polaris

Polaris, also known as the North Star or Alpha Ursae Minoris, is the brightest star in the northern constellation Ursa Minor. It lies very close to the direction of the Earth’s northern axis, so it has served as a navigational reference for travelers for centuries. Because of the precession of the equinoxes, Polaris is not exactly at the north celestial pole but currently lies within about 0.7 degrees of it and will remain a near-pole star for many centuries.

Polaris is a yellow-white supergiant with spectral type F7Ib. It is a classical Cepheid variable with a small brightness variation, cycling every about 3.97 days. Its apparent magnitude is approximately 1.97, and it is the brightest star in Ursa Minor. At an estimated distance of about 433 light-years (roughly 133 parsecs), Polaris is one of the closest Cepheid variables to Earth, a fact that makes it important for calibrating the Cepheid period–luminosity relation.

Polaris is a multiple-star system. The primary component (Polaris A) has at least one faint visual companion, and interferometric measurements have uncovered additional close companions, indicating a hierarchical system.

In addition to its scientific interest, Polaris serves as a prominent guide for stargazers and navigators in the northern hemisphere, anchoring the end of the Little Dipper’s handle and providing orientation toward true north.