What are meteors and where do they come from?
What is a meteor? When are you most likely to see meteors? Is there any way to predict them?
David wants to learn more about meteors after a large one crashes through his roof!
Most of us see meteors by chance. You're out with a friend on a dark night, and suddenly you see a bright object streak across the sky. You shout, "Look at the shooting star," but by the time your friend looks, it's gone. If you're lucky, you see it together.
But can you try to see a meteor? You bet. Simply go out at night and watch and wait. Lie on your back, and look up at the sky. If you don't get too cold and you don't fall asleep, you'll probably see about five meteors an hour, though you can't predict exactly where or when they'll appear. These sporadic meteors are just chance collisions between a bit of space dirt and Earth's atmosphere.
A typical meteor has a mass that is only a fraction of a gram. When it hits the atmosphere, it is probably going 10-40 kilometers per second (20,000-90,000 miles per hour). When it enters Earth's atmosphere, its surface heats up because of friction. Bits of matter fall away, and atoms evaporate from the surface to form a hot, gaseous envelope around the tiny particle. This hot envelope, which may be a foot or more in diameter, hurtles through the atmosphere, making a streak of light in the sky. The meteor usually burns up in the atmosphere--and the envelope dissipates--by the time it's within 60 kilometers (200,000 feet) off the ground.
If you're really lucky, you'll see a much larger meteor. The bigger the piece of dirt, the longer and brighter the streak in the sky. Fewer than one in a thousand visible meteors are fireballs or bolides, which are especially bright and can make explosive or hissing noises.
If the meteor slows down enough, it will stop evaporating before it has been completely obliterated. These meteorites actually will fall to the ground.
If you don't like waiting around for a chance encounter with a sporadic meteor, you should go out on a night when astronomers are expecting a meteor shower. Several times a year, Earth passes through a known cloud of space dirt, usually debris from a comet. In these clouds, the meteoroids--the bits of matter in space--are about 50 kilometers (30 miles) apart.
Because meteor showers occur as Earth moves through a particular region of space, they happen at the same time every year. Here are a few of the most reliable meteor shower dates:
Additional sources of information
Find out what the size of a crater can tell us about the meteorite that made it.
Make craters like David did in the Newton's Apple segment. Measure what factors make a difference in how big a crater is.
Go out with a friend to a dark place at night--during a meteor shower if you can--and try to see some meteors. Bring a flashlight so you can find your way safely. While you watch, see if you can identify the path the meteors take.
Get a topographic map of Meteor Crater, Arizona. How do they indicate the depression on the map? Find where Meteor Crater is on a map of the United States. Using the topographic map, make a model of Meteor Crater with clay or plaster of paris.
Thousands of meteorites fall on our planet each year. They are small and usually harmless. Read "The Science of Doom" in Newsweek (Nov 23, 1992) to learn about the probability of a much larger meteorite making contact with Earth. When was our last "big hit"? Stage a debate regarding the use of tactics to divert an approaching meteor.
Find out about meteorite craters on other planets. Get photographs of the surfaces of the moon, Mars, and Mercury. How are they similar? How can you tell them apart? How can astronomers tell the age of meteor craters just from looking at their pictures?
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Educational materials developed with the National Science Teachers Association.