Jannie Slingerland, age 12, of Diamond City, Alberta, Canada, for her question:
What are those light beams in the winter sky?
Surely they riust be the ghostly fingers of aurora borealis, alias the Northern Lights. Sometimes these beams and far more gorgeous displays appear in the skies above Canada and parts of the United States. People who live farther south would love to share the celestial view. But those auroras have been seen in the skies above Mexico, the event is very, very rare.
If you don't know what to expect, you might mistake the pale beams of aurora borealis for searchlights, perhaps from a new shopping center. But there are a few ways to tell which is which. As a rule, even the simplest aurora beams are tined with green and they appear to originate in the northern part of the sky.
They are most likely to occur in March and April and again in September and October. However, it is just possible that somebody to the north of you is playing with green tinted searchlights. In this case, you might have another clue, if you happen to know what's happening on the sun. For aurora lights are expected to follow a recent rash of sunspot activity.
This, we are told, is what causes them. Sunspots are huge magnetic storms on the face of the sun. These violent upheavals toss up masses of solar gases and their charged particles stream out into space. Some of them head toward the earth and strike our upper atmosphere. Charged particles of this sort are affected by magnetic fields. As they near the earth, they veer toward the magnetic poles, which are near the North and South geographic Poles.
This is why the aurora borealis tends to center around the North Pole and the aurora australis around the South Pole. The charged particles from the sun whiz across 93 million miles of space, silently and invisibly. But this changes when they strike the thin gases in our upper atmosphere. Here they collide with molecules of gas. This upsets their original charges and causes them to glow with auroral glimmers.
On a much smaller scale, something like this happens in a fluorescent light. The glass tube contains a skimpy helping of certain gases. When the electric current is turned on, it causes changes that make the gaseous atoms and molecules glow with fluorescent light.
The auroras do something like this on a scale big enough to span the skies. Their glimmering displays are thought to occur between 60 and 600 miles above our heads and they take many forms.
Often their pale greenish searchlights expand and curtain the sky with gauzy, waving draperies. Sometimes the display spans across the sky in a shimmering band of pale rainbow colors. The most dazzling display is said to be a fiery sunburst that pulses in the far northern sky. In any case, the celestial glory is centered toward our north magnetic pole and in the Southern Hemisphere, around the south magnetic pole.