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Knots being phased out?
On Fri, 01 Dec 2006 20:18:10 GMT, Bruce in Alaska
wrote: In article , krj wrote: Peter Bennett wrote: On Fri, 01 Dec 2006 14:12:52 GMT, keith_nuttle wrote: Since the nautical mile is defined as one minute of latitude, I doubt it will ever disappear in earth based navigation. The Nautical Mile was originally based on a minute of latitude, but the length of a minute of latitude varies with latitude, so an International Nautical Mile is now defined as 1852 metres exactly, or 6076.11549 US feet, approximately, according to Bowditch. I believe that the nautical mile is based on the minute of LONGITUDE not latitude. Longitude doesn't vary with changes in latitude (or attitude). That's why when you are using paper charts (remember those) you measure the distance with your dividers on the longitude scale on the east or west side of the chart. krj Hmmmmm..... I think you have your terms "Wrapped around the Axle" here.... Nautical Miles is based on "Minute of Latitude" which does NOT change since the distance from the Equater to the Poles is ALWAYS the SAME, from any place on the EQUATER. Therefor, when dividing that distance in Degrees, MInutes, and Seconds, will ALWAYS produce the same Unit Lengths. Where as Longitude is the cicumfrence of the earth at the equater divided into Degrees, Minutes, and Seconds, and that DOES change Unit length as you move closer to the Poles. Longitude is marked on the bottom and top of Maps, where Latitude is marked on the right and left had edges of Maps. One ALWAYS uses the Latitude markings for distance because they do NOT change Unit Length, EVER..... Bruce in alaska Since the earth is not a perfect sphere, the length of a minute of latitude _does_ vary slightly with latitude - Bowditch has a table showing the lengths of a minute of Lat and Long for various latitudes. I vaguely recall a minute of latitude varies by 300 ft or so from equator to pole (don't recall which end is longer), and is only a nautical mile at about 44 degrees. |
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