Time Zones The Earth rotates 15 degrees every hour. The idea behind multiple time zones

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.

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  noon in the Atlantic time zone
  
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  11 a.m. in the Eastern time zone
  
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  10 a.m. in the Central time zone
  
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  9 a.m. in the Mountain time zone
  
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  8 a.m. in the Pacific time zone.
  

Canadian Sir Sandford Fleming invented time zones in 1884 to address concerns about intercontinental railway transportation.

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  Since the earth rotates around its axis once every 24 hours, there are 24 time zones around the earth, with 1-hour difference between them. Since the earth rotates through 360^O in 24 hours, it rotates through 15^O of longitude in 1 hour (360^O / 24 = 15^O). Thus, each time zone is 15 degrees wide. Every place within a time zone has the same time, referred to as its standard time.
  
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  The Prime Meridian is the centre of a time zone that extends 7.5^O on either side. Time in this zone is called Universal Time (UT).
  
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  The Earth rotates from west to east. Time zones east of the Prime Meridian have local times ahead of UT. Time zones west of the Prime Meridian have local times behind UT. For example if the sun is directly above the Prime Meridian, the local time in the city of Berlin, which is one time zone east of UT, is 1 p.m. In Ottawa, which is five time zones west of the Prime Meridian, the time is 7 a.m. It will be five more hours before the sun appears directly over the 75^OW meridian which is the centre of the time zone where Ottawa is located.
  
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  Time zone shapes have been modified worldwide. China has one standard time for the whole country despite the fact that it covers more than 60^O of longitude. Canada has six standard time zones, although the boundaries do not follow the meridians of longitude.
  
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  Some places are located where time zones meet. St. John's, Newfoundland, at 52.5^OW, is located between the third and fourth time zones west of the prime meridian. Its time is 3.5 hours behind UT.
  
  
  

When sailors first sailed around the world, they returned home either a day ahead or a day behind those people who stayed. To correct this situation, the International Date Line was established. It runs between the North and South Pole, and generally follows the 180 line of longitude through the Pacific Ocean. It zigzags to avoid dividing land masses or island groups belonging to the same country. If you cross the date line moving westward, you add a day. If you cross the date line moving eastward, you lose a day. The time does not change unless the date line corresponds to a time zone boundary.

Many parts of the world change their time according to the season. During the summer, daylight-saving time is used to extend daylight hours into the evening when most people are awake. That is, the sun would set at 9 p.m. instead of 8 p.m. Theoretically, this time adjustment should reduce energy use since lights don't have to be turned on until later in the day. In Canada and the United States, daylight-saving time begins on the first Sunday in April and ends on the last Sunday in October. Other countries use different dates.

Early sailors determined their latitude by the angle of the sun above the horizon or by the position of the North Star (Polaris), but they had no practical way to find their longitude. In theory, longitude could be calculated if sailors knew their local time and the time in Greenwich. However, the pendulum clocks that were in use at the time did not work on a ship being tossed about by waves. In 1791, Englishman John Harrison developed the marine chronometer - spring-loaded clock that could keep time on a moving ship. Longitude was calculated in the following manner:

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  Exact local time: 7:00 am
  
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  Greenwich time: 12:00 noon
  
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  Since local time was five hours behind Greenwich, the location was west of the prime meridian.
  
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  5 hours = 75 degrees (5 x 15^o)
  
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  Current longitude: 75^o W of the prime meridian. Possible locations: Ottawa, Canada; Philadelphia. U.S.A.
  

Many people wonder why the Province of Newfoundland has a time zone that varies by the half hour rather than the standard one hour. While the system of Standard Time employs 24 meridians, and each are theoretically the centres of 24 Standard Time Zones, some adjustments have been made to the time zones for the convenience of inhabitants that lie within the zones. Newfoundland, (but not Labrador), lies squarely in the eastern half of its time zone, exactly three and a half hours from Greenwich. In 1963, the Newfoundland government attempted to bring the province into conformity with the other Atlantic provinces but withdrew in the face of stiff public opposition. Other countries that operate on the half hour time difference are Suriname, Iran, India, Sri Lanka, and Central Australia.

Summary -- Eight Time Zone Facts

1. 
   The Earth rotates about once every 24 hours. There are 24 hours in a day.
   
2. 
   The circumference of the Earth is 360°.
   
3. 
   Most time zones have a one hour time difference. The exception is Newfoundland Standard Time.
   

4. 
   Canada has six time zones: Newfoundland, Atlantic, Eastern, Central, Mountain and Pacific. When it is 12:30 p.m. in Newfoundland, it is
   

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  noon in the Atlantic time zone
  
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  11 a.m. in the Eastern time zone
  
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  10 a.m. in the Central time zone
  
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  9 a.m. in the Mountain time zone
  
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  8 a.m. in the Pacific time zone.
  

5. 
   Time Zones have approximately 15° of longitude from east to west.
   
6. 
   The world has 24 time zones (15° x 24 hours = 360°).
   
7. 
   Standard times starts at 0° longitude running through Greenwich, England. This is called the Greenwich Meridian or the Prime Meridian.
   
8. 
   Standard time was developed by Canadian Sir Sandford Fleming.