Circumnavigation

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Circumnavigation – literally, "navigation of a circumference" – refers to travelling all the way around an island, a continent, or the entire planet Earth.

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Global circumnavigation

In principle, if a person walks completely around either Pole, they will have crossed all meridians, but this is not generally considered a "circumnavigation." A basic definition of a global circumnavigation would be a route which covers at least a great circle, and in particular one which passes through at least one pair of points antipodal to each other.[1] In practice, different definitions of world circumnavigation are used, in order to accommodate practical constraints depending on the method of travel. Since the planet is a sphere, a trip from one Pole to the other, and back again, would technically be a circumnavigation, but practical difficulties generally preclude such a voyage.

For the wealthy, long voyages around the world, such as was done by Ulysses S. Grant, became possible in the 19th century, and the World Wars moved vast numbers of troops around the planet. However, it was later improvements in technology and rising incomes that made such trips relatively common.

Nautical

The map on the right shows, in red, a typical sailing circumnavigation of the world by the trade winds and the Suez and Panama canals; overlaid in yellow are the points antipodal to all points on the route. It can be seen that the route roughly approximates a great circle, and passes through two pairs of antipodal points. This is a route followed by many cruising sailors; the use of the trade winds makes it a relatively easy sail, although it passes through a number of zones of calms or light winds. But sometimes the winds would pick up quickly, causing many deaths during this sail period.

In yacht racing, a round-the-world route approximating a great circle would be quite impractical, particularly in a non-stop race where use of the Panama and Suez Canals would be impossible. Yacht racing therefore defines a world circumnavigation to be a passage of at least 21,600 nautical miles (40,000 km) in length which crosses the equator, crosses every meridian and finishes in the same port as it starts.[2] The map on the left shows the route of the Vendée Globe round-the-world race in red; overlaid in yellow are the points antipodal to all points on the route. It can be seen that the route does not pass through any pairs of antipodal points. Since the winds in the higher latitudes predominantly blow west-to-east it can be seen that there is an easier route (west-to-east) and a harder route (east-to-west) when circumnavigating by sail; this difficulty is magnified for square-rig vessels.

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