Time ZonesWhy Have Time Zones?

Everyone on the planet wants the sun to be at its highest point in the sky (crossing the meridian) at noon. If there were just one time zone, this would be impossible because the Earth rotates 15 degrees every hour. The idea behind multiple time zones is to divide the world into 24 15-degree slices and set the clocks accordingly in each zone. All of the people in a given zone set their clocks the same way, and each zone is one hour different from the next.

The Concept of Standard Time

The concept of standard time was adopted in the late 19th century in an attempt to end the confusion that was caused by each community's use of its own solar time. Some such standard became increasingly necessary with the development of rapid railway systems and the consequent confusion of schedules that used scores of different local times kept in separate communities. (Local time varies continuously with change in longitude.)

The need for a standard time was felt most particularly in the United States and Canada, where several extensive railway routes passed through places that differed by several hours in local time.

Sir Sandford Fleming, a Canadian railway planner and engineer, outlined a plan for worldwide standard time in the late 1870s. Following this initiative, in 1884 delegates from 27 nations met in Washington, D.C., for the Meridian Conference and agreed on a system basically the same as that now in use.

Prime Meridian and UTC

The present system employs 24 standard meridians of longitude (lines running from the North Pole to the South, at right angles to the Equator) 15º apart, starting with the prime meridian through Greenwich, England. These meridians are theoretically the centres of 24 standard time zones; in practice, the zones have in many cases been subdivided or altered in shape for the convenience of inhabitants.

Time is the same throughout each zone and differs from the international basis of legal and scientific time, Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC), by an integral number of hours; minutes and seconds are the same.

In a few regions, however, the legal time kept is not that of one of the 24 standard time zones because half-hour or quarter-hour differences are in effect there.

All time zones are measured from a starting point centered at England's Greenwich Observatory. This point is known as the Greenwich Meridian or the Prime Meridian. Time at the Greenwich Meridian is known as Greenwich Mean Time (GMT) or Universal Time (UTC). The Eastern time zone in Canada is designated as GMT minus five hours. When it is noon in the Eastern time zone, it is 5 p.m. at the Greenwich Observatory. The International Date Line (IDL) is located on the opposite side of the planet from the Greenwich Observatory.

Why is the Greenwich Observatory such a big deal? A bunch of astronomers declared the Greenwich Observatory to be the prime meridian at an 1884 conference.

How Time Zones Work

Each time zone is then theoretically 15 degrees wide, corresponding to a one-hour difference in mean solar time. The shape of time zones is changed, in practice, to match internal and international borders. Civil time changes by one hour forward and backward respectively for every 15 degrees east or west of the Greenwich Meridian. One would need to divide the longitude, in degrees, by 15 to find the appropriate time zone, in hours. For example:

At 150 degrees west (or 150° W) longitude, the time should be 150 degrees divided by 15 degrees = 10 hours behind Coordinated Universal Time (UTC/GMT) (or UTC-10).

At 75 degrees east (or 75° E) longitude, the time would be 75 degrees divided by 15 degrees = 5 hours ahead of UTC/GMT (or UTC+5).

Not All Time Zones 150 or 1 Hour

Some countries have non-standard time zones, usually with a 30-minute offset (a few have a 45-minute offset). For example, the time zone in India is five hours and 30 minutes (UTC+5:30) ahead of UTC.

Time zones’ boundaries are irregular mainly because of political factors, and so this has been a subject of criticism. Time zones can be determined by how countries’ and states’ borders are positioned. Individual zone boundaries are not straight because they are adjusted for the convenience and desires of local populations. Moreover, some geographically large countries, such as India and China, use only one time zone but other large countries, such as Canada and the United States, have more than one time zone.

Canada uses six primary time zones. From east to west they are Newfoundland Time Zone, Atlantic Time Zone, Eastern Time, Central Time Zone, Mountain Time Zone, and the Pacific Time Zone.

Military Time Zone Codes and Abbreviations

Military time zones are used worldwide for both military and civilian purposes. They represent each of the twenty four time zones in use around the world, including Coordinated Universal Time (UTC) which is represented by the Zulu Time Zone.The current assignment of time zone names is based upon the NATO phonetic alphabet. This system has helped to eliminate some confusion which resulted in previous proposals.

Each time zone name corresponds to a unique one character letter assigned to that time zone. However, because some letters such as "D and B" or "M and N" could be easily confused in verbal communications, the time zone name itself is most often used. So in this example Delta would be used when referring to UTC + 4 rather than the letter "D."

Time Zones Assignment

1. In which Canadian time zone is each one of the following cities?

a) Toronto ______________________ b) Ottawa _________________________

c) Vancouver ______________________ d) Winnipeg _________________________

e) Montreal ______________________ f) St. John’s _________________________

g) Edmonton ______________________ h) Regina _________________________

2. When it is 8:00 AM in Toronto determine the time each one of the following cities:

a) Vancouver _______________________ b) London, England _______________________

c) New York City _______________________ d) Moscow ________________________

e) Tel Aviv _______________________ f) Athens ________________________

g) Beijing _______________________ h) Miami ________________________

i) Paris _______________________ j) Los Angeles ________________________

3. If you drive from Toronto to Calgary will you have to reset your watch and if so, by how much and will it be forward or backward? ____________________________________________________________________________________________

4. If it takes your flight 3 hours to go from Toronto to Vancouver and you left Toronto at 7:00 PM, what time will you arrive in Vancouver local time? ____________________________________________________________________________________________

5. Through Which ocean does the International Date Line predominately pass through? ________________________

6. When it is 9:00 PM in Tokyo on Wednesday, what time and date is it in Toronto? ____________________________

7. When it is 9:00 PM in Toronto on Friday, what time and date is it in Tokyo? ________________________________

8. Who set up the system of standard time zones and what was this person’s nationality? ____________________________________________________________________________________________

9. All time zones are measured from this starting point __________________________________________________

10. Along what line of longitude is the International Date Line generally on? ___________________________________

11. How many degrees of longitude per time zone (theoretically)? ___________________________________________

12. What is the military call sign for the time zone Toronto is located in? ______________________________________

13. This time zone is referred to as the Coordinated Universal Time (UTC) and all other time zones are compared to it ____________________________________________________________________________________________

14. Why does Canada need more than one time zone? ___________________________________________________

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15. It is 6:00 PM in Greenwich, what time is it 900 west of there? ____________________________________________

16. It is 6:00 PM in Greenwich, what time is it 1050 east of there? ___________________________________________

17. How many time zones in Canada? ________________________________________________________________

18. How many time zones in China? __________________________________________________________________

19. Why do you think there is this number of times zones in China? _________________________________________ ____________________________________________________________________________________________

20. Why was the concept of time zones introduced? _____________________________________________________

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