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What Are Time Zones?

Vocabulary
 challenging words: ante-meridian, contiguous, post-meridian, zone, based, continental, midday, rotation, nighttime, position, directly, alaska, gain, time, lines, divide content words: North Pole, South Pole, International Date Line, Date Line, New York City, United States, North America, South America

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 What Are Time Zones? By Cindy Grigg

1     Time zones are based on the position of the sun. We say that 12 o'clock noon is midday. Then the sun is at its highest point, directly overhead. The Earth spins or rotates on its axis, like the spinning of a top. As the Earth spins, the sun looks like it moves across the sky from east to west.

2     It takes the Earth about 24 hours to make one rotation. This causes day and night. When one side of the Earth is turned toward the sun, it is day. On the other side of the Earth, it is nighttime.

3     The Earth's surface can be thought of as a giant circle. Circles can be measured in degrees. One whole circle is made up of 360 degrees. It takes the Earth 24 hours to turn in a circle. So when we divide 360 degrees by 24 hours, we see that the Earth rotates about 15 degrees each hour.

4     Each time zone is set up having 15 degrees of longitude. Longitude lines are the LONG lines you see on a globe. They run from the North Pole to the South Pole. They are like the LONG sides of a ladder. There are twenty-four time zones around the world.

5     Lines of longitude are also called meridians. This word came from the Latin word for midday. The sun crosses the meridians or lines of longitude at midday, or halfway between the times of sunrise and sunset. This is where we get the abbreviations for time of A.M. and P.M.

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