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Because it is so close to the celestial north pole, its right ascension is changing rapidly due to the precession of Earth's axis, going from 2.5h in AD 2000 to 6h in AD 2100. Twice in each sidereal day Polaris's azimuth is true north; the rest of the time it is displaced eastward or westward, and the bearing must be corrected using tables or a ...
The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day (strictly, per sidereal day ).
The Purple Forbidden enclosure (紫微垣 Zǐ wēi yuán) is one of the San Yuan (三垣 Sān yuán) or Three Enclosures.Stars and constellations of this group lie near the north celestial pole and are visible all year from temperate latitudes in the Northern Hemisphere.
Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin / æ l ˈ d ɛr ə m ɪ n /, [10] [11] is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (ly) and drifting closer with a heliocentric radial velocity of about −16 km/s.
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.
Stars around the north celestial pole are grouped into three enclosures (垣, yuán). [1] The system of 283 asterisms under the Three Enclosures and Twenty-Eight Mansions was established by Chen Zhuo of the Three Kingdoms period, who synthesized ancient constellations and the asterisms created by early astronomers Shi Shen, Gan De and Wuxian. [2]
The Sanskrit term dhruva nakshatra (ध्रुव नक्षत्र, "polar star") has been used for Pole Star in the Mahabharata, personified as son of Uttānapāda and grandson of Manu, even though Polaris at the likely period of the recension of the text of the Mahabharata was still several degrees away from the celestial pole. [4] [5]
The Egyptian Pyramids were designed to have one side facing north, with an entrance passage geometrically aligned so that Thuban would be visible at night. [2] Due to the effects of precession, it will again be the pole star around the year AD 21000. It is a blue-white giant star of magnitude 3.7, 309 light-years from Earth.