英语听力：自然百科 穿越银河系的旅行 Through Milky Way—21

 Imagine the disc of our galaxy¹, if you just took a disc of stars and put it there, gravity would tend to make this disc collapse/ into itself and it would immediately just fall together. That is not what we see with the galaxy.

 

 

 

What’s actually going on is the stars are orbiting around the center and that is what keeps them from falling in, in much the same way that the Earth is orbiting around the Sun. 

 

 

 

The planets in our solar system are in a delicate balance between gravity pulling them towards the Sun and their orbital velocity² wanting to pull them outwards³ into space. 

 

 

 

To keep in balance, planets / further from the Sun must orbit more slowly. If you go to / more distant planets at the edge of the solar system, they are going around the Sun much more slowly than the Earth is, and that’s because / the gravity is weaker. The same holds true for stars in the Milky⁴ Way. All of them are orbiting / the center of the galaxy. But the stars in the outer arm should be travelling more slowly then those closer to the galaxy’s heart. 

 

 

 

What’s interesting, that is not what’s going on. The stars in the outer parts of the galaxy are spinning around just as quickly as those in the inner parts. And they are not the only ones, it’s not just our galaxy, it is every galaxy we look at. Every galaxy we look at seems to be spinning too fast in its outer part. These speeding stars should be flying out of the galaxy altogether. But they are not. That is a puzzle. This means that there is a lot more mass there that we just can’t see. 

 

 

 

It’s this mass that must produce the gravity that hold these stars in their orbits. But when astronomers⁵ look for the mass, there appears to be nothing there. It’s led cosmologists like John Premark to an astounding⁶ conclusion.

1 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

2 velocity   

n.速度，速率

参考例句：

• Einstein's theory links energy with mass and velocity of light.爱因斯坦的理论把能量同质量和光速联系起来。
• The velocity of light is about 300000 kilometres per second.光速约为每秒300000公里。

3 outwards   

adj.外面的，公开的，向外的；adv.向外；n.外形

参考例句：

• Does this door open inwards or outwards?这门朝里开还是朝外开？
• In lapping up a fur,they always put the inner side outwards.卷毛皮时，他们总是让内层朝外。

4 milky   

adj.牛奶的，多奶的；乳白色的

参考例句：

• Alexander always has milky coffee at lunchtime.亚历山大总是在午餐时喝掺奶的咖啡。
• I like a hot milky drink at bedtime.我喜欢睡前喝杯热奶饮料。

5 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

6 astounding   

adj.使人震惊的vt.使震惊，使大吃一惊astound的现在分词)

参考例句：

• There was an astounding 20% increase in sales. 销售量惊人地增加了20%。
• The Chairman's remarks were so astounding that the audience listened to him with bated breath. 主席说的话令人吃惊，所以听众都屏息听他说。 来自《简明英汉词典》