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By Lindsay Craig

Objective: By the end of this lesson you will be able to determine the rough position of the time zones from your knowledge of longitude.

Reason:  It becomes important to know what the local time it is when communicating with someone in another time zone or when traveling to other time zone.   

Time zones are related directly to the Earth's longitude position.  In a day there are 24 hours, during this time the Earth makes one full rotation on it's axis.  From where we stand the sun and stars seem to move across the sky from east to west because the Earth rotates in the opposite direction. As we see it the sun rises in the east, climbs into the sky and sets in the west  only to rise again in the east and so on again and again.

Sketch of the globe showing longitude lines plus time of day, the equator, Virginia City, Nevada and Greenwich, EnglandThe adjacent image portrays only half of the Earth's surface.  We know that  the Earth has 360 longitude lines degree of angular separation around the globe.  For every hour that passes the Earth rotates eastward by 15degrees.

Imagine you are on the Prime Meridian, in "east" Greenwich, England; it is summer, at 5:00 AM,  and the sun is rising. A zone 15 degrees wide from the North Pole to the South Pole is at 5:00 AM at the very same moment.  To the west, the Atlantic is in the dark; so is most of  North America.  In Virginia City the time at that same moment is 10 PM, it is dark and most of the night is ahead.  There is an 8-hour time difference between the two cities and it will be eight more hours before it is 6 am in Virginia City.  Knowing this information, imagine yourself looking down on the Earth and you are above the North Pole, what direction would the Earth be spinning, counter clockwise or clockwise?

This image is a close approximation of where the time zone breaks exist.  If each line were viewed in actual detail, one would find that they are controlled by political boundaries such as state or country lines.  One country in particular, the Cook Islands in the South Pacific, really wanted to be different from the rest of the world and by declaration their time zone is one half hour off from the rest of the world. Because of the political boundaries imposed on time zones, the method used above is only good as an estimate of the time in any one locality. Further, the above model shows Virginia City on the west side of a particular time zone based on latitude, however the political boundaries imposed moved it into the time zone to the west .  This time zone is named Pacific Standard Time.  In the continental U.S. from west to east there are three other time zones, Mountain Standard Time, Central Standard Time, and Eastern Standard Time.

Activity #1: Print out or sketch the image above, flip over the printout and trace in the lines of longitude on the back side of the paper  by putting the printout to a window or light table.  Imagine you are looking at the backside of the image shown above and write in the times and the degrees of longitude for your tracing.  

Use this tracing to answer the following questions:

1. What is the time at 171 degrees west longitude when it is 12 PM in Virginia City?

2. Hawaii is between 150 and 165 degrees west longitude, what is the time there when it is 3 AM in west Greenwich?

3. When it is 4 PM in Hawaii what time is it at Virginia City?

4. Sydney, Australia is between 150-165 degrees east longitude; the Canary Islands are on the opposite side of the world between which longitude lines?

5. Examine the time zone that is 105-120 degrees west of Virginia City.  List the time when it is 5 AM in Virginia City?  Does this time zone have the date as that of Virginia City?

Click here to check your answers.

Activity #2. To learn more about current real world times across the globe visit these sites at:

http://www.cnn.com/WEATHER/worldtime/

http://atm.geo.nsf.gov/ieis/time.html

Write a paragraph about each web site describing what you observed.

Click here to take the Unit Test.

End of Lesson and End of Unit
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