What are the Aurora Borealis?

The Aurora Borealis, also called the Northern Lights, are curtains of light created when fast electrons from the solar wind slam into the rarefied gas of the upper atmosphere. The mechanism of action is similar to the way electrons in a television generate specks of light when they impact the phosphor-coated inside of the screen. The physics of the phenomenon are complex, however, and not perfectly understood. The energy of certain types of aurora probably derives from a dynamo effect of the interplanetary (solar wind-caused) magnetic field against the Earth's magnetic field. This is similar to the way electricity can be generated by rotating a magnet within an electromagnetic coil.

The aurorae are green or faintly red, produced by re-emission from atmospheric oxygen. Atmospheric nitrogen sometimes produces very faint blue/violet aurorae. Some of the most magnificent pictures of the Aurora Borealis have been taken from the Space Shuttle or International Space Station, which views it from an angle impossible from the ground.

The Aurora Borealis is most easily observed about 1,500 miles (2,400 km) from the Earth's magnetic poles. A southern variant also exists, called the Aurora Australis, but this is rarely observed because it mainly occurs in the oceans around Antarctica. The Earth's magnetic poles are located about 11° away from the geographical poles, and in the north, the magnetic pole is located just north of Canada, meaning the lights are easily observable from places like Fairbanks, Alaska. Rarely, during magnetic storms and coronal mass ejections (super solar-flares), the phenomenon becomes much more intense, and it can be visible as far south as Boston. In 1856, a coronal mass ejection produced aurorae so strong that a person could apparently read a book at night in New York using the light produced.

The Northern Lights have long been subjects of mythology and superstition. Scandinavians once thought they were produced by the reflections of huge schools of herring, while in Scotland, they were called the "merry dancers." Gold miners in Alaska believed they were reflections of the greatest mother lode. Until the advent of scientific satellites, many of the theories about the aurorae were very speculative, and even today, the understanding of researchers is not perfect, but it is steadily improving.