英语听力文摘 English Digest 147、流星
时间：2019-02-16 作者：英语课 分类：英语听力文摘 English Digest
If you find yourself away from a city, spend an hour looking up on any clear, moonless night.
You're bound to see a few brilliant "shooting stars." These actually have nothing to do with stars: They're meteors, and if your viewing conditions are good, you can see about seven per hour on any given night.
During a "meteor shower" however, this rate may increase to over a hundred meteors an hour. What are meteors, and what makes them gather into showers?
Meteors are caused by bits of rocky material that enter our atmosphere from space, then burn up because of friction 1. They don't have to be big for you to see them. Surprisingly, most visible meteors are caused by debris 2 no larger than a single grain of sand. They burn so brightly because of tremendous friction when they hit our atmosphere at more than forty miles per second.
Why would something as random 3 as flying specks 4 of space debris gather into showers? It's because the Earth passes through the same regions of space each time it orbits the sun. Certain regions have more debris than others, so we have meteor showers on those nights.
Of course this raises the question of why certain parts of our orbit would be especially full of debris. The answer has to do with comets. Comets are big, dirty snowballs that orbit our sun. Long after a comet and it's tail have passed us by, it leaves behind a thin trail of dust and debris. If a comet crosses the Earth's orbit, we pass through this trail each year. For example, every October twenty-first we pass through the Orionid shower, which is debris left behind from Halley's comet.
- When Joan returned to work,the friction between them increased.琼回来工作后，他们之间的摩擦加剧了。
- Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体，并使其停止。
- After the bombing there was a lot of debris everywhere.轰炸之后到处瓦砾成堆。
- Bacteria sticks to food debris in the teeth,causing decay.细菌附着在牙缝中的食物残渣上，导致蛀牙。
- The list is arranged in a random order.名单排列不分先后。
- On random inspection the meat was found to be bad.经抽查，发现肉变质了。