Dave asked; > >I have a question that there may not be a definative answer to. OK, 1 >degree of latitude equals 60 nautical miles right? And, there are 360 >degrees in a circle right? How can there be 360 degrees of 60 nautical >miles each (degree) at both the equator and at latitude 60? The circle, of >course, is much much smaller at the 60 degree latitude. Position on the globe is measured by means of meridians and parallels. Meridians, which are imaginary lines drawn around the Earth through the poles, determine longitude. The meridian running through Greenwich, England, is the prime meridian of longitude, and all others are either east or west. Parallels, which are imaginary circles parallel with the equator, determine latitude. The length of a degree of longitude varies as the cosine of the latitude. At the equator a degree is 69.171 statute mi; this is gradually reduced toward the poles. Value of a longitude degree at the poles is zero. Latitude is reckoned by the number of degrees north or south of the equator, an imaginary circle on the Earth's surface everywhere equidistant between the two poles. According to the International Astronomical Union ellipsoid of 1964, the length of a degree of latitude is 68.708 statute mi at the equator and varies slightly north and south because of the oblate form of the globe; at the poles it is 69.403 statute mi. (Taken from my encyclopaedia) I believe the nautical mile was set as the length of one minute of arc of a great circle based on the assumption that the earth is a sphere (as I believe it was thought at the time the nautical mile was established). I suspect they chose the great circle because some kind of consistent measure was needed for navigation purposes. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Tue Sep 08 1998 - 05:24:20 PDT
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