Pole star

A long exposure (45 min.) photo of Polaris and neighbouring stars, taken at Ehrenbürg (Franconia), 2001.

A pole star or polar star is a star, preferably bright, closely aligned to the axis of rotation of an astronomical object.

With regard to planet Earth, the pole star refers to Polaris (Alpