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Greenwich Mean Time |
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Latitude and longitude are means a ship can use to discover its location and to navigate safely. They are, of course, imaginary lines drawn on the face of the Earth. When looking at a map, latitude lines run horizontally. Latitude lines are also known as parallels since they are parallel and are an equal distant from each other. Each degree of latitude is approximately 111 km apart; there is a variation due to the fact that the earth is not a perfect sphere but slightly egg-shaped. Degrees latitude are numbered from 0° to 90° north and south. Zero degrees is the equator, the imaginary line which divides our planet into the northern and southern hemispheres. 90° north is the North Pole and 90° south is the South Pole. The vertical longitude lines are also known as meridians. They converge at the poles and are widest at the equator, 111 km apart. Zero degrees longitude is located at Greenwich, England (0°). The degrees continue 180° east and 180° west where they meet and form the International Date Line in the Pacific Ocean. Latitude and longitude work together to precisely locate points on the Earth's surface, degrees longitude and latitude have been divided into minutes (') and seconds ("). There are 60 minutes in each degree. Each minute is divided into 60 seconds. Seconds can be further divided into tenths, hundredths, or even thousandths. For example, the U.S. Capitol is located at 38°53'23"N , 77°00'27"W (38 degrees, 53 minutes, and 23 seconds north of the equator and 77 degrees, no minutes and 27 seconds west of the meridian passing through Greenwich, England). Before the 19th century each community used its own solar time. The development of rapid railway systems and the consequent confusion of schedules made necessary to establish a standard time. We employ 24 standard meridians of longitude 15º apart starting with the prime meridian through Greenwich, England. These meridians are theoretically the center of 24 time zones, in practice,the zones have in many cases been subdivided according to the inhabitans' convenience. We can say that time zones are a way of organizing time so that people living in a large country share the same time, just to make things easy. Some questions to make you think. Find an answer in the links on your right. 1. Why is Greenwich so important to the world? 2. Find the latitude and longitude in Greenwich. 3. What does GMT stand for? And UTC? do they mean the same? |
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