Additional Material for Time Zones Study Guide

1. Who first discovered a method of keeping time?       The ancient Greeks

2. Through mathematics and observation, they theorized the earth was a sphere.

3. They divided the earth into 360 segments that they called degrees or 360°.

4. Vertical lines called meridians (longitude) were devised to mark the segments on the globe.

5. Earth makes one complete 360° rotation each 24 hours.

6. How far does the earth turn in one hour?   360 ÷ 24 = 15

Therefore, the earth travels 15° in one hour and each segment between meridians is 15° wide.

7. Each fifteen degree segment, marked off by a line of longitude (or a meridian), represents a new time zone on the international time zone map.

8. The time zone segments begin at 0° longitude which is the Prime Meridian.

9. The Prime Meridian runs through Greenwich, England where the Royal Naval Observatory is located.

10. This time zone is called Greenwich Mean Time; all time begins, ends, and is measured here.

11.  In order to mathematically discover the difference in times around the world you simply count the meridian segments between two destinations, divide by fifteen, and the answer will be how many hours they are apart in time. For example, there are 5 meridian segments between Greenwich, England and Langley, Virginia, USA. Multiply 5 by 15° (the width of each meridian) and the answer is 75. Then divide 75 by 15° (the movement of the earth per hour) and you get 5. Therefore, it is 5 hours between Greenwich and Langley (which is in the eastern time zone of the U.S.)

12. Until the 1880’s, there was no such thing as time zones in the U.S.

13. Most cities and towns during that period kept time by the sun.

14. Some towns used time balls that they mounted on tall buildings and lowered slowly each day to mark the passing of one calendar day. But none of this helped to synchronize time between towns.

15. There was as many time zones as there were cities.

16.  In 1883, the railroads (which had become the most powerful businesses in the country) took it upon themselves to create four set time zones for the country in order that they would no longer have chaos in driving the trains across the country. 

ORIGINAL RAILROAD MAP ISSUED IN 1897 by the BURLINGTON RAILROAD

17. The railroads created our current time zones – Eastern, Central, Mountain and Pacific – in order that the trains could stay on schedule for passengers and goods, and they would have fewer wrecks.

18. The time zones in the U.S. were not created along straight meridian lines; they were created along county lines or political and business lines according to the needs of the railroads.


U.S. TIME ZONE MAP

INTERNATIONAL TIME ZONE MAP (zoom the screen up to see more detail on this map)