【導讀】Ihope. I’llcertainlytry.read.Ok…Oh…Aha…Um…thepre-operationalstage?wouldbedeveloped.Enhums…Butwhatifshedoesn’t?Imean,whatifshedoesn’tdemonstratethose. behaviors?What’sthat?

　　

【正文】 ubadours than we do about the Chanson authors, because they often had small biographical sketches added to their poems that gives more specific information about their social status, geographical location and small outlines of their career. These information wasn’t particularly reliable because they were sometimes based on fictitious stories, great adventure or the scrape together from parts of the different poems. But there is enough to squeeze or infer some facts about their social class. The political climates have settle down enough so that troubadours had the luxury being able to spend most if not all of their time, creating, crafting or posing their love songs for their audiences. And yes these poems were also songs。 many troubadours were able to make a living being full time poets which should tell you something about the value of that profession during the medieval times. TPO 13 – Lecture 4 Narrator: Listen to part of a lecture in an astronomy class. Professor: OK, I wanna go over the different types of meteoroids, and what we39。ve learned from them about the formation of earth, and solar system. Uh… the thing is what39。s especially interesting about meteoroids is that they e from interplaary space, but they consist of the same chemical elements that are in matter originated on earth, just in different proportions. But that makes it easier to identify something as a meteoroid, as it opposed to…to just a terrestrial rock. So to talk about where meteoroids e from, we need to talk about ets and asteroids, which basically...they’re basically made up of debris left over from the origin of the solar system billion years ago. Now I39。m going a bit out of a boarder here…umm…I39。m not going to go into any depth on the ets and asteroids now, but we39。ll e back later and do that. From now, I39。ll just cover some basic info about them. OK, ets and asteroids. It might help if you think of...remember we talked about the two classes of plas in our solar system? And how they differ in position? The terrestrial plaslike Mars and Earthposed largely of rocks and metals, and the large gas giants, like Jupiter. Well, the solar system also has two analogous classes of objects, smaller than plasnamely, asteroids and ets. Relatively near the sun and inner solar system, between Jupiter and Mars to be precise, we’ve got the asteroid belt, which contains about 90 percents of all asteroids orbiting the sun. These asteroids are…uh…like the terrestrial plas, and they39。re posed mostly of rocky materials and metals. Far from the sun, in the outer solar system, beyond Jupiter39。s orbit, temperatures are low enough to permit ices to form out of water and…and out of gases like methane and carbon dioxide. Loose collections of these ices and small rocky particles form into ets. So ets are similar in position to the gas giants. Both ets and asteroids are...typically are smaller than plas. And even smaller type of interplaary debris is the meteoroid. And it39。s from meteoroids that we get meteors and meteorites. Roids are, for the most part anyway, they are just smaller bits of asteroids and ets. When these bits enter earth’s atmosphere, well, that makes them so special that they get a special name. They39。re called meteors. Most of them are very small, and they burn up soon after entering earth’s atmosphere. The larger ones that make it through the atmosphere and hit the ground are called meteorites. So meteorites are the ones that actually make it through. Now we39。ve been finding meteorites on earth for thousands of years, and we39。ve analyzed enough of them to learn a lot about their position, most e from asteroids, though a few may have e from ets. So essentially they are rocks, and like rocks, they39。re mixtures of minerals. They are generally classified into three broad categoriesstones, stony irons and irons. Stone meteoroids, which we refer to simply as, uh, stones, are almost entirely rock material. They actually account for almost all of the meteorite material that falls to earth. But even so, it39。s rare to ever find one. I mean, it39。s easier to find an iron meteorite or stony iron. Anyone guess why? Look at their names. What do you think iron meteorites consist of? Student: Mostly iron? Professor: Yeah… iron and some nickel, both of which are metals . And, if you39。re trying to find metal? Student: Oh! Metal detectors! Professor: Right, thank you. At least that39。s part of it. Stone meteoroids, if they lie around exposed to the weather for a few years, well, they39。re made of rock, so they end up looking almost indistinguishable from mon terrestrial rocksonce that originated on earth. So it39。s hard to spot them by eye. But we can use metal detectors to help us find the others, and they39。re easier to spot by eye. So most of the meteorites in collections, uh, in museums, they39。ll be...they39。re iron meteorites, or the stony iron kind, even though they only make up about 5 percents of the meteorite material on the ground.