Celestial pole

A celestial pole is one of the two points where Earth’s rotational axis, extended into space, intersects the celestial sphere. The north and south celestial poles mark the centers of apparent daily star rotation.

Earth's axis: An imaginary line through Earth’s center around which the planet rotates. Extending this axis in both directions defines the celestial poles.
Polaris: The brightest star in Ursa Minor, located close to the north celestial pole. Its small apparent circles make it a practical marker of the northern pole.
Axial precession: The slow change in the direction of Earth’s rotational axis, tracing a circle in the sky over about 26,000 years. Precession moves the celestial poles among different stars over millennia.
Geographic North Pole: The point on Earth’s surface where its rotational axis meets the northern hemisphere. It lies on Earth, unlike the north celestial pole’s projected position in the sky.
Celestial sphere: An imaginary sphere centered on an observer, onto which celestial objects are projected. The poles are the points where Earth’s extended axis meets this reference sphere.
Circumpolar star: A star that never sets below an observer’s horizon because it circles the celestial pole. Its visibility depends on the pole’s altitude and the observer’s latitude.
Nutation: Small periodic variations in the orientation of Earth’s rotational axis, superimposed on precession. These variations make the celestial poles oscillate slightly around their mean positions.
Magnetic North Pole: The moving point where Earth’s magnetic field is vertical and directed downward. It is defined by magnetism, not by Earth’s rotational axis.
Diurnal motion: The apparent daily movement of celestial objects across the sky, caused mainly by Earth’s rotation. Stars appear to circle the celestial poles as Earth turns.
Latitude: A geographic coordinate measuring angular distance north or south of Earth’s equator. The altitude of the visible celestial pole equals the observer’s latitude.

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