We can only see light.

我们只能看见光

And light moves at a certain speed.

而光在以一定的速度运动

And so, as we look farther and farther away,

所以 我们看得越远

we're looking farther and farther back in time

看到的事物也就越古老

because we're seeing light coming to us from long ago.

因为我们看到的光是很久以前发出的

But there's only so far we can go back in time.

但是宇宙的历史是有限的

So there's only so far we can see.

所以我们能看见的范围也很有限

It's called the "Observable universe".

这称为 可观测宇宙

We can only map what's inside,

我们只能绘出在它范围内的物体

because the universe is only 13.7 billion years old.

因为宇宙只有137亿年的历史

There may well be a lot more universe outside,

在这范围之外可能还有更广阔的宇宙

but the light hasn't had time to reach us yet.

但是它们发出的光还未到达地球

In the last 20 years, we've seen this tremendous expansion,

过去的二十年间 我们掌握了许多知识

both in the amount and in the precision of knowledge

对可观测宇宙的了解

that we have about the observable universe.

实现了量的积累和质的飞跃

This has allowed cosmologists

这为宇宙学家

to make a map of unbelievable scale.

制作如此宏伟的星图奠定了基础

重点解释：

1.long ago 很久以前

例句：Amber is the resin of pine trees that grew very very long ago.

琥珀是古老的松脂。

2.so far 迄今为止

例句：It's the hottest day I've had so far.

这是迄今为止我经历的最热的一天。