天文學這門自然科學的課程，相對來說是非常具有學科特色的，不像某些人文科學類的內容在日常生活或者平時積累中可以獲取一些背景知識，天文學不是刻意了解的話肯定是不知道的。所以，相較而言，了解天文學的常考背景就變得非常重要了。本文從TPO真題中節選了一些天文學的考查范圍以及學科知識來談談托福聽力中天文學出現的4大范圍。
天文學常考學科范圍一：各種星系相關
TPO14 Lecture3考到的內容是：在整個太陽系中，行星根據組成成分不同分成兩類：The terrestrial planets(類地行星)--like Mars and Earth(火星和地球)--composed largely of rocks and metals(由大多數的巖石以及金屬組成), and the large gas giants(類木行星), like Jupiter(木星). Well, the solar system also has two analogous classes of objects, smaller than planets--namely, asteroids and comets(彗星和小行星是行星的類似物，只是相對來說體積較小).
Both comets and asteroids are...typically are smaller than planets(彗星和小行星體要比行星來的小). And even smaller type of interplanetary debris is the meteoroid. And it's from meteoroids that we get meteors and meteorites(流星體是一種更小的東西，流星和隕石也是由此得來的). When these bits enter earth’s atmosphere, well, that makes them so special that they get a special name. They're called meteors(進入大氣層的稱之為流星). 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(經歷燃燒等掉入大地的叫做隕石).
天文學常考學科范圍二：外太空各種星系是否有生命存在
首先，從科學角度出發，只有一些類地行星(terrestrial planet)上才可能適宜生命存在，一般常考的是火星上是否有生命跡象存在。以TPO30 Lecture3為例，文中提到因為近來的一些發現，尤其是一些微生物的發現，使得人們非常好奇火星上是否有生命存在。文中考到的內容Jarosite(黃鉀鐵礬) is a yellowish brown mineral with a crystalline structure(晶狀體結構) that’s also found on Earth. It contains iron, potassium and hydroxide(含鐵，鉀，氫氧化物). The interesting thing is that on Earth at least it needs highly acidic water to form(需要強酸性的水). So we’ve got water or had it at one point(所以能證明水的存在)……But Jarosite on Earth incorporates all kinds of microorganisms into its crystalline structure. So it’s possible that if the Jarosite on Mars was also formed with the help of microorganisms(還有可能微生物也起到了一定的作用). 天文學常考學科范圍三：光譜技術
TPO5 Lecture3中就考到了Spectroscopy is the study of the interaction between matter and light(光譜研究物質和光之間的關系，大多時候的光譜都是一些星星發出的光). Now, visible light consists of different colors or wavelengths, which together make up what's called spectrum, a band of colors, like you see in a rainbow. And all substances, all forms of matter, can be distinguished according to what wavelength of light they absorb and which ones they reflect. It's like, um, well, every element has, what we call, its own spectral signature(不同的顏色代表不同的化學組成成分). If we can read that signature, we can identify the element. And that's exactly what spectroscopy does(而這個技術通常用于藝術發展史中的藝術品修復技術).
天文學常考學科范圍四：天文學實際應用
Polynesians was to look for a star pair, that’s two stars that rise at the same time, or set at the same time, and navigators could use these pairs of stars as reference points, because they rise or set together only at specific latitudes(一對星星在某個相同的緯度同起同落). So navigators might see one star pair setting together. And, uh…would know how far north or south of the equator they were. And if they kept on going, and the next night they saw the pairs of stars setting separately, then they would know that they were at a different degree of latitude(航海家通過辨別星星的緯度來辨別位置航海方向), so looking at rising and setting star pairs is a good technique.
