Polaris has not always been the North Star, because the celestial pole is slowly moving in a 26,000-year-long circle that follows a wobble in the Earth's axis called precession. Right now, the celestial pole is actually still drawing closer to Polaris, but on March 24, 2100, it will be as close as it ever will come, just 27.15 arc minutes or slightly less than the moon's apparent diameter. Over the centuries, different stars have marked the north celestial pole. Kochab, for instance, the brightest star in the bowl of the Little Dipper, was the North Star at the time of Plato, around 400 B.C.