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In the beginning of 1376, the town of Altkirch in Alsace was about to be attacked by a Gugler company – a gang gathered from some of the worst cutthroats of France. As the citizens of Altkirch manned the walls, waiting for the battle to begin, the night sky was suddenly filled with colored lights. The people of Altkirch, being convinced that this sign from the heavens was also a sign form Heaven itself, took the offensive and routed the Guglers. The colored lights in the sky that saved the day for Altkirch was almost certainly a display of an aurora. The shimmering colored lights that appear at a location north of the equator such as those seen over Altkirch are called the Aurora Borealis, while those seen from south of the equator are the Aurora Australis.
People during the Middle ages believed an aurora was the result of a battle in the sky. The rustling or swishing noise that sometimes accompanies an aurora was explained as the sound of weapons clashing between two celestial armies.
An aurora display is one sky event which places a skygazer from the most northernly latitudes (or the most southernly for those south of the equator) at a distinct advantage. The closer you are to a pole, the more likely that you will see an aurora. Alaska and Scotland are ideal locations for observing aurora, although at some times they can be seen well south of the U.S.-Canadian border. An aurora is produced by the same solar wind, which is also responsible for comet tails. When the charged particles of the solar wind reach the Earth, they are captured by the Van Allen belts, which are two doughnut-shaped rings surrounding the Earth and extending thousands of miles beyond the planet's surface. The doughnut holes are located near the north and south magnetic poles.
The north magnetic pole is located in Canada's Hudson Bay. The Van Allen belts normally collect the solar wind and let the excess particles that they are unable to contain fall through the doughnut hole and create an aurora. The spillover creates a small oval-shaped area from which an aurora is seen. At night the oval-shaped area usually extends to 59 degrees north latitude but at time of heavy solar wind, the oval can extend to 39 degree north latitude and make it possible to see an aurora anywhere in the northern continental United States. The colored lights of the aurora are created by collisions between the charged particles originating from the Sun and molecules of air. Electrons are knocked off the air molecules and when the electrons recombine with the molecules, energy is emitted as different colored lights.
Auroras can not be predicted in advance, but SkyWatch subscribers receive notices of increased solar activity, which might be a prelude to the appearance of an aurora.
The best time for gazing at an aurora is on a moonless night although it can sometimes produce as much light as a full Moon. You might see a greenish or greenish-yellow arc looking somewhat like a rainbow with a fuzzy upper edge and sharp lower edge. An arc will occasionally turn into a ray, which is like a giant searchlight, either greenish-yellow or red. Another auroral variation is a curtain, which tends to have a greenish-bluish color and appears like heavy curtains hanging down from the sky. Sometimes an auroral display will appear to pulse rhythmically, while others will look like violet or rose-colored clouds. These are just a few types of auroras that may be seen. The best portrayal of an aurora that I’ve come across is that shown I the movie "Local Hero" starring Burt Lancaster. It also has a nice meteor shower in it.