In addition to the aurora borealis in the northern hemisphere there is also the aurora australis, sometimes called the Southern Lights, in the southern hemisphere. The aurora australis is created the same way as the aurora borealis and it has the same appearance of dancing, colored lights in the sky. The best time to view the aurora australis is from March to September because the Antarctic Circle experiences the most darkness during this period. The aurora australis is not seen as often as the aurora borealis because they are more concentrated around Antarctica and the southern Indian Ocean.
How the Aurora Borealis WorksThe aurora borealis is a beautiful and fascinating occurrence in the Earth's atmosphere but its colorful patterns begin with the sun. It occurs when highly charged particles from the sun's atmosphere move into the Earth's atmosphere via solar wind. For reference, solar wind is a stream of electrons and protons made of plasma that flow away from the sun and into the solar system at around 560 miles per second (900 kilometers per second) (Qualitative Reasoning Group).
As the solar wind and its charged particles enter the Earth's atmosphere they are pulled toward the Earth's poles by its magnetic force. While moving through the atmosphere the sun's charged particles collide with the oxygen and nitrogen atoms found in the Earth's atmosphere and the reaction of this collision forms the aurora borealis. The collisions between the atoms and charged particles occur around 20 to 200 miles (32 to 322 km) above the Earth's surface and it is the altitude and type of atom involved in the collision that determines the color of the aurora (How Stuff Works).
The following is a list of what causes the different auroral colors and it was obtained from How Stuff Works:
- Red - oxygen, over 150 miles (241 km) above the Earth's surface
- Green - oxygen, up to 150 miles (241 km) above the Earth's surface
- Purple/violet - nitrogen, over 60 miles (96 km) above the Earth's surface
- Blue - nitrogen, up to 60 miles (96 km) above the Earth's surface
In addition to the lights being these various colors, they also appear to flow, form various shapes and dance in the sky. This is because the collisions between the atoms and the charged particles are constantly shifting along the magnetic currents of the Earth's atmosphere and the reactions of these collisions follow the currents.
Predicting the Aurora BorealisToday modern technology allows scientists to predict the strength of the aurora borealis because they can monitor the strength of the solar wind. If the solar wind is strong auroral activity will be high because more charged particles from the sun's atmosphere will move into the Earth's atmosphere and react with the nitrogen and oxygen atoms. Higher auroral activity means that the aurora borealis can be seen over larger areas of the Earth's surface.
Predictions for the aurora borealis are shown as a daily forecasts similar to weather. An interesting forecasting center is provided by the University of Alaska, Fairbanks' Geophysical Institute. These forecasts predict the most active locations for the aurora borealis for a specific time and give a range showing the strength of auroral activity. The range begins at 0 which is minimal auroral activity that is only viewed at latitudes above the Arctic Circle. This range ends at 9 which is maximum auroral activity and during these rare times the aurora borealis can be seen at latitudes much lower than the Arctic Circle.
The peak of auroral activity typically follows an eleven year sunspot cycle. During times of sunspots the sun has very intense magnetic activity and the solar wind is very strong. As a result the aurora borealis is also normally very strong at these times. According to this cycle the peaks for auroral activity should occur in 2013 and 2024.
Winter is usually the best time to view the aurora borealis because there are long periods of darkness above the Arctic Circle as well as many clear nights.
For those interested in viewing the aurora borealis there are some places that are best for viewing them frequently because they offer long periods of darkness during the winter, clear skies and low light pollution. These locations include places like Denali National Park in Alaska, Yellowknife in Canada's Northwest Territories and Tromsø, Norway (Layton).
Importance of the Aurora BorealisThe aurora borealis has been written about and studied for as long as people have been living in and exploring the polar regions and as such they have been important to people since ancient times and possibly earlier. For example, many ancient myths talk about the mysterious lights in the sky and some medieval civilizations feared them as they believed that lights were a sign of impending war and/or famine. Other civilizations believed the aurora borealis was the spirit of their people, great hunters and animals like salmon, deer, seals and whales (Northern Lights Centre).
Today the aurora borealis is recognized as an important natural phenomena and every winter people venture into northern latitudes to watch it and some scientists devote much of their time to studying it. The aurora borealis is also considered one of the Seven Natural Wonders of the World.