Knowra Polaris Polaris Polaris, or Alpha Ursae Minoris, is a multiple-star system whose brightest member lies close to the north celestial pole and appears nearly fixed in the northern sky.
North celestial pole : The point in the northern sky where Earth’s rotation axis, extended outward, intersects the celestial sphere. Polaris lies about 0.6 degrees from this moving reference point.
Celestial navigation : Navigation that determines position or direction by observing the positions of celestial bodies. Its near-polar position makes Polaris a practical direction marker for northern navigators.
Ursa Minor : A northern constellation containing Polaris at the end of the Little Dipper’s handle. Polaris is its brightest star and marks the handle’s endpoint.
Cepheid variable star : A pulsating giant or supergiant whose repeating brightness changes are tied to its luminosity. Polaris Aa’s Cepheid behavior raises questions about how its pulsation has changed over time.
Earth's axial precession : The slow change in the direction of Earth's rotation axis, completing a cycle in roughly 26,000 years. Precession shifts the pole, so Polaris is only a temporary pole star.
Latitude : The angular distance of a location north or south of Earth's equator, measured in degrees. In the Northern Hemisphere, Polaris’s altitude above the horizon approximates local latitude.
Ursa Major : A large northern constellation that includes the Big Dipper asterism. The Big Dipper’s pointer stars help locate Polaris in the sky.
Stellar evolution : The changes in a star’s structure and properties over its lifetime, driven by nuclear fuel use and internal physics. Polaris’s changing pulsation period may reflect its evolving position in the instability strip.
Circumpolar star : A star that never sets below the horizon for observers at a particular latitude. Polaris appears circumpolar throughout most of the Northern Hemisphere.
Astrolabe : An instrument that models the sky and measures celestial altitudes for astronomy, timekeeping, and navigation. Astrolabes could use Polaris and nearby stars to estimate celestial positions.
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