But two hundred years ago it didn't seem so unlikely.  但是两百年前还颇言之成理

It was widely believed that  当时一般人认为

the Earth was only a few thousand years old.  地球只有几千年的历史

But in the mid-nineteenth century a new science  但是19世纪中期

was emerging that was painting  一股新的科学势力兴起

a very different picture of the age of the Earth.  并对地球的年龄提出截然不同的见解

By looking at the deepest layers of rocks geologists  地质学家研究深层岩石后

were discovering that the Earth was much older  发现地球年龄远超出

than anyone had previously imagined.  一般人的预期

If that was true then the sun also had to  如果此言属实

have been burning for much,much longer.  那么太阳燃烧的时间也应该久得多

You can see the strata and the lines in the rock in back of you  后方岩石的地层和线条

that represent hundreds of  代表了

millions of years of geological history.  好几亿年的地质历史

The top of Sacramento Peak up beyond this,  我们在更后面的沙加缅度峰上

we find fossils that are 300 million years old.  找到了有三亿年历史的化石

Below Sacramento Peak you've got more than a kilometre  沙加缅度峰下方，有一公里多的地层

of these strata that are far older than that.  年代比三亿年还久远

From the age of these strata geologists knew  地质学家藉由这些地层得知

that the earth was at least a billion years old.  地球的历史至少有十亿年

At the same time astronomers thought  但天文学家却认为

the sun was only 10, 000 years old.  太阳只有一万年的历史

If the geologists were right then astronomers  如果地质学家说得对，那么天文学家

had to find some other source for the Sun producing its energy.  必须另外想办法解释太阳能量的来源

The search for the source of energy  寻找支持了太阳

that could power the sun for billions of years  数十亿年的能量来源

lasted for nearly a century.  持续了将近一个世纪

Eventually scientists would find the answer in the forces  最后科学家终于在凝聚原子的力量

that hold atoms together and in the nature of matter itself.  和物质的本质中找到答案

But first you have to know what the sun is made of.  但首先我们必须先搞清楚太阳的组成

To find that out you need to take a very close look at sunlight.  想要得到答案，必须仔细观察阳光

When you take the light from the Sun and pass it through a prism,  若让阳光穿过棱镜

spread it out into the colours,  让阳光分色排列

as you look through it you notice that it isn't uniform,  你会发现阳光的组成并不一致

that there are places that are darker.  有些地方比较暗

Each of those dark lines is due to a specific chemical element.  这些暗沉的线条都代表着特定的化学元素

Each element has its own series of lines that are specific to it.  每一种元素都拥有一系列专属的线条

Each chemical element absorbs light at specific frequencies  每种化学元素都会吸收特定频率的光线

removing a strip from the spectrum.  进而移除光谱上的特定区块

As the light passes through the sun,  光线穿过太阳时

all the elements leave their mark.  所有的元素都会留下它们的印记

So when the light arrives at the Earth it contains  所以抵达地球的光线

the complete chemical formula of the sun.  包含了太阳的完整化学式

If we take the spectrum and spread it out to fine details  若是把光谱摊开…

and what we've done here is stacked up  我们在这里

pieces of the spectrum one on top of each other  把几块光谱上下堆叠

you see all of these dark areas.  你们可以看到这些暗色区域

The key to figuring out how much of these elements  至于判定元素含量的关键

are there is the breadth and the depth of the line;  则是这些线条的宽度和深度

how dark is the line and how broad is it.  也就是它们的深浅和宽窄