Time+Zones

LONGITUDE AND TIME ZONES


 The theory behind time zones is quite simple:

 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 degrees in 24 hours, it must rotate through 15 degrees of longitude in 1 hour (360{degrees} = 24 = 15{degrees}).Therefore, each of the 24 time zones is 15 degrees wide. Every place within a time zone has the same time, referred to as its standard time.

 With the development of rapid railway transportation, in the second half of the 1800s, the need for standard time zones became obvious to Sir Sandford Fleming, Canada's most experienced railway surveyor and civil engineer. He wrote to the major governments of the world proposing the use of time zones. In 1884, an international conference was held in Washington, D. C. to approve Fleming's system. It adopted the meridian that runs through the Royal Observatory in Greenwich, England as the prime, or zero, meridian.

 The prime meridian is the centre of a time zone that extends 7.5 degrees on either side.Time in this zone is called universal time (UT) and the standard times in other zones are compared to it. Every 15 degrees, on either side of the prime meridian, is the centre of a time zone.  Since the earth rotates from west to east, time zones that are east of the prime meridian have local times that are ahead of UT. Time zones that are west of die prime meridian have local times that are 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 die prime meridian, die lime is 7 a.m. It will be five more hours before the sun appears directly over the 75{degrees}W meridian, which is the centre of the lime zone where Ottawa is located.

 Countries, however, may modify the shape of the lime zones and the standard (or legally recognized) time they use. For example, China has one standard time for the whole country despite the tact mat it covers more than 60{degrees} of longitude. Canada, on the other hand, has six standard time zones.The boundaries of the zones, however, do not follow exactly the meridians of longitude as discussed above.

The International Date Line

 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{degrees} line of longitude through the Pacific Ocean. It zigzags, however, to avoid dividing land masses or island groups that belong 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.

 Daylight-Saving Time

 Many parts of the world change their time according to the season. During the summer, daylight-saving tune is used to extend daylight hours into the evening when most people are awake. For example, the sun would set at 9 p.m. instead of 8 p.m., thereby cutting down on energy use same 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.

Activity
1. Why are there 24 time zones? 2. Why do we have time zones? Name 2 ways they can make our life easier! 3. Why do we have an international date line? <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">4. Why does the international date line zig-zag? <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">5. How does daylight savings time help us? <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">6. Calculate how many hours difference and whether it would be before or ahead of our time if; <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">a) you went 60 degrees to the west <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">b) you went 120 degrees to the east <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">c) you went 45 degrees to the east <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">d) you went 22 degrees to the north

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Extension
<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Find an internet site that calculates world time. Using the time that this class ends in the day, find out what time it would be in a major city (you decide) in each of the continents (except Antarctica).