Antipodes

1. approaches to the antipode

We can start from the Latin etymology of the word: anti- “opposite” and -pode “the feet”. Originally the word designates an individual, who, located on the other side of the Earth, therefore has his feet exactly mirrored (see the scene in the film where the boy discovers the diver on the other side of the ice). The term was then clarified to designate the opposite point on the terrestrial globe, which is the furthest away. But what is the opposite of a point on a sphere? How to find it?

We can reason from the circle and first show that, if we travel around the circumference from a given point, the furthest point is one diameter away. From the sphere in volume, by passing a wire around it, we will look for the largest possible circle passing from a point. You can make marks on the wire to keep it as a reference. Children already know this largest circle, it is called the Equator. It allows us to divide the terrestrial sphere into two equal halves in thought, as a diameter divides the circle.

2. manipulations on the terrestrial globe

Now, if we pass this circle (the marked wire) through the north pole, we can define the south pole, which is the antipode of the north pole. If we return to the terrestrial globe to be assembled, we can notice that the plastic arm which holds the two assembled half-spheres hangs on one side to the north pole, on the other to the south pole. Since the north pole and south pole are antipodes, this means that this plastic arm measures exactly the path to go from one point to its antipode. We can use it as a “ruler” to find the antipode of any point on the globe (provided we ensure that we are tangent to the sphere, that is to say that the path follows the surface of the globe).

After this demonstration, we can apply our tool to search for several antipodean points. The region described in the film, which is one of the Eskimo living areas, can be located on the globe and we will verify that its antipode is somewhere on the edge of the Southern Ocean or in Antarctica.

In France, we will check that we fall off the coast of New Zealand. The Antipodes archipelago in New Zealand takes its name from the fact that it was thought to be the land closest to the antipode of London (it has since been calculated to be the antipode of a point located off the coast of Cherbourg).