概括：内容选自老托福听力，是练习托福听力的绝佳材料。


这次木有hints，大家压力大不大啊？
Most people think of astronomers as people who spend their time in cold observatories peering through telescopes every night. In fact, a typical astronomer spends most of his or her time analyzing data and may only be at the telescope about a few weeks of the year. Some astronomers work on purely theoretical problems and never use a telescope at all. You might not know how rarely images are viewed directly through telescopes. The most common way to observe the skies is to photograph them. The process is very simple. First, a photographic plate is coated with a light-sensitive material. The plate is positioned so that the image received by the telescope is recorded on it. Then the image can be developed, enlarged, and published so that many people can study it. Because most astronomical objects are very remote, the light we receive from them is rather feeble. But by using a telescope as a camera, long time exposures can be made. In this way, objects can be photographed that are 100 times too faint to be seen by just looking through a telescope.