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Did you know... Do you know why a Nautical mile is different from a statue mile? The answer is in the answer to the question "Why isn't there a KEY on a chart" (you know the little thing that shows how an inch is equal to a mile on a map). Lines of longitude come together at the poles. They touch there and yet at the equator they are almost 2 miles apart (about 0.7625 miles apart on our latitude). Lines of latitude are parallel. They are constantly spaced throughout the globe. Now Latitude (and longitude) divide the globe into 360 segments (degrees which can actually be measured at the poles using the longitude). And consistent with standard mathematics, each degree is divided into minutes and seconds. Well, some early chart maker realized that each minute of latitude was equal (well, almost equal) to a mile. So he didn't need a key because every chart will have latitude on both the right and left sides of the chart. A nautical mile is equal to 1.15077945 Statute miles or 1852 meters (6076.1 ft.). A statute mile = 0.86897624 nautical miles. So, a nautical mile is a minute of latitude and that is damn close to a mile. Why is nautical speed referred to as knots? Years ago a crude speedometer called a chip log was a light line that was knotted at regular intervals and weighted to drag in the water. It was tossed overboard over the stern as the pilot counted the knots that were let out during a specific period of time. The knots were spaced at a distance apart of 47 feet 3 inches (a distance found to produce the desired results) and the number of these knots which ran out while a 28-second sand glass emptied itself gave the speed of the ship in nautical miles per hour or knots. |
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