How to use it
- Type a place, or click the left globe. The pin can be dragged.
- The right globe turns to show the far side of the Earth, with the antipode marked.
- Drag either globe; the other follows.
5 practical uses
- Show a class what an antipode is on two globes at once.
- Settle where the tunnel from your town comes out.
- Compare a place with its opposite: season, time, land or sea.
- Explore the globe from both sides at the same time.
- Illustrate a story or a puzzle about the far side of the Earth.
The maths behind it
The antipode is (−φ, λ ± 180°). The two globes are kept opposite by setting the second globe's centre to the antipode of the first's. The fall time through a straight frictionless tunnel is T = π√(R/g), about 42 minutes, the same for any straight chord, from the harmonic motion of gravity inside a uniform sphere.
The tunnel
A straight tunnel through the centre of the Earth is 12,742 km long. In the old physics puzzle, if you could dig it and jump in, gravity would carry you to the far end in about 42 minutes, ignoring air, heat and the small matter of the core. Real tunnels are not straight down: the deepest hole ever drilled, the Kola Superdeep Borehole, reached 12 km, a fifth of a percent of the way.
See the antipode finder for what is at the far end and the nearest town to it.