Since the lifetime of a planet like ours is several billion years, we can expect that, if other civilisations do survive in our galaxy, their ages will range from zero to several billion years.(由于我们这样的行星的寿命是几十亿年，我们可以预测，如果我们星系中有其他生物生存，它们的年龄将从零到几十亿岁不等。)
According to previous speculation, these strands were gases that had been blown out by an explosion in the galaxy.(根据先前的推测，这些气体束是在一次星系的爆炸中炸出来的。)
The Galaxy consists of 100 billion stars.(银河系由1千亿颗恒星组成。)
Astronomers have discovered a distant galaxy.(天文学家们发现了一个遥远的星系。)
If many such chains were created in a differentially rotating galaxy, the distribution of stars would resemble the observed distribution in a spiral galaxy.(如果许多这样的链是在一个不同的旋转星系中产生的，那么恒星的分布将类似于在螺旋星系中观察到的分布。)
These stars vastly outnumber the other stars in a given galaxy.(在一个给定的星系中，这些恒星的数量远远超过其他恒星。)
Is this one galaxy or two?(这是一个星系还是两个？)
This line of reasoning underlies an exciting new theory of spiral-galaxy structure.(这一推理路线是一个令人兴奋的螺旋星系结构新理论的基础。)
From this you can calculate the total mass in the Galaxy.(据此，你可以计算出银河系的总质量。)
Observations indicate that gas clouds in galaxy M87 are whirling unusually fast about the galaxy's center.(观测表明M87星系的气体云围绕星系中心旋转的速度异常快。)
