Earth rotates every 24 hours around an imaginary line that runs through the North and South poles. Gravitational pull caused by the Sun and Moon and the planet’s orbit, causes the axis to shift – but no one had ever measured it directly. To calculate this planetary wobble, researchers in Germany shone two lasers in opposite directions around a 4 metre-wide square loop buried 6 metres underground. The planet’s rotation means that the laser has to travel slightly farther in one direction than the other; the resultant change in the beams’ frequencies reveals the wobble. The results: Earth’s axis drifts every 435 days by as much as 6 metres.