Where Do Shooting Stars Come From?
“OOH, LOOK! There goes another one!” “Where? Where?” Have you ever uttered such words as you searched the night sky for shooting stars? Perhaps the first time you saw one suddenly tracing a luminous line across the star field above you, it looked as if one of the stars had suddenly gone shooting across the sky. Of course, shooting stars are really misnamed. They may “shoot,” but they are a far cry from being stars.
Astronomers call them meteors. And whereas an average star could swallow up our whole planet a million times over, it is our planet that swallows up these meteors by the millions. What are meteors, and where do they come from?
Well, they have a lot to do with comets. Halley’s comet, a famous example, swept by the earth in 1986 on its 76-year-long elliptical journey around the sun. Because comets apparently consist mostly of ice and dust, they are sometimes called dirty snowballs. When a comet approaches the sun, its surface warms up, releasing dust and gas. The radiation pressure of sunlight pushes the solid material back in a glowing tail of dust. The comet thus leaves in its wake a dusty trail of debris—particles that while still in space, are called meteoroids. Most cometary dust is too small to become visible meteors. A small fraction are about the size of a grain of sand, while a few are as large as small pebbles.
In a few cases, a comet’s orbital path intersects that of the earth. That means that the earth meets the same trail of dust each time it plows through the comet’s orbit. When this happens the tiny meteoroids plummet into the atmosphere at high speeds—up to 44 miles per second [71 km/sec]. As they fall, the larger ones heat up and burn, making the white-hot streaks across the sky that are known as meteors.
When the earth crosses a comet’s path, the meteors appear to shoot out in all directions from the same point in the sky, which is called the radiant. From these radiants, meteor showers fall at regular times of the year. One popular display is the Perseids shower, so named because its radiant is found in the Perseus constellation. When the Perseids reaches its peak about August 12 or 13 every year, it is a dazzling show. Over 60 meteors may fall every hour.
About October 21 you may see the Orionids shower, which, like the earlier Aquarids shower, is said to be caused by meteoroids from Halley’s Comet. According to the journal Astronomy, scientists estimate that Halley’s comet “can make 100,000 orbits before losing all of its material.” If their hypothesis is correct, Halley’s comet will make regular visits during the next 7,600,000 years! And even after it is long gone, no doubt its trail of dust will continue to provide the earth’s inhabitants with shooting stars for ages thereafter. Many of the meteors we currently see apparently come from comets that have long been defunct.
Scientists figure that worldwide, there are some 200 million visible meteors in our atmosphere every day. And as for the more spectacular meteor showers, well, there is always next year—and millions more to come!