The Polestar is

A pole star (or “polestar”) is a star that lies almost exactly on the extension of a planet’s rotational axis, so it appears to stay fixed in the sky through the night while every other star traces a circle around it — that fixed point is what lets an observer read off a direction from it.

For an observer in Earth’s Northern Hemisphere, that fixed point is occupied by Polaris, which sits within about a degree of the north celestial pole — the point directly above Earth’s North Pole. Because Polaris marks the direction Earth’s axis points, it is popularly called the “polestar” or the North Star, and has been used for centuries to find true north at night.

• No fixed star plays a comparable navigational role for south, east, or west in ordinary usage: those directions are not defined by any star sitting on Earth’s rotational axis, so “the South Star,” “the East Star,” and “the West Star” do not correspond to any real, practical navigational marker.

• The southern celestial pole does have a nearby faint naked-eye star, Sigma Octantis (about magnitude 5.5), sometimes informally called the southern pole star — but it is difficult to see except under dark, clear skies and far too inconspicuous for reliable navigation, unlike Polaris, which is why, without further qualification, “polestar” in everyday usage means the North Star.