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Stephen gave the only constantspeed "great circle" solution, following the equator at about Mach 2.2. However, there are many other solutions, including some possible for nonsupersonic planes. For instance, near the spring or fall equinox even a small plane could fly around the North Pole in a circle and do the same thing. Theoretically if you were right by the Pole you could walk (except your head would be too high, and the Sun would be skimming along the horizon so that "setting" would not be apparent) Any point on Earth can be the starting point for some solutions. Any altitude will work (with minor adjustments to airspeed) Good Hunting!  


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