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Light travels at a speed which is about a million times faster than the speed of sound. In a second, light travels about 300,000km, but sound travels only 340m. You can get some ideas of this difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke come from his gun before the sound reaches your ears.
This great speed of light produces some strange facts. Sunlight takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light rays left the moon 1.3 seconds before they reach you. The nearest star is so far away that the light which you can see from it tonight started to travel towards you four years ago at a speed of nearly 20 million km, per minute. In some cases, the light from one of tonight's stars started on its journey to you before you were born.
Thus, if we want to be honest, we can not say,
“the stars are shining tonight.”We have to say,“The stars look pretty. They were shining four years ago but their light has only just reached the earth.”阅读短文，选择最佳答案．
(1) The speed of light is ________ than the speed of sound.
[ ]
A
．a million times slowerB
．about millions of times fasterC
．about a million times faster(2) If you stand 200 meters away from a man who is firing a gun to start a race, you will find out that ________.
[ ]
A
．you can hear the gun before you see the smokeB
．sound doesn't travel as fast as lightC
．the sound of gun will reach you before the man fires his gun(3) Sunlight ________ to the earth than the light of the moon.
[ ]
A
．has to travel a greater distanceB
．moves less quicklyC
．is less powerful(4) The scientific way of saying
“the star are shining tonight”should be ________.[ ]
A
．the stars have been shining all the timeB
．the stars seen tonight will be shining four years laterC
．the stars were shining long ago but are seen tonight(5) The light of the nearest star you see tonight has been ________ for four years.
[ ]
|
A ．away from the star |
B ．on the moon |
C ．away from the sun |
The sun is a star. In the sky there are thousands of stars like the sun. They are as large as the sun and as
hot as the sun. At night you can see many stars, but in the daytime you can see only one star, the sun.
The sun is much nearer to us than any other star. That is why it looks the biggest and the brightest of all
the stars. The distance of the sun from the earth is as much as 150 million kilometers. Most of the stars are
thousands of light years away from the earth.
Do you know the light year? Nothing in the world travels faster than the light. It travels 300,000 kilometres
a second (one-sixtieth of a minute). And one light year is the distance that light travels in one year.
B. people can not live on the earth
C. only some plants can live on the earth
D. there will be no stars in the sky
B. there are no other stars in the sky
C. the sun is the biggest in the sky
D. the other stars only come out at night
B. The sun is the nearest star to the earth.
C. The sun is 150 kilometres away from the earth.
D. The sun is much bigger and brighter than other stars.
B. 300,000 metres a second
C. 300,000,000 metres a second
D. 3000,000 kilometres a minute
B. year
C. a far-away place
D. a very, very long way
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