Aurora Borealis
The Aurora, also known as the Northern Lights, has mystified people down through the ages, scientists, poets, and lay persons alike. Written records of so-called "great auroral displays" date back more than two thousand years.
Sometimes the Aurora over Alaska and other auroral zones is barely visible or appears colorless and unmoving. But at other times the auroras can be incredibly bright, multihued and fast moving. Tall green curtains of lights, red tipped at their bottoms, stretch from horizon to horizon. They ripple and sway, fold and unfold, then suddenly disappear, only to reform in a new shape minutes later.
For those who live in Alaska, the Aurora is a part of northern life. Fall, winter and spring is the special season for viewing the great lights for residents and off-season visitors. Some Alaskans have "Aurora Alerts;" when a display begins, the first person to spot them begins a phone tree to get the word out.
The "pulsating Aurora" is one form of Northern Light common during the post-midnight hours. It blinks on and off every few seconds as though controlled by some mysterious unseen hand in the sky flicking a switch.
The great auroral displays are spectacular global events during which the Aurora spreads down from the polar regions to cover as much as two thirds of the earth's skies with bright, fast-moving masses of light, often deep red in color.
The rare "great auroral displays" follow one or two days of violent solar flares in the vicinity of major sunspots. These solar flares cast out vast streams of electrically charged particles which stream down into the earth's atmosphere. These particles, mostly electrons and protons, are steered away from the tropical regions by the earth's magnetic field.
Striking the gases of the earth's high atmosphere, the charged particles glow. It is exactly the same thing that happens in a television tube: complex streams of electrons within the TV strike the phosphor coated face of the tube, and cause it to glow, creating the colored moving patterns we see from our living room couches. Outside, at night, we can look up at that great star-studded television tube in the sky; if the Aurora is out and no clouds are about, the colored patterns will be there too.
| Even though "great auroral displays" appear infrequently, spectacular displays of Aurora are common in Alaska and other auroral zone locations. This is because the sun is always sending out a stream of electrons and protons. They make up the solar wind which blows constantly toward the earth and other planets. |
| Enough of the solar wind particles come into the earth's high atmosphere at the auroral zone to create continuous Aurora, summer, winter, fall and spring.Although much is known about the Aurora, this fascinating phenomenon still withholds some of its mysteries. For example, scientists do not yet understand why the Aurora is so highly structured. For the University of Alaska Fairbanks, this continues to be an important area of study. The most beautiful Aurora is composed of thin sheets that stretch upward a hundred miles or more and extend across the sky from horizon to horizon, like gigantic ribbons set on edge high above and parallel to the earth's surface. These arcs and bands whip and weave across the sky, and bright rays ripple along them at fantastic speed. Some of these intricate multicolored forms have a thickness of only 100 meters, about the length of a football field, yet may be several hundred kilometers tall and well over 1,000 kilometers in length. It boggles the mind to realize—as has been proven by simultaneous observation in the two hemispheres—that these sharply defined auroral forms have an identical or nearly identical mate in the southern hemisphere, out of sight and almost a world away. Joined together by an invisible magnetic bond that arches far above the Equator, each pair of mated auroral dancers move across the cold polar skies in perfect harmony. Each motion or brightness change in one hemisphere is mirrored in the other, on a time scale of less than a fraction of a second. A most curious and highly controversial question involves auroral sound. Although I've never heard one, my wife has and so have several scientists I know. Some reports of hearing noises associated with auroral displays may be erroneous impressions, but I am convinced many others are not. Hundreds of written reports indicate noises are sensed when a particular type of fast-Aurora is nearly overhead. Some people sense whistling and crackling noises, even when they close their eyes. The reports of auroral sound make it certain that the unknown cause of the apparent sound is in the vicinity of the hearer, not in the Aurora itself. Most likely, the reported noises are related to electrical phenomena which accompany certain types of bright Aurora. No matter how many auroras one may have seen, a good high-latitude display, as seen in Alaska, sends tingles up the viewer's spine. Even a moderate display seen at the auroral zone in the 49th state can be far more exciting to watch than one of the rare "great displays." The best of words and photographs fail to capture the magnificence of the high-latitude Aurora, although some of Robert Service's poetry may come close. |