Wobbly mysteries of the universe

ON A dark night, in the northern hemisphere, it twinkles directly overhead. It is Polaris, the one star that (to human eyes) seems fixed in the sky, right above the North Pole.

For thousands of years before the advent of the compass, it was a boon to travellers, as they could use it to find their direction. In fact, it is only a temporary illusion that Polaris seems to stand above the North Pole. As the Earth wobbles around...