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A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth , a pole star would lie directly overhead when viewed from the North or the South Pole .
With an apparent magnitude that fluctuates around 1.98, [3] it is the brightest star in the constellation and is readily visible to the naked eye at night. [16] The position of the star lies less than 1° away from the north celestial pole, making it the current northern pole star.
The celestial north pole is located very close (less than 1° away) to the pole star (Polaris or North Star), so from the Northern Hemisphere, all circumpolar stars appear to move around Polaris. Polaris itself remains almost stationary, always at the north (i.e. azimuth of 0°), and always at the same altitude (angle from the horizon), equal ...
Over the course of an evening in the Northern Hemisphere, circumpolar stars appear to circle around the north celestial pole. Polaris (within 1° of the pole) is the nearly stationary bright star just to the right of center in this star trail photo.
The rotation axis of the Earth describes, over a period of 25,700 years, a small blue circle among the stars near the top of the diagram, centered on the ecliptic north pole (the blue letter E) and with an angular radius of about 23.4°, an angle known as the obliquity of the ecliptic. The direction of precession is opposite to the daily ...
Constellation positions change throughout the year due to night on Earth occurring at gradually different portions of its orbit around the Sun. As Earth rotates toward the east, the celestial sphere appears to rotate west, with stars circling counterclockwise around the northern pole star and clockwise around the southern pole star. [22]
The International Astronomical Union (IAU) defines the north pole of a planet or any of its satellites in the Solar System as the planetary pole that is in the same celestial hemisphere, relative to the invariable plane of the Solar System, as Earth's north pole. [1] This definition is independent of the object's direction of rotation about its ...
From most of the Northern Hemisphere, Polaris (the North Star) and the other stars of the constellation Ursa Minor circles counterclockwise around the north celestial pole and remain visible at both culminations (as long as the sky is clear and dark enough).