Aurora Borealis

Throughout time, humans have gazed at the sky to behold the splendor of the universe and contemplate the unknown. Certain times of the year, at the polar zones of Earth, there is a majestic show of lights and colors that occurs in the night sky. The lights that are viewed from the north skies are called aurora borealis, a combination of the name of the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas. The aurora borealis is visible only in the northern skies and is thus also known as the northern lights. This phenomenon also occurs in the southern skies; the counterpart is known as the aurora australis, with the name being derived from the Latin word for “of the South.”

The cause of these great lights starts far away from Earth, at the center of our solar system. The solar corona is the outermost portion of the sun and also the portion that produces temperatures that range in the millions of degrees. This corona, at times, ejects a rarefied flow of hot plasma (a gas consisting of both free and positive electrons) into outer space. This ejection of plasma is known as the solar wind. The solar wind travels through space until it nears Earth.

Earth's magnetosphere consists of the area dominated by its magnetic field. Extending far beyond Earth's atmosphere into outer space, the magneto-sphere blocks much of the solar wind and causes it to disperse. Solar winds contribute energy and material to the magnetosphere, causing the electrons and ions present in the magnetosphere to become energized. Once energized, these particles move along the magnetic field lines toward the polar regions of the atmosphere. The light is emitted shortly after this transfer occurs and is usually dominated by a greenish glow, produced by emissions of atomic energy, and also a dark-red glow, especially at high altitudes and lower energy levels. These two colors represent transitions of electrons and atomic energy, in absence of newer collisions, which continue for extended periods of time and account for the fading and brightening that occur. Other colors, such as purple and blue, can be seen when atomic energy and molecular nitrogen interact, but these displays tend to be of shorter duration.

The aurora borealis, or northern lights, shines above Bear Lake, Alaska. The lights are the result of solar particles colliding with gases in Earth's atmosphere. Early Eskimos and Indians believed different legends about the northern lights, such as they were the souls of animals dancing in the sky or the souls of fallen enemies trying to rise again

Source: U.S. Air Force photo by Senior Airman Joshua Strang.

[Page 65]The best place to see the aurora is near Earth's magnetic poles. It can, however, be seen in temperate latitudes during times of heavy magnetic storms. These storms relate directly to the 11-year sunspot cycle and are strongest during the peak. These strong storms can continue to occur for up to 3 years following the peak. In September 1859, one of these strong magnetic storms occurred and produced what is thought to be the most spectacular aurora ever witnessed in recorded history. The aurora was the result of the Carrington-Hodgson white light solar flare, which was emitted on September 1, 1859. This flare was one of the most intense coronal mass ejections in recorded history. The aurora was seen across the United States, Japan, Australia, and Europe. It was this aurora that allowed the link to be seen between auroral activity and electricity. Many of the telegraph lines that were in use across North America and Canada encountered interference during this aurora. Several other telegraph lines had been powered down but, nevertheless, they picked up a geomagnetically induced current through the lines and allowed the telegraph operators to continue communicating. Since then, the phenomenon of the aurora has continued to intrigue many people. In the future, scientific research in outer space may shed more light on the aurora phenomenon.

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