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| Sunday, 8 May 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Why time changes from country to country
Although there are time differences between countries, we do have an international time, especially for administrative and political reasons. Greenwich Mean (or Meridian) Time (GMT) is the mean (average) time that the earth takes to rotate from noon-to-noon. GMT is World Time. It is the basis of every world time zone which sets the time of day and is at the centre of the time zone map. GMT sets the current time or official time around the globe. Most time changes are measured by GMT. Although GMT has been replaced by atomic time (UTC), it is still widely regarded as the correct time for every international time zone. Greenwich, England has been the home of Greenwich Mean Time (GMT) since 1884. GMT is sometimes called Greenwich Meridian Time because it is measured from the Greenwich Meridian Line at the Royal Observatory in Greenwich. In the past, when short distance travel dragged on for several days, nobody, except the astronomers, could understand that it was due to the fact that the solar time at the same moment is different from place to place. For instance, if in a certain place, the Sun is at noon position, in a more western place, the Sun has not yet reached the noon position. The contrary happens for a more eastern place. If two places are exactly aligned along the north-south direction, they have the same solar time, because they see the Sun forming at the same hour angle with the noon position. This alignment, defined geographically as meridian, is given by the half-circle passing these places and terminating at the terrestrial poles. Meanwhile, in several places in the world, hundreds of different times were adopted, each one corresponding to its own meridian. To simplify this situation, the Earth surface was divided into 24 adjacent, equal and equatorially perpendicular (at right angles to given line) wedges, called time zones, each one bounded by two meridians forming an hour angle at the poles. The mean solar time of the central meridian of each time zone was assigned by convention to all places belonging to the time zone. The actual boundaries between time zones often follow the frontiers of countries, which prevents one small country having two separate times.
The first time zone in the world was established by British railways on December 1, 1847-Greenwich Mean Time (GMT) being hand carried on chronometers. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Greenwich Observatory. Even though 98 per cent of Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880. On November 2, 1868, New Zealand officially adopted a standard time to be observed nationally, and was perhaps the first country to do so. It was based on the longitude 172 degrees 30' East of Greenwich, that is 11 hours 30 minutes ahead of Greenwich Mean Time. This standard was known as New Zealand Mean Time. Multiple time zones were first proposed by Charles F. Dowd about 1863 for American railroads, as a teacher to his students. In 1870, after consulting railroad officials in 1869, he proposed four ideal time zones, the first centered on Washington, DC, but by 1872 the first was centered 75 degrees west of Greenwich with geographic borders. American and Canadian railroads implemented their own version on November 18, 1883, when each railroad station clock was either advanced or delayed as noon, standard time, was reached within each time zone, east to west. Time zones were first proposed for the entire world by Canada's Sir Sandford Fleming in 1876 as an addition to the single 24-hour clock he proposed for the entire world (located at the centre of the Earth and not linked to any surface meridian). Most major countries had adopted hourly time zones by 1929. Even today, they have not been fully realized, with several time zones keeping a standard time that is not offset by a number of whole hours from Greenwich Mean Time. **** International Date Line Time is measured east and west of the prime meridian (0 degree longitude), which is an imaginary line that passes through Greenwich, England. East of Greenwich, the time advances by one hour for every 15 degrees of longitude. To the west, one hour is lost for every 15 degrees. At 180 degrees East, the time is 12 hours ahead of Greenwich, while at 180 degrees West, the time is 12 hours behind Greenwich. But, 180 degrees East and West are the same line. So, there is a difference of 24 hours between the two sides of this line, which is called the International Date Line.Crossing it from the west to east, you gain one whole day. But, when you go from east to west, you lose a day. The International Date Line does not follow the 180 degree line of
longitude exactly. It is adjusted so that it does not pass through land
areas. |
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| Politics | Produced by Lake House |
Have you ever wondered why different countries have different times? We
all live in one world, sharing the same sun and moon, then, why not have a
common time for every country? 
The Greenwich time zone, centred on the homonymous meridian, was taken
as reference time zone. In this way, the time zone right eastward
Greenwich is one hour in advance in comparison with universal time (UT
+01:00), while the time zone right westward Greenwich is 1 hour late (UT
-01:00) and so on for all the others. The time zones division was
officially adopted on November 1 1884 at the International Meridian
Conference held at Washington D.C. It can be immediately noted that for
political and administrative reasons, often the time zones are bounded by
state borders instead of meridians. 
