Polaris, the North Star, is both a binary star and a Cepheid star. A binary star is a pair of stars that share a gravitational pull. A Cepheid star pulsates, illuminating in varying degrees of brightness.
Polaris is part of a three-star system, but one star is much farther away than the other two. The star closest to Polaris is part of the binary system, as the stars interact with one another. Scientists measure the mass of Polaris by the gravitational pull of the two stars. The flickering of Polaris also helps astronomers calculate distances to other objects in the night sky. A star only exists as a Cepheid for a short time before stabilizing.