Dazzling Display Across the Area
If you can get outside tonight in a relatively dark area, you may be treated to one of nature's greatest spectacles- the aurora borealis- more commonly called the northern lights. They are seen infrequently in Chicago, about once every two years, so tonight is a great chance to view them.
This is an Ask Tom Why question from a few years ago explaining the northern lights.
Dear Mr. Skilling:
Why do some northern lights show color and at other times they shine only white? I've seen the northern lights many times but have witnessed only on rare occasions the colors so often associated with them.
Linda Turkovich, McHenry, Ill.
Dear Linda,
The northern lights (aurora borealis) are one of nature’s most spectacular shows. The light of the aurora is caused by a stream of electrons emitted from the sun (the “solar wind”) reaching the atmosphere of the earth and colliding with atmospheric gases. Auroral colors are determined by the energy levels of the incoming electrons as well as the density and composition of the atmosphere they are passing through. When struck by the electrons, these gases become excited and emit a characteristic color.
Nitrogen tends to give off a green color, while oxygen emits both red and green hues. Since our atmosphere is 78% nitrogen, green is the most common auroral color, and frequently in weaker auroras this green appears as the “whitish” color you describe. An exceptionally energetic aurora may be predominately red, and some auroras tend to appear purple or bluish just before dawn when sunlight strikes the top of the auroral rays in the high atmosphere hundreds of miles above the observer.
Copyright © 2004, WGN-TV
Steve Kahn
