What is the sky？ Where is it？ How high is it？ What lies above the sky？ I am sure that you have asked questions like these. They are very difficult to answer， aren’t they？
Perhaps we can answer some of these questions now. What is the sky？ It is vast space. Where is the sky？ It is all around the world. In the sky there is the sun， the moon， and all the stars.
Scientists have always wanted to know more about space. They use telescopes to obtain information. But this is not enough. So they want to send men to some of the other worlds in space.
The moon is the nearest heavenly① body to the earth. An airplane cannot fly to the moon， because the air only reaches a height of 240 kilometers. Then there is no air. But a rocket can fly even when there is no air.
A rocket is made of metal. There is a hot gas inside it. The hot gas rushes② out of the end of the rocket to push up the rocket into the air.
Rockets can fly far out the earth into space. Rockets have already taken men to the moon. They may be able to③ go anywhere in space one day.
① heavenlyadj. 天体的
② rushv. 冲，跑
③ be able to能，会，可以
空中火箭
天空是什么？它在哪儿？有多高？上方有着什么？我确信你问过类似这样的问题。这些问题是很难回答的，是吧？
或许现在我们能够回答这些问题中的一些。天空是什么？是广阔的空间。天空在哪里？遍及全球。天空中有太阳、月亮群星。
科学家总是想更多地了解太空。他们用望远镜获取信息，但这是不够的。因此他们要把人送到太空中的其他星球上去。
月球是离地球最近的天体。飞机不能飞达月球，因为飞机只能飞到24万米的高度，再往上就没有空气了。但是火箭可以，就算无空气时也能飞行。
火箭由金属制成，里面有一种热的气体，气体从火箭末端冲出来时，火箭被推向空中。
火箭能够飞出地球进入太空并且火箭已经载人到过了月球。总有一天，它们也许能够进入太空的任何地方。