038慢速英语字幕(2)

慢速英语字幕,练习听力用得上

and bottom of the world.

In her book, Longitude, writer Dava Sobel tells the story about longitude and how the problem of knowing it was solved

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VOICE ONE:

For centuries, the great scientists of the world struggled to develop a way to learn longitude. To learn longitude at any place requires knowledge about time. A navigator needs to know what time it is on his ship and also the time at another place of known longitude - at the very same moment.

The Earth takes twenty-four hours to complete one full turn or (13) revolution of three-hundred-sixty degrees. One hour marks one twenty-fourth of a turn, or fifteen degrees. So each hour's time difference between the ship and the starting point marks a ship's progress of fifteen degrees of longitude to the east or west. Those fifteen degrees of longitude mark a distance traveled.

At the equator, where the Earth is widest, fifteen degrees (14) stretches about one-thousand-six-hundred kilometers. North or south of that line, however, the distance value of each degree (15) decreases. One degree of longitude equals four minutes of time all around the world. But in measuring distance, one degree (16) shrinks from about one-hundred-nine kilometers at the Equator to nothing at the north and south poles.

VOICE TWO:

For many centuries, navigators hoped they could find longitude by observing the movement of stars at night. During the day, the sun provided information about the time on a ship, and its direction. However, it did not provide necessary information about the time somewhere else. In the Sixteenth century, one astronomer suggested that navigators could observe the moon as it passed in front of different known stars to tell longitude. But, there was not enough information about the stars to use this method (17) effectively. Astronomers could not tell exactly where the moon would be from one night or day to the next.

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