Positions on earth are defined by their longitude (how far east or west you are) and latitude (how far north or south you are). both latitude and longitude are angles. a nautical mile is one minute of degree of longitude along the equator. (a nautical mile is a little more than a regular mile.) traveling at xx knots means traveling at xx nautical miles per hour. suppose you fly in a lockheed sr-71 (the fastest jet ever built) along the equator at a speed of 1,800 knots (roughly the top speed of the sr-71). ignoring issues of refueling and such, it takes you equation editorequation editor hours to fly once around the world. you leave after breakfast and are back in time for a late dinner. some airplane!