【正文】 like. And ProtoIndoEuropean branched out into other languages, which evolved into others, so in the end, many languages spoken all over the world today can trace their ancestry back to one language, ProtoIndoEuropean, which was spoken several thousand years ago. Now, one way of representing the evolution of languages, showing the way languages are related to each other, is with the family tree model. Like a family tree that you might use to trace back through generations of ancestors, only it’s showing a family of geneticall related languages instead of people. A tree model for a language family starts with one language, which we call a mother language, for example, ProtoIndoEuropean. The mother language, is the line on the top of this diagram, over time, it branches off into new daughter languages, which branch into daughter languages of their own, and languages that have the same source, the same mother, are called sisters, they share a lot of characteristics, and this went on until we are looking at a big upside down tree languages like this. It is inplete of course, just to give you an idea. So that’s the family tree model, basically. Now, the tree model is a convenient way of representing the development of a language family and of showing how closely related two of more languages are. But it is obviously very simplified, having a whole language represented by just one branch on a tree doesn’t really do justice to all the variations within that language. You know, Spanish that spoken in Spain isn’t exactly the same as Spanish that is spoken in Mexico, for example. Another issue is that languages evolve very gradually, but the tree model makes it look like they evolve over night,like there was a distinct moment in time when a mother language clearly broke off into daughter languages. But it seems to me it probably wasn’t quite like that. 7 Lecture 2Astronomy(Radio Astronomy amp。 Optical Astronomy) Narrator Listen to part of a lecture in an astronomy class. Professor So how many of you have seen the Milky Way, the Milky Galaxy in the sky? You, you have? Student Yeah, I was camping, and there was no moon that night, it was super dark. Professor Anybody else? Not too many. Isn’t that strange that the Milky Way is the galaxy that the planet earth is in, and most of us have never seen it? Now, what’s the problem here? Student Light pollution, right? From street lights and stuff ... Professor Yes, Especially unshielded street light, you know, ones that aren’t pointed downward. Now, here’s an irony, the buiding we are in now, the astronomy building not far from our observatory, has unshielded lights. Student So the problem is pretty widespread. Professor It is basically beyond control, as far as expecting to view the night sky anywhere near city, I mean. I have lived around here my whole life. And I have never seen the Milky Way within city limits, and I probably never will. There is a price for progress, eh? But let’s think beyond light pullution, that’s only one kind of a technological advance that has interfered with astronomical research. Can anyone think of another? No? Ok, let’s look at it this way, we don’t only gain information by looking at the stars, for the past 70 years or so, we have also used radio astronomy1, which lets us study radio waves from the sky. Student How can you observe radio waves? I mean, tell anything about the stars from that. Professor Well, in optical astronomy, using a telescope and observing the stars that way, we rely on visible light waves. What we are seeing from earth is actually electromagnetic radiation that’s ing from stars. And just one part of it is visible light. But there are problems with that. When photons2 and light waves hit objects in our atmosphere, water droplets, oxygen and nitrogen molecules, dust particles and so on. These objects are illuminated, they are lit up, and those things are also being lit by all our street lights, by the moon, all these ambient light. And on top of that, when that visible radiation bounces off those molecules, it scatters in all directions. And well, light from stars, even nearby in our own galaxy, doesn’t stand a chance against that. Basically the light bouncing off all these objects close to earth is brighter than what’s ing from the stars. Now, radiowaves are electromagnetic radiation that we can’t see. Nearly all astronomical objects in space emit radio waves, whether nearby stars, objects in far away galaxies, they all give off radio waves. And unlike v