Greenwich and World Time Zones

Preview of Main Ideas

Wait a minute! Although we would all like to stop the clock on some occasions, time waits for no one. This lesson will help students understand how the basis of time was determined, why there was a necessity to standardize time and time zones, and why Greenwich, England is where all time is measured from. Students will also become familiar with a time zone map and learn how to calculate time and calendar day for any location on the earth. People who travel to distant places or make long distance phone calls must be able to calculate time. This lesson has been developed to be used at anytime. However, it is particularly effective after studying Latitude and Longitude.

Connection with the Curriculum

This lesson could be used in a geography, social studies, language arts, or math class.

Teaching Level: Grades 5-8.

Objectives Classification Outline

Objective #1: The student will understand that the basis of time was determined by movements of the earth (revolution, rotation).

Essential Element: Environment and Society.

Standard #15: How physical systems affect human systems.

Knowledge Statement #1: Human responses to variations in physical systems.

Skill Set #5: Answer geographic questions.

Skill #1: Develop and present combinations of geographic information to answer geographic questions.

Theme: Regions, Movement, and Human Environment Interaction.

Objective #2: Students will understand the necessity to standardize time and time zones. The student will become familiar with a time zone map and be able to calculate time, and calendar day for any location.

Essential Element: The World in Spatial Terms.

Standard #1: How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective.

Knowledge Statement #2: How to make and use maps, globes, graphs, charts, models, and databases to analyze spatial distributions and patterns.

Skill Set #4: Analyze Geographic Information.

Skill #1: Interpret information obtained from maps, aerial photographs, satellite-produced images, and geographic information systems.

Theme: Location, Movement and Regions.

1. A classroom Atlas
2. A copy of Background Information (provided)
3. A copy of Understanding World time Zones fact sheet (provided)
4. A World Time Zone Map (provided)

DAY 1

1. Ask students where the basis of time came from. It was determined by the movements of the earth. A year from revolution – one new moon to the next – one complete moon orbit around the earth, 29 ½ days. A day from rotation – one complete turning of the earth on its axis, 24 hours.

2. Ask students how early navigators, or ship’s captains, like Columbus, or James Cook, determined their location, so as not to be lost at sea. They read and knew the stars in different constellations. They also used the sun. With the help of clocks or chronometers they measured solar noon at their location to noon at a prime location or meridian. (See Background Information – Determining longitude.)

3. Using an atlas have students locate the Prime Meridian and name the countries this imaginary line runs through. (See Understanding World Time Zones example #1, and #2.)
4. Have students locate the International Date Line (180 degree longitude line). Remind students that this imaginary line also divides the eastern from the western hemisphere and is important in measuring time and calendar days.

1. Remind students that because of rotation, in one hour, 1/24 of 360 degrees, or 15 degrees passes beneath the sun. The local or sun, time for any specific location depends on its longitude. Before the adoption of standard time, each city in the United States kept the local time of its own meridian. With the growth of railroads, these differences caused difficulties. (See background Information – Local Time to Time Zones.)
2. In 1883 the railroads of the United States and Canada adopted a system for standard time and delineated the first time zones in North America. Remind students that throughout a time zone, standard time is the same at any instant. This avoided the confusion of following local, or sun time. Ask the students how many time zones are in the contiguous U.S. (See Understanding World Time Zones example #9). Can the students figure out why there are 4 time zones. The 48 contiguous states covers approximately 60 degrees of longitude.
3. (See Understanding World Time Zones sheet examples #3, #4, and #5). Ask students why most nations agreed in 1884 to measure time from Greenwich. That is where all longitude is measured from, and historically the location of the Royal Observatory where ships would check their chronometers.
4. On the board draw a line representing the Prime Meridian. The Prime Meridian is in the center of this time zone. In other words the GMT Time Zone which is 15 degrees wide, extends from 7 ½ degrees west to 7 ½ degrees east of the Prime Meridian. The next time zone runs from 7 ½ degrees to 22 ½ degrees and so on adding 15 degrees for each zone. Have students look at the enclosed time zone map. Call their attention to the fact that the 15 degree longitude intervals are in the center of each of the time zones.
5. In general, the time in each zone is one hour earlier than a zone east of it. Have students observe this fact on the Time Zone Map by reading the times at the top of each time zone.
6. Give the students several locations and have them calculate the time. (See Understanding World time Zones sheet examples #6, #7, #8, #9).
7. Halfway around the globe from Greenwich, is the International Date Line (IDL). The Date Line roughly follows the 180^th meridian. A new day starts at the IDL and spreads to other locations as the earth turns. (See Understanding World time Zones example #11). Crossing the line at any time takes a person into a new day. With the use of a globe, point out the IDL and ask students if it is tomorrow, or yesterday just west of the line in the eastern hemisphere (it is tomorrow). Have students comment on how they might be able to relive a day in their life, perhaps a birthday. Have students calculate the date using several examples of crossing the IDL.
8. Every time zone is approximately 15 degrees wide. How can students account for the fact of some zones are more or less than 15 degrees and have a zigzag pattern. (See Understanding World Time Zones example #10).
9. Finally, comment on Irregular Time zones. For political or practical reasons not every country adheres to standard time zones. Their time may vary from a fraction of an hour to more. Generally though, most nations do abide by the accepted time zone pattern.

