John Fairbanks, age 16, of Helena, Mont., for his question:
WHAT CAUSES AN AURORA?
An aurora is a luminous atmospheric phenomenon that occurs most frequently above 60 degrees north or south latitude, but also in other parts of the world. It is named specifically, according to its location, aurora borealis (Northern light) or aurora auetralis (Southern light). The term aurora Polaris (polar light) is a general name for both.
Auroral displays probably occur when protons and electrons are shot from the sun, striking the earth's upper atmosphere. The earth's magnetic field directs the particles toward the magnetic poles.
As the particles move, they collide with atmospheric particles and change their electrical charge. They glow much like the charged particles in a fluorescent tube. The result is a beautiful display of glowing or flickering natural light seen at night in the sky. Aurora borealis and australis occur moat frequently in far northern and far southern areas. Light displays have been seen in the northern United States and as far south as Mexico. Most of them occur in September and October, and in March and April.
Auroral displays usually take place about 70 miles above the earth's surface and are sometimes 150 miles in height.
There are many kinds of auroral displays. Some extend in an arc for hundreds of miles. Long, thin rays form curtains of light. Green is the most commonly seen color during a display. It is caused by atomic oxygen. The red colors are caused by molecular oxygen and nitrogen.
Auroral displays appear to be most frequent at the time of greatest sunspot activity. Sunspots affect the zone in which the displays occur. The zone shifts toward the Equator at the time of maximum sunspot frequency and toward the poles when the sunspots are at a minimum. The displays seem to be associated with magnetic storms.
The auroral display assumes an endless variety of forms besides the auroral arch, which is a luminous arc lying across the magnetic meridian. There's also the auroral band which is generally broader and much more irregular than the arch.
Sometimes the display features filaments and streamers at right angles to the arch or band. There's also the corona, a luminous circle near the zenith and auroral clouds, indistinct nebulous masses which may occur in any part of the heavens.
The auroral glow is a luminous appearance high in the sky with filaments diverging toward the zenith. And to round out the wide variety of forms you'll find fans, flames, streamers of various shapes and curtains.
Aurora was named for the goddess of dawn in Roman mythology. She's the one who opened the gates of heaven for the sun god every morning. The ancient Greeks called her Eon. She and the mortal, Tithonus, had a son, Memnon. Morning dewdrops on the grass are the tears Aurora shed when Memnon was killed at Troy. Aurora also loved the hunter Orion and she restored his sight. She is said to also be the mother of the winds.