ASK A SCIENTIST
Question: Why do meteor showers happen?
On any clear night, if you look up at the sky, you should see at least one bright streak flashing between the stars. These flashes are actually happening in the earth's atmosphere and have been called "shooting stars" and "falling stars," but really are particles of meteoroid and comet dust falling into the atmosphere as the earth travels on its orbit. Some of these particles are interplanetary dust - material left over from the formation of the solar system, or created when larger objects collide.
When these particles move in the space between the planets, they are called meteoroids. As they fall through the earth's atmosphere, they are called meteors. If a piece remains after being heated in the atmosphere and lands on the surface of the earth, they are called meteorites. Few are large enough to land on the earth's surface and most evaporate in the atmosphere.
What about the comet dust? There are comets that pass through the solar system and come close to the earth's orbit. In the past, many of these comets have crossed the earth's orbit so that every year the earth passes close to where the comet had been. Comets leave behind particles of dust along their orbits. These particles continue to follow the comet's orbit. Upon entering the atmosphere, the particles cause the meteor flashes.
The majority of these meteors are smaller than a grain of sand and little, if any material actually lands on the earth. The streaks that you can see are made by some of the larger particles. It is estimated that eight billion of these meteors strike the earth daily but most of them are too small to make a visible streak.
The random meteor streaks that you can see at night are usually due to the interplanetary dust and particles from comets. Most meteor showers that are predictable and have names, like the Perseids (August 12) and the Leonids (November 17), are due to the earth passing through the comet dust as it crosses near a comet's orbit. The best time to observe them is after midnight.
What makes the flashes or streaks? These meteors enter the atmosphere at tens of thousands of miles per hour. The bumping into the atmosphere causes the meteors to heat up along with the surrounding air. This increases the energy of the molecules (like oxygen, nitrogen) in the air. When the air molecules lose this extra energy, they give it up as light. So along the path of the particle, you see a streak of light. The brighter the streak and the longer it lasts, the bigger the meteor.
Would you like to collect micrometeorites? Some meteors are made of nickel-iron and are large enough so that a small microscopic ball of material remains and lands on the earth. Look for directions on www.stanyssouthern.org, a web site for local science teachers. You may need the help of a parent and/or teacher to do this and a little patience. Good collecting!
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