What is the sky？ Where is it？ How bright is it？ What lies above it？ These questions are difficult to answer, aren’t they？

　　Is the sky blue？ The sky has no color. We know that there is air around the world. When planes fly, they need air to lift their wings. Planes can’t fly very high because the air gets thinner when they go up higher. If we go up about 1,200 kilometers from the earth, we’ll find no air there.

　　When we talk about the sky, we usually mean the atmosphere around the earth. It is like a very thick “cover” over the earth and keeps it warm. Without the “cover”, the earth would be a very cold place and nothing could live on it.

　　Looking up above us, you will see the blue sky with white clouds. It is usually light blue, but the sky would be dark blue if you go to the top of the highest mountains. And you will see fewer clouds between you and the sun.

　　And if you sit in a spaceship high above the earth, there is no air at all. The sky would be so dark that its color would be black.

　　Sometimes the sky doesn’t look blue. When the sun rises and falls, you will see red, orange, and other colors in the sky. These are the most beautiful moments of the day.

　　Now you may understand that we see colors because the air scatters (散射) the sunlight. Light travels through the air. Without air, there would be no light and no colors.

1.Planes can’t fly very high because ____________.

A．there is air around the world

B．the air gets thinner when they go up higher

C．it’s warmer in the sky

D．the air gets thicker when they go up higher

2.We can see colors of the sky because ____________.

A．the sun rises and falls every day

B．the sky has lots of colors

C．the air scatters the sunlight

D．the sunlight has many colors

3.Which of the following is TRUE？

A．There is little air without light and colors in the sky.

B．The sky will look red, orange and other colors at noon.

C．The sky has only one color when the sun rises and falls.

D．The sky is dark blue if you go to the top of the highest mountains.

The sun, the moon and the stars(星星)are all in the sky． We see the moon and the stars at night． The sun is a ball． It’s much bigger than the moon． It gives us heat(热量)．The sun has a family． It’s the biggest member of the family． The moon is a ball, too, like the sun and the earth． Sometimes it looks as round as a plate(盘子)．Sometimes it looks half a plate． It looks bigger because it’s much nearer to the earth． It’s much smaller than the sun． It’s smaller than the stars． The light on the moon comes from the sun． It has no light of its own．
The stars look smaller than the sun． They look small because they are very far away from us． All day the stars are in the sky． But the light from the sun is too bright． We can’t see the stars in the day．
【小题1】The sun, the moon and the stars are in the sky．
【小题2】 The moon is bigger than the stars．
【小题3】 The moon has its own light(光)．
【小题4】 The sun, the moon and the stars give us light and heat．
【小题5】The earth is one of the planets(行星)．