What do astronomers now realize are not rare occurrences？

What do astronomers use photographic plate for？

A．Decreasing the time it takes to photograph objects.

B．Avoiding using a telescope.

C．Sharpening the color of what they observe.

D．Obtaining images of distant objects.

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

A．They spend most of their time looking through telescopes.

B．They are constantly analyzing data.

C．They often live near observatories.

D．They devote a lot of time to theoretical problems.

Why do astronomers often use photographic plates？

A．To decrease the time it takes to photograph objects.

B．To avoid using a telescope.

C．To sharpen the color of what they observe.

D．To obtain images of distant objects.

ries 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. The most common way to observe the skies is to photograph them.

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

A．They spend most of their time looking through telescopes.

B．They are constantly analyzing data.

C．They often live near observatories.

D．They devote a lot of time to theoretical problems.

听力原文： 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 view 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 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 that are hundreds of times too faint to be seen by just looking through a telescope can be photographed.

According to the speaker what do people often think about astronomers

A．They spend most of their time looking through telescopes.

B．They are constantly analyzing data.

C．They often live near observatories.

D．They devote a lot of time to theoretical problems.

ories 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 for 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 a hundred times too faint to be seen by just looking through a telescope.

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

A．They spend most of their time looking through telescopes.

B．They are constantly analyzing data.

C．They often live near observatories.

D．They devote a lot of time to theoretical problems.

Why do astronomers make long time exposures？

A．To spend less time at their telescopes.

B．To overcome the problem of weak light.

C．To take more photographs.

D．To photograph astronomical objects without using a telescope.

d on lunar months. When people started fanning, the sages of the tribes became very important. They studied the sky and gathered enough information to be able to predict when the seasons would change, and were able to announce when it was time to plant crops.

The divisions of time we use today were developed in ancient Babylonia 4,000 years ago. Babylonian astronomers believed the sun moved around the Earth every 365 days. They divided the trip into 12 equal parts, each with 30 days. Then they divided each day into 24 equal parts or hours, and divided each hour into 60 minutes, each minute into 60 seconds.

Humans have used many devices to measure time. he sundial was one of the earliest and simplest. However, the sundial worked well 0nly when the weather was fine, so other ways of measuring the passing of time were invented. One device was the hourglass. By the eighteenth century, people had developed mechanical clocks and watches. So we have devices to mark the passing of time, but what time is it now？ Clocks in different parts of the world do not show the same time at the same time, because time on Earth is set by the sun's position in the sky above us. As international communications and travel grew, it became clear that a way to establish a common time for 'all parts of the world was needed. In 1884, an international conference divided the world into 24 time zones, each zone represents 0ne hour. The astronomical observatory in Greenwich, England, was chosen as the starting point for the time zones. Twelve zones are west of Greenwich. Twelve arc east. The time at Greenwich measured by the sun is considered by astronomers to be Universal Time, also known as Greenwich Mean Time.

What does the passage mainly discuss？

A．Why we measure time the way we do.

B．Ways of measuring time.

C．The development of universal time.

D．How time is measured.