Welcome to You Ask Andy

David Wester, age 11, of Tilley, Alta., Canada, for his question:

DOES THE AURORA MAKE CRACKLING NOISES?

The aurora is one of the most beautiful displays ever seen in the skies. In the far North, its soft shimmering colors seem to fill the whole heavens. Some observers report that an aurora also may be heard. This may be so, but it is not likely that the crackles are heard by human ears.

Sometimes the face of our glorious sun erupts in a rash of spots. These supersize sunspots are thought to be magnetic storms that stir up tremendous energies. Sometimes they shoot forth stupendous flares of seething gases. Streams of charged particles zoom far out into space and sometimes come plunging through the upper layers of the earth's atmosphere.

These high speed solar particles strike atoms and molecules in the thin air aloft, changing their electric charges. There is static, and sometimes complete blackouts in radio communications occur. However, one needs a radio set to hear these crackles.

The same event also may cause the upper atmosphere to act like a fluorescent tube. Then we see an aurora, shimmering like pale waving rainbows. The display occurs from 70 to several hundred miles above the earth. Even if it did produce audible crackles, we could not hear them from such a distance. To an observer on the ground, the gorgeous display takes place in total silence.

The auroras, alias the Northern and Southern lights, are centered around the earth's magnetic poles. These are the opposite ends of the mighty magnet inside the globe. Their magnetic force attracts the charged solar particles as they approach the earth. Though the most spectacular displays are in polar regions, sometimes they reach almost as far as the equator.

The most usual colors are fragile greens, though reds occur in polar regions. The most breathtaking aurora appears around the North or South Pole. It is a sunburst of darting arcs and arrows in ruby reds.  Farther from the poles, auroras come in hazy streaks, flickering fingers and pale waving curtains.

The air in the aurora zone is thin, though it contains atoms and molecules of oxygen and atoms of nitrogen. Atoms of oxygen emit the greens; nitrogen and molecules of oxygen emit the ruby reds. And, so far as we know, they perform these miracles with no audible sounds.

 

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