On Thursday, March 29, a massive solar flare, associated with one of the largest sunspot groups ever seen on the sun, erupted. These highly energetic events contain large numbers of electrically charged particles (electrons, protons, etc.) and can wreak significant electrical effects upon the Earth's environment after the day or two it takes them to make the journey to Earth (provided they are ejected into our general direction). Such effects can include disruptions of radio communications and even, as has happened on rare occasions, disruptions of electrical power grids.

One of the most spectacular effects, at least from the point of view of an Earthbound sky-watcher, is the aurora borealis, or the so-called "northern lights" (the southern hemisphere's equivalent being the aurora australis, or "southern lights"). The charged particles from the solar flare ionize -- i.e., strip the electrons from the atoms of -- the gases in the Earth's atmosphere. When the electrons recombine with the atoms, they give off light, and it is this light that we see as the aurora. It is essentially the same phenomenon that goes on in a fluorescent light tube, which glows when an electrical current is applied to it; in the case of an aurora, it is the charged particles from the solar flare that supply the current.

Since, in the form of the solar wind, there is always a stream of charged particles arriving at the Earth, displays of the aurora are an almost nightly phenomenon at far northerly and southerly latitudes. However, when strong solar flares arrive at Earth the dramatically increased numbers and strength of the charged particles create the potential that aurora displays will be visible from latitudes much farther away from the poles. Since the March 29 flare was headed in Earth's direction there thus seemed to be a significant possibility that an aurora might be visible from fairly far south.

Aware of the reported flare, this author initially looked for an aurora display during the early evening hours on Friday, March 30, but didn't see anything. However, when he was commencing his planned astronomical observation program around 11:00 P.M. he immediately noticed a vivid red glow shining throughout the entire northern sky. After dutifully awakening his family, for the next hour and a half this author watched the ever-changing sky show; brilliant shafts of light would appear and disappear, and the lurid red glow almost seemed to be pulsing as it would appear brilliantly in one section of the sky, only to fade and then grow bright somewhere else. This is only the fourth aurora display that this author has witnessed during the more than thirty years that he has lived in southern New Mexico, and it was unquestionably the most magnificent.

Although we have a reasonably good understanding of the processes involved in producing an aurora from a solar flare, there are many, many factors involved, not all of which we understand completely or can predict with exact certainty. For example, about one day after the March 29 solar flare another flare erupted from the same sunspot group, and thus there was a possibility of additional aurora displays on the nights after March 30. However, in response to this flare the Earth's magnetic field switched direction -- in effect, reversing the electrical current -- and thus there was no repeat of the March 30 aurora.

Whenever we deal with complex systems with many interacting factors, we always have uncertainty when we try to predict later outcomes. Such systems are usually said to be "chaotic," a term which refers to the fact that even small changes in some of the initial factors can cause significant effects later on.

One example of such a chaotic system with which we're all familiar is the weather. It is true, of course, that with weather satellites and advanced computer modeling weather prediction is far more accurate that it was a half-century ago. Nevertheless, we can all attest to occasions when the weather we experienced was significantly different from that that was predicted. This inability to predict outcomes of chaotic systems like the weather is sometimes described under the somewhat whimsical name of the "butterfly effect," for example: when we predicted the weather for New York, we forgot to take into account the effects created by the flapping of a butterfly's wings in Tokyo. Although such an example appears ridiculously extreme, it illustrates the concept that even tiny differences in the initial conditions of a complex system can cause entirely disproportionate subsequent changes in that system.

One area of significant current interest where it might be worthwhile to consider this "butterfly effect" is in the discussion of the greenhouse effect and global warming. We understand the basic processes going on, and -- thanks in part to our studies of the planet Venus -- some of the potential outcomes. We are also able to measure the effects that we are producing by our continued emission of greenhouse gases into the atmosphere, and a recent detailed study by an international scientific panel strongly indicates that we are setting ourselves up for dramatic atmospheric changes in the not-too-distant future.

Are we able to predict with absolute certainty what will happen? Of course not; there are many variables within the system, not all of which we understand (or may even be aware of), and we cannot predict just what the effects of all these, interacting with each other, will be. All we can do is apply the knowledge we have, and make predictions on that basis. Somewhere in there, however, a butterfly may be lurking, but we don't know where it is, or what it might do.

Despite the uncertainty, it is nevertheless prudent to make plans based upon the knowledge we have and, if necessary, adjust our actions accordingly. After all, those who missed the March 30 aurora display will probably get another chance sometime in the future. But we may not get a second chance with Earth.

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