DAY 2

1. Pass out a copy of Understanding World Time Zones and briefly review the concepts. Have students ask questions or make comments on any of the statements.

2. Pass out and assign the World Time Zones Worksheet.

1. Have students investigate when and why Daylight Savings time was established.
2. Have students search as to what A.M. and P.M. stand for.
3. Have students report to the class how to convert A.M. and P.M. times to 24 hour time.
4. Have students who have experienced jet lag write about it.
5. Have students do research on early navigation or the development of precise chronometers.
6. Show slides of Greenwich, including the Royal Observatory, the Prime Meridian and the year 2000 countdown clock.

1. Quiz students on the facts they learned about Greenwich and the World Time Zones lesson.
2. Grade the World Time Zones Worksheet.
3. Have students write a paper as to why it was necessary to standardize time and time zones.
4. Have students summarize either orally or in writing how to calculate time using a Time Zone Map.

Understanding World Time Zones

1. The zero degree longitude line or the Prime Meridian passes through Greenwich, a suburb of London.
2. The Prime Meridian not only divides the eastern from the western hemisphere, but it is also where longitude and time is measured from.
3. It takes the earth 24 hours to make one complete rotation, the earth turns 360 degrees. Dividing 360 degrees by 24 hours gives you 15 degrees. Therefore, the earth is divided into 24 time zones, each of which is approximately 15 degrees of longitude wide.
4. In 1884, most nations agreed to standardize time and that Greenwich would be where all time is measured from.
5. Greenwich Mean Time (GMT) is whatever time it is in the main time zone, or the Prime Meridian Time Zone.
6. The map shows the time zones recognized today. Because Earth rotates from west to east, the hours grow earlier from east to west. When it is 3:00 P.M. in Moscow, it is noon in London.
7. To determine the standard time for any time zone in the world, add one hour for each time zone east of Greenwich. Subtract one hour for each time zone counted in a westerly direction from Greenwich.
8. Look at the time zone map. The numbers along the top of the map show what time it is in each of the other time zones when it is noon at the Prime Meridian.
9. Since the continental United States spans such a great distance, it has been divided into four standard time zones; Eastern, Central, Mountain and Pacific. When it is 7:00 A.M. in New York, it is 4:00 A.M. in Los Angeles.
10. Notice that the boundaries of the time zones zigzag across land areas. By general government agreement adjustments may be made to keep countries, provinces, or states in a single time zone to avoid confusion.
11. The International Date Line is at 180 degrees longitude. The time is the same on both sides of the International Date Line, but the day is different. West of the International Date Line (the eastern hemisphere) it is one day later than it is east of the International Date Line (the western hemisphere).

Background Information

Local Time – To Time Zones

The system of keeping time by the sun is called local time. When the sun was at its highest point in the sky, this was considered noon time. A location just one degree in longitude (less than 70 miles away) to the west would experience noon four minutes later, two degrees, eight minutes later. People used this system of local time for hundreds of years. Time was a local matter, and who cared if noon came earlier or later elsewhere?

Changes came in the way people lived. As new and faster methods of communication and travel developed, they began to see that they needed a more fixed system of time keeping. Railroads spanning the continents were getting into head-on collisions due to differences of opinion on the true time. Time zones were established because the era of increased travel made uniformity imperative. Since the majority of the world’s sea charts were being drawn up in England to the standards of the Royal Naval Observatory in Greenwich, this location became paramount. Ships would anchor outside the observatory on the Thames River and check their chronometers to the dropping of a large ball at 1 P.M. daily since 1833. The time ball is now regulated electronically.

Determining Longitude

In the 18^th century, the emphasis in research was on shipping. The British government gave a reward of 20,000 pounds to John Harrison for making a chronometer reliable enough to allow ships to determine their longitude within half a degree. Ships change their clocks as they move, using local time for navigation in determining their longitude. A four minute difference from local noon to the ships clock meant a variance of one degree of longitude.

Name ________________________________________

Date _________________________________________

Period _______________________________________

World Time Zones Worksheet

1. Where is all time measured from?

 

2. How many world time zones are there? Why?

 

3. Approximately how wide is each time zone?

 

4. Explain why time zone boundaries are not completely straight.

 

5. Name the four major United States time zones.

 

6. If the time in London is 12:00 P.M. GMT, what time is it in:

Chicago ___________________ Paris ___________________

Moscow __________________ Tokyo __________________

Buenos Aires ______________

7. If the time in Chicago is 12:15 P.M., what time is it in:

Chicago __________________ Paris ____________________

Moscow _________________ Tokyo ___________________

Buenos Aires ______________

8. It is 12:00 Midnight GMT. How much of the earth is in one calendar day, and how much is in another calendar day?

 

9. If it is Tuesday morning west of the International Date Line (eastern hemisphere), then what day is it east of the International Date Line (western hemisphere)?

 

10. If it is January 7, 10:00 P.M. in Chicago, what date and time is it in London?

 

11. If it is October 29, 3:00 A.M. in Sydney, what date and time is it in Chicago?

 

12. A man living in Honolulu, Hawaii on Tuesday 12:00 P.M. calls his cousin in Tokyo, Japan. What time is it in Tokyo? What calendar day is it?

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