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Meteors

 

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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

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