Photo credit M. Menefee, source Space.com
Polaris, often called the North Star, is actually a binary star and shows the variability of a Cepheid variable. The binary nature affects its pulsation, and it pulsates in more than one mode. Polaris' companion is called Polaris B, and in 2006 a second companion, Polaris Ab was visually confirmed by the Hubble Space Telescope. Polaris is a bright yellow supergiant with radius 46 +/- 3 solar radii and approximately 2200 times the solar luminosity. The luminosity of Polaris varies at a period of 3.97 days and it orbits Polaris B with a period of approximately 30 years. Its distance is 110 pc. The smaller companion has enabled the determination of approximate masses of 5.0 +/- 1.5 solar masses for Polaris A and 1.36 +/- .61 solar masses for Polaris Ab. Their separation is about 18.5 AU.
Polaris is a second magnitude star which is also referred to as Alpha Ursae Minoris of constellation Ursu Minor. The north celestial pole is in Ursa Minor and very close to Polaris.