Expedition 360 - Detailed Explanation of Antipodal Points and Great Circles

DETAILED EXPLANATION of ANTIPODAL POINTS & GREAT CIRCLES

To understand the significance of antipodal points in a true circumnavigation one must first define something called a Great Circle: the largest circle which can be drawn on the surface of globe by a plane cutting through the sphere at its centre. All longitudes are Great Circles because the plane cutting through every meridian of longitude cuts through the centre of globe as well as the north and south poles.

Following a Great Circle inevitably entails crossing a pair of Antipodal Points en route, and as such is the only way of ensuring a fair circumnavigation is achieved regardless of where on the planet a traveler starts from.

If you put planes through the latitudes, only the one through the equator will also cut through the centre of the globe and therefore can be said to be a Great Circle.

It would be easy if everyone could follow one of these Great Circles, but for practical reasons this is impossible.

Ironically employing a human powered method of travel offers perhaps the greatest opportunity of achieving one of these ideal circumnavigations.

The simplest and most effective way to prove that a circumnavigation attempt followed a Great Circle is to put the plane through any point of the prospective route and through the centre of the globe, and then to find the opposite point on that plane – the point called the antipode. Simply put, if somebody’s journey crosses at least one pair of antipodes, they traveled a Great Circle and can therefore claim a 'true' circumnavigation. This also ensures that:

> the equator is crossed at least twice
> a distance that is equal to or more than the length of the Equator (40.075 km) is traveled

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