Reading 2

Unit 2- Reading 2

Page 25

Time Zones

Many years ago, people used the sun to set their clocks. When people saw the sun exactly above them, they knew it was noon. Everyone living nearby had the same A sun time. But the sun was not exactly above in other locations to the east or west. As a result, people in different locations had different local times.

Different places, different times

As the earth turns each day, the sun appears to move across the sky. It appears to shift from east to west. As it moves, time varies. Sun time differs by about one minute every 13 miles (about 21 km) of distance on the earth. Imagine that the sun time is exactly 12:00 noon in one town. The sun-time is a minute earlier 15 miles to the west. This is because the sun is not yet exactly above. The sun-time is a minute later 13 miles to the east.

This is because the sun has already been exactly above. Towns 130 miles apart differ about 10 minutes in sun-times. Towns 1,300 miles apart differ about 100 minutes in sun-times.

For most of human history, differences in local sun times were not important. However, in the 19th century, railroads began to carry people over long distances. Travelers and railroad workers were confused by the many local sun-times. They set their watches to their own local time at the start of a trip. Later the train stopped at a distant town.

Then the watches were not accurate. They did not match the local time. Railroads needed to create an official time system to link the rail system together.

The time zone System

In 1884, a world committee met. They developed a world system that featured time zones. The committee divided the earth into 24 time zones. Each time zone was equal to one hour of time in a zone. When people traveled into a new time zone, they had to change their watches. People traveling east had to add one hour. Similarly, people traveling West had to shift the time back one hour.

The center of the first zone was in Greenwich, England. Exactly halfway around the earth an International Date Line was created. Here the time was exactly 12 hours different from Greenwich Time. Here the calendar date shifted. When it was Tuesday to the west of the line, it was Wednesday to the east of the line.

Today the time zone system is used by most countries of the world. It has helped world transportation and communication to develop.