The South Star is the star which is circumpolar to the South Pole (as Polaris, the North Star, is for the North Pole), and can thus be reliably used for navigation. The present South Star is Sigma Octantis, which is very faint.
Polaris Australis is not as useful as Polaris Borealis for navigation ; σ Octantis is faint, however, the constellation Crux, the Southern Cross, points towards the south pole
