IDENTIFY TIME ZONES AND CALCULATE TIME.

Longitude and time zones

In lesson 1 you learned the terms longitude, meridian, and prime meridian. In addition to location, these terms also relate to the rotation of the earth and the time of day. This is how it works: because it takes the earth twenty-four hours to rotate, the earth is divided into twenty-four time zones, each one hour apart. Each time zone covers about 15º of longitude.

By international agreement, longitude is measured from the prime meridian in Greenwich, England. When the sun is exactly overhead in Greenwich, which is 0º longitude, it is noon there. The time zones west of 0º are earlier than Greenwich, and the time zones east of 0º are later than Greenwich. Every 15º represents one hour, so if it is 3:00 p.m. in Greenwich, then it is 2:00 p.m.15º west of Greenwich, and it is 4:00 p.m. 15º east of Greenwich.

Figure 3.4.1, A map illustrating the twenty-four time zones in the world. ("Standard Time Zones of the World," CIA World Factbook, 2007. https://www.cia.gov/cia/publications/factbook/reference_maps/time_zones.html)

Take a look at Figure 3.4.1. Can you find New York City? Now find Chicago. If it is 1:00 p.m. in New York, what time is it in Chicago? If you said noon, you are right. Chicago is one time zone west of New York; therefore it is one hour earlier in Chicago than it is in New York. Now find Caracas, Venezuela. It is one time zone to the east of New York; this means Caracas is one hour later than New York. If it is 1:00 p.m. in New York, then it is 2:00 p.m. in Caracas.

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