higher levels of the atmosphere (about 200 miles up). Nitrogen produces the blue and red-purple colors of the aurora. Look at it this way, a neon light contains the gas, neon. When electricity is ran through the neon gas it excites the gas and gives off light. That light would be a red-orange.

Aurora Forms

An aurora's form is determined by it's level of activity.

• Homogeneous arc: The aurora at it's least active form. The curtain form is glowing, however diffuse and has no distinct structure.
  
• Rayed arc: When the aurora is slightly more active the curtain forms vertical stripes or rays.
  
• Active aurora: Produces moving swirls from 10 to 100 miles wide.
  
• Rising vapor column: This aurora can be several hundred miles long and gives the illusion that it is "touching" the horizon.
  
• Corona: Appears as rays shooting out in all directions.
  

Audible Auroras

The upper atmosphere is much too thin to carry sound waves, and sound would take about five minutes to travel to us, however, many witnesses have claimed to be able to hear a swishing and/or crackling sound, much like static electricity. This sound has been known to disappear when one closes their eyes so it may be a person's eyes playing tricks on them. That theory has yet to be proven.

Aurora Australis

Aurora activity occurs at both the north and south pole regions. Auroral activity in the southern hemisphere is referred to as the Aurora Australis, or Southern Lights.

Forecasting and Viewing

There are several things that directly affect one's chances to view the aurora. The level of geomagnetic activity, auroral activity and location.

The Kp Index

When the interaction between the solar winds and the Earth's magnetosphere is particularly violent, the border of the magnetosphere is pushed toward Earth. The KP Index places a value (0 - 9) on the earth's current geomagnetic activity. Multiple observatories collect data from magnetometer readings in near real-time then convert and post this data in 3-hour intervals. Magnetometers are capable of determining the strength of Earth's magnetic field as well as it's orientation and direction, in particular, how far south the magnetic field is pushed. The higher the Kp level, the stronger the disturbance and the further this disturbance is pushed toward the equator.

The magnetic disturbance on May 29, 2003 and into May 30, 2003 had a Kp Index of '8'. The aurora could be seen as far south as Virginia, U.S..

Magnetic Latitude

You will also need to know your magnetic latitude which you can then compare to the Kp Index assigned to that latitude. Basically, The closer that you are to the poles, the greater the chance of seeing the aurora.

Auroral Activity

Auroral activity is another indication of geomagnetic activity. As determined by the NOAA POES it applies data to an auroral activity table (1 - 10), 10 being most active.

Forecasting the Aurora

The National Oceanic and Atmospheric (NOAA) provides current auroral activity data at each pole.

Auroral Activity Extrapolated from NOAA POES

Auroras On Other Planets

In order for an aurora to take place on any planet or moon there must be an atmosphere and a magnetic field. For instance, Mars, Venus, and our moon do not have magnetic fields. Mercury nor our moon have an atmosphere so they do not have auroras. Auroras have been observed on Saturn, Triton, Titan, Jupiter, Io, Uranus and Neptune. It was thought that because Io does not have an atmosphere that it could not have an aurora. However, Io's active volcanoes can temporarily provide an atmosphere.

Folklore

North American Indians and Eskimos had many stories to explain the auroras.

• The Point Barrow Eskimos thought that the aurora was evil and carried knives to ward it off.
  
• The Fox Indians believed that the spirits of their slain enemies who were restless for revenge.
  
• The Greenland Eskimos believed that the auroras were the dancing spirits of dead children.
  
• The Mandan of North Dakota believed that the lights were the fires by which medicine men and warriors cooked their enemies in huge pots.
  

External Links

Geophysical Institute: Aurora FAQ's
Geophysical Institute: Auroral Forms
Space Weather
Space.Com: What is the Aurora?
NOAA: Auroral Activity
NASA: Aurora
University of Alaska/Fairbanks: Aurora Colors
Welcome to Alaska
Nordly's: Auroras on Other Planets
WebTribe: Legends and Folklore of the Northern Lights.
Geophysical Institute: Auroral Forecast

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