According to the passage, what do people often think about astronomers?

(17)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/her time analyzing data and may only be at the telescope 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.(18 - 1)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.(19)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 people can study it.(18 -2)Because most astronomical objects are very remote, the light we receive from them is rather feeble.(18 - 3)(20)But by using a telescope as a camera, long time exposures can be made. In this way objects that are hundreds of times too faint to be seen by just looking through a telescope can be photographed.