Photographer Wade B. Clark, Jr., © 2000. 35mm Canon F1 set on a tripod, 28mm wideangle f1.8 lens, Fuji NHG II 800 speed color print film, and about a 20-second exposure via cable release.
Aurora borealis of August 11-12, 2000, over Mount Baker, east of Bellingham, Washington, viewed from Baker Lake.
We know much more than Lewis and Clark did about what causes the northern lights, but questions remain. In short, scientists believe they have figured out what happens to cause the beautiful sight, but they still are studying the mechanics of how it occurs.1
Most importantly, we at least understand that the northern lights are a natural, regular function of our solar system.
From the sun, a continuous flow of charged atomic particles—the solar wind—travels throughout our solar system. The sun itself undergoes a cycle of activity that spreads over more than 22 earth years. At the beginning of the cycle, there are fewer sunspots—darker and cooler places on the sun's surface (which may be caused by alterations in the sun 's magnetic field). Then, over the next 11.1 years on average, more and more sunspots appear until they reach peak activity. Sunspots become fewer and fewer during the rest of the approximately 22-year cycle.
Associated with sunspots are solar flares, which are brief but strong eruptions of radiation. Carried by the solar wind, the radiation reaches the edge of earth's atmosphere about two days after the solar flare can be observed by telescope. When the radiation enters earth's ionosphere, it interrupts radio signals sent by people around the earth. Our planet's ionosphere is an outer layer of atmosphere, holding very few molecules and subatomic particles, which reaches from about 49 to 310 miles above earth's surface. At about 50 to 60 miles up, cosmic rays and solar radiation regularly split oxygen molecules into ions and free electrons—subatomic particles that carry electric charges. Because it reflects radio rays, the ionosphere is what makes radios work, most of the time. Solar flares interrupt radio transmission.
Also around any astronomical body is a magnetosphere, a field whose own magnetic force, rather than the planet's, is in control. When radiation from a solar flare reaches earth, the magnetosphere captures the charged particles and somehow directs them down through the ionosphere toward the magnetic pole. In the northern hemisphere, the magnetic north pole is over the southern tip of Greenland, not at the geographical North Pole.
As Lewis and Clark and their sergeant stood outdoors at Fort Mandan watching the northern lights, they were seeing a solar flare's radiation pass through the ionosphere, flowing toward magnetic north. When this concentrated burst of solar radiation hit still-whole oxygen and nitrogen molecules, it split masses of them all at once. The subatomic particles . energy escaped in wavelengths that caused certain colors to appear as light moving in its .infinite forms . far up in the cold November sky.2
But part of the energy that causes auroras may come from earth itself. Research published in January 2003 suggests that movements in earth's magnetic field also may send electrons into our atmosphere.3 Andreas Keiling of the University of Minnesota, and the Center for Space Research on Radition, at Toulouse, France, published an analysis of a year's worth of data collected by NASA's POLAR satellite.
Looking at ripples in the Alfven waves (movements in the magnetic field) at 15,500 to 23,560 miles altitude, the group concluded that those waves created enough energy to throw electrons into earth's atmosphere. Keiling wrote that, "One third of the energy [of auroras] could be driven by these waves." Scientists still don't know why the Alfvén waves occur, though.
As research continues, it is worthwhile to look back to Norway in about 1230 A.D. A book called The King's Mirror collected current knowledge—just as Owen did five hundred years later—written in the form of a father answering his son's questions about the physical world, governments, and how to live. Beginning an explanation of the aurora borealis, the author wrote:
". . . it is the same with the northern lights as with anything else we know nothing about, that wise men put forward ideas and simple guesswork, and believe that [which] is most common and probable."
Scientists continue to study the phenomenon of the aurora borealis not only on our own planet but throughout our solar system,4 hoping to replace the old somehows and maybes with a more believable explanation.
1. Sources for this page include multiple articles in Encyclopaedia Britannica and World Book Encyclopedia.
2. Red, blue, and yellowish-green are the colors seen in earth's aurora borealis.
4. Auroras have been observed on Jupiter, Saturn, Uranus, and Neptune, planets that have low atmospheric densities compared to earth's, and are composed mostly of helium and hydrogen.