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.



Star concepts

Ch. 2
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