Dianne Cravey, age 12, of Ashburn, Ga., for her question:
What causes a shower of meteors?
If your eyes are alert, you can spot an average of ten meteors in an hour. These so called shooting stars may dart across any part of the night sky. But on certain nights, if you know where to look, you can spot a shower of meteors with dozens of shooting stars.
If the sky is clear, you may spot a shower of meteors this very night. The fiery sparks will seem to shoot from near the constellation Orion, the Heavenly Hunter. They seem to fan out from a central point which astronomers call the radiant of a meteor swarm. Actually, they are traveling side by side in parallel lines. Like a railroad track, they merely seem to taper towards a distant vanishing point.
Tonight's meteor swarm is called the Orionids, because it seems to originate near Orion. Of course, it is no part of these faraway brilliant stars. It is part of the solar system where it was born. Like most meteor swarms, it is debris left by a passing comet. The Orionids were left by the glamorous visitor called Halley's comet.
Meteor swarms occur when teeming fragments of dusty debris collide with the earth and burn up in the atmosphere. They may be pulled from the head of a comet by the sun or by gravity of the earth. The teeming fragments of meteoric material stretch along the comet's orbit. If they cross the earth's orbit, we see them as a shower of shooting stars. This occurs when the earth passes through the point where the meteors crowd around its path.
From October 18 to 23, the earth is orbiting through the Orionids ieft by Halley's comet. between May 4 and 6, on the opposite side of its orbit, the earth passes through another meteor swarm left by Halley's comet. They axe the Aquarids which seem to come from the constellation Aquarius, the Water Carrier.
A bright meteor swarm may appear unannounced. But most of them occur on schedule and we know more or less when and where to expect them. They are named from the constellation from which they seem to arrive.
The biggest swarm of meteors is the Perseids, streaming from Perseus in the Northwestern sky. This shower of sparks reaches its peak near August 11, though it may be seen for several weeks. The Perseids have appeared since 1862, Where a big comet crossed our orbit as it swooped around the sun.