Any star that aligns with Earth's polar axis. In the northern hemisphere, the pole star currently is Polaris, also known as the North Star. Thanks to precession, however, Earth wobbles on its axis, which causes the north pole to aim at different stars over a cycle of about 26,000 years. The next pole star will be Gamma Cephei, one of the leading lights of the constellation Cepheus. Other future pole stars include Vega, the brightest star of Lyra, and Thuban, in Draco, which was used to help align the Great Pyramids of Giza. In the southern hemisphere, the pole is marked by Polaris Australis, also known as Sigma Octantis. It is much fainter than Polaris, however, so it's not as useful a marker.