Auroras Offer Clues to Mysteries of Solar Activity

"The curious thing is that as they come from the sun, electrons in the solar wind have energies of only a few electron-volts," Hallinan says, referring to a unit of measure physicists use to describe particles' energy levels, and an amount of that unit that a nitrogen atom hardly finds exciting. "But a few hundred kilometers above the Earth, electrons have been measured with energies of 1,000 to 10,000 electron-volts. What's accelerating them?"

Another question researchers are pursuing involves the almost explosive features found in auroras. "Over the course of a minute or less, energy levels jump by a factor of 1,000," Hallinan continues. "It's as if the energy in the Earth's magnetic field gets dumped in one area. There's a lot of hand-waving" as people try to explain that phenomenon, he says.

Many questions remain

"We also see time variations that can be very dramatic to watch," Hallinan says. "In the early-morning hours you get cloud-like patches of pulsating aurora instead of glowing arcs. Why are things different before and after midnight? And every now and then we see a different vertical profile of luminosity - a bright band across the sky, with a weak band below it and another bright band on the bottom. That doesn't fit the models."

Perhaps these unsolved mysteries allow the scientists to retain their awe. Syun Akasofu, one of the field's pioneers and the Geophysical Institute's director, and his wife are known to head out in the dead of night to watch auroral displays.

Back at the Geophysical Institute, Hallinan's colleague Hans Stenbaek-Nielsen sums up the state of aurora studies. Despite the encyclopedia and textbook articles that seem to explain the phenomenon, "we do not understand what it's all about," he says. "Why do we see a single arc? Why do new arcs form? Why do aurora appear in arcs and curtains? Why do they appear as pulsating patches on the morning side? These are such basic parts of auroral displays that if you don't understand those, you don't understand aurora."

Web Sites Help Make Aurora-Hunting Easy

If you want to see an aurora, but don't have the time, money, or inclination to spend a week in Yellowknife, Northwest Territory - the self-proclaimed aurora capital of the world - don't despair.

As solar activity increases, so does the likelihood of spotting an aurora - even for people who don't live in Alaska or the northern expanses of Canada. On rare occasions, solar storms can be so intense that the aurora they spawn can be seen into the tropics. In 1989, a storm produced a red aurora that could be seen as far south as the Yucatan Peninsula.

The best viewing opportunities are on clear nights during the late fall, winter, and early spring. Plan to look from just before midnight to the predawn hours, although in places like Fairbanks, aurora can be seen as soon as it's dark.

Two Web sites can help you pick dates for aurora-hunting. The University of Alaska at Fairbanks maintains a site (dac3.pfrr.alaska.edu/~pfrr/AURORA) that publishes aurora forecasts, including a map. The Space Weather Operations Center, run by the National Oceanic and Atmospheric Administration, is another source (www.sel.noaa.gov/forecast. html). Look down the forecast for the "GEOMAGNETIC A INDICES," a measure of how active the earth's magnetic field is likely to be. A 25 or 30 means that people living in the northern tier of the lower 48 states have a good chance of seeing an aurora, even if it appears only as a glowing region of the northern sky. If the index exceeds 40, people as far south as Colorado may be able to see one.

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