World’s Time Zones
6-1.2 (6)
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 method 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 18th 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.
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).
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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