Listen to part of lecture in an astronomy class.
Professor: Now astronomy didn't really bloom into the science it is today until the development of spectroscopy. Spectroscopy is basically the study of spectra and spectral lines of light, and specifically for us, the light from stars. lt makes it possible to analyze the light emitted from stars. When you analyze this light, you can figure out their distance from the earth, and identify what they are made of, determine their chemical composition.
Before we get into that though, it's probably a good thing to back up a bit. You all know how when you take a crystal prism and pass a beam of sunlight through it, you get a spectrum, which looks like a continuous band of rainbow colors.The light that we see with our human eyes as a band of rainbow color falls in a range of what's called visible light. And visible light spectroscopy is probably the most important kind of spectroscopy. Anyone want to take a stab at the scientific term for visible light? And I'm sure all of you know this because you all did the reading for today.
Student: Optical radiation. But l thought being exposed to radiation is dangerous.
Professor: Yes, and no. lf you are talking about radiation, like in the element Uranium, yeah, that's dangerous. But radiation as a general term actually refers to anything that spreads away from its source. So optical radiation is just visible light energy spreading out.
OK, so we've got a spectrum of a beam of sunlight and it looks like the colors bleed into each other. There are no interruptions, just a band flowing from violet to green, to yellow, to...you get the idea. Well, what happens if the sunlight's spectrum is magnified? Maybe you all didn't do the reading.Well, here's what you'd see. l want you to know this that this spectrum is interrupted by dark lines called spectral lines.
lf you really magnify the spectrum of the sunlight, you could identfy more than 100,000 of them. They may look like kind of randomly placed, but they actually form many distinct patterns. And if you were looking at the spectrum of some other star, the colors would be the same. But the spectral lines would break it up at different places, making different patterns. Each pattern stands for a distinct chemical element, and so different sets or patterns of spectral lines mean that the star has a different chemical composition.
Student: So how do we know which spectral patterns match up with which elements?
Professor: Well, a kind of spectroscopic library of elements was compiled using flame tests. A known element, say a piece of iron for example, is heated in a pure gas flame.The iron eventually heats to the point that it radiates light.This light is passed through a prism, which breaks it up into a spectrum. And a unique pattern, kind of like a chemical fingerprint of spectral lines for that element appears.
This process was repeated over and over again for many different elements, so we can figure out the chemical make up of another star by comparing the spectral pattern it has to the pattern of the elements in the library. Oh, an interesting story about how one of the elements was discovered through spectroscopy. There was a pretty extensive library of spectral line patterns of elements even by the 1860s.
A British astronomer was analyzing a spectrograph of sunlight, and he noticed a particular pattern of spectral lines that didn't match anything in the library. So he put two and two together, and decided there was an element in the sun that hadn 't been discovered here on the earth yet. Any guesses about what that element is? lt actually turned out to be prety common and l'm sure all of you know it. OK, let's try something else. Any of you happened to be familiar with the Greek word for "sun" by chance?
Student: Something like "Helius" or something like that. Oh it must be "Helium". So you are saying that Helium was discovered on the sun first.
Professor: Yes, and this is a good example of how important spectroscopy is in astronomy.
spectroscopy 光谱学 是对天文学有卓越的帮助的。在没有这个光谱学测定元素的方法之前，天文学未曾出现过bloom，知道spectroscopy发展了之后，才有了天文学的发展。这就像1+1>2的效应，可以理解为协同效应Synergy Effects，光学的发展促进了天文学对星球组成探索的一大跃进，就像之前通过放射性宇宙粒子的测定方法能够探知古墓穴的空间大小，为考古学提供了有效且高效的方法。
- bloom 繁荣
- spectroscopy 光谱学
- spectra 光谱(spectrum 的复数形式之一)
- emitted 散发(光、热、声音、气等)
- crystal 晶体
- prism 棱镜
- beam 光线；(粒子的)束
- stab 刺;尝试;企图
- Optical radiation 光辐射
- Uranium 铀
- spectral lines 光谱线
- Helium 氦
- impurities 杂质
- determine their chemical composition 确定它们的化学成分
- back up a bit 后退一点
- a beam of sunlight 一束阳光
- bleed into each other 互相渗透
- pretty extensive library 相当广泛的lib