Polaris: Celebrated North Star and Triple Star System

Throughout the ages, Polaris has been described in various and interesting ways. The star has been called the “ship-star,” “immovable,” and “star of the sea.” Most of us today simply refer to it as our North Star. This is because it lies near the North Celestial Pole.

While it appears to be a single star, Polaris is actually a fascinating triple-star system situated approximately 433 light-years from Earth. The primary star, Polaris A, is a yellow supergiant many times larger and thousands of times more luminous than our Sun. It has two companions: Polaris Ab, orbiting very closely, and Polaris B, farther out and visible with a small telescope. Polaris A is also a Cepheid variable star, meaning its brightness subtly pulsates over several days — a characteristic that astronomers use to measure cosmic distances. So, our seemingly steady North Star is actually a complex and dynamic system!

My Observations

Over the years, I’ve glanced at Polaris quickly when aligning a telescope or camera, but I haven’t taken the time to really examine this multiple-star system. Due to local light pollution, I’m unable to make out several stars in the system, but I can still make out the double.

Key Stats

Constellation	Ursa Minor
Best Viewing	Anytime
Visual Magnitude	+1.9 | +9.0
Absolute Visual Magnitude	-3.61
Distance from Earth	433 ly
Separation	18.4″ | 2320 AU
Orbital Period	4 Days
Milky Way Location	Orion Spur
My Viewing Grade	A
Designtations	Alpha UMi, a UMI, Cynosura, SAO 308

Sources and Notes

Polaris Banner: DSS / Giuseppe Donatiello. This photo is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.

Sketch by Wayne McGraw