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Meteors

 

Overview

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:
  • Quadrantids January 1-3
  • Perseids August 11
  • Orionids October 20
  • Geminids December 13

Activity

Make craters like David did in the Newton's Apple segment. Measure what factors make a difference in how big a crater is. Materials
  • a sandbox (the finer the sand, the better)
  • various objects: a marble, a large ball bearing, rocks of different sizes
  • a ruler
  • paper and pencil for recording data
  • a scale, such as a kitchen scale, for weighing the objects (optional)
  • a ladder (optional)
  1. Make a recording sheet with two columns--one for recording information about your "meteorite" and another for information about the craters it produces.
  2. Prepare a smooth, flat surface in the sandbox at least 30 cm (1') on a side. Be sure the sand is loose and dry beneath it.
  3. Pick an object to act as your meteorite. Measure and record its length and, if you have a scale, weigh your meteorite and record that figure, too.
  4. Make sure no one is in the way!
  5. Throw the meteor down into the middle of the sand as hard and as fast as you can.
  6. Look at the crater you made. Measure its diameter (to the nearest millimeter, if you can) and its depth.
  7. Repeat steps 4 through 6 at least two more times to get three or more measurements from your meteorite.
  8. Repeat steps 3 through 7 using different objects as meteorites.
  9. (Optional) Repeat the steps, substituting flour for sand and dropping the objects instead of throwing them. This will remove the added variable of velocity. Observe how your results differ when you drop the object into flour instead of throwing it into sand. Questions
    1. What problems did you encounter as you tried to measure the craters? How did you deal with those problems?
    2. How did your craters vary? Did the same meteor always produce a crater of the same size? How did changing the meteor change the crater you made? Did you see any patterns?
    3. How could you change this investigation? Can you think of other materials that would make good craters? Can you think of other things you might measure?
    4. How does making craters in a sandbox helps us understand real meteorite craters?
    5. Based on the final pattern, can you tell which craters were made first? How can astronomers estimate the age of meteor craters on other planets?

Resources

  • Begley, S. (1992, Nov 23) The Science of Doom. Newsweek, pp. 56-60.
  • Berger, M. (1981) Comets, meteors, and asteroids. New York: G. P. Putnam's Sons.
  • Darling, D. J. (1984) Comets, meteors, and asteroids: Rocks in space. New York: Dillon.
  • Fichter, G. S. (1982) Comets and meteors. New York: Franklin Watts.
  • Hecht, J. (1993, Jan 16) Stony asteroid devastated Siberia. New Scientist, p. 16.
  • Langreth, R. (1992, Sept) Asteroid Watchers. Popular Science, pp. 76-81.