8.but it is interesting that Einstein's theory provided a basis for the idea of black holes before astronomers started to find some evidence for their existence. （第三段）
9.It is only recently that astronomers have begun specific research into black holes. （第三段）
10.And astronomers are planning a new observatory to study the individual exploding stars believed to be black holes. （第三段）
11.Binary stars， as their name suggests， are twin stars whose position in space affects each other. （第四段）
12.There might be a massive black hole at the center of our galaxy swallowing up stars at a very rapid rate. （第五段）
13.They show us a world which operates in a totally different way from our own and they question our most basic experience of space and time. （第五段）
Text B Worlds within Worlds
16.plateau （[复]plateaus或plateaux） n.高原
Phrases and Expressions
1.a great many 很多
2.above all 首先，首要
3.as a rule 通常；一般说来
together with 和
First of all let us consider the earth （that is to say， the world） as a planet revolving round the sun.The earth is one of nine planets which move in orbit round the sun.These nine planets， together with the sun， make up what is called our solar systems.How this wonderful system started and what kept it working with such wonderful accuracy is largely a mystery but astronomers tell us that it is only one of millions of similar systems in space， and one of the smallest.
The stars which we see glittering in the sky on a dark and cloudless night are almost certainly the suns of other solar systems more of less like our own， but they are so far away in space that it is unlikely that we shall ever get to know very much about them.About our own solar system， however， we are learning more every day.
Before the American and Russian astronauts made their thrilling journeys into outer space it was difficult for us to realize what our earth looked like from hundreds of thousands of miles away， but the photographs which the astronauts were able to take show us the earth in space looking not very different from what the moon looks like when we look at it from the earth.The earth is， however， very different from the moon， which the American astronauts have found to be without life or vegetation， whereas our earth is very much alive in every respect.The moon， by the way， is called a satellite because it goes round our earth as well as round the sun.In our words， it goes round the sun with our earth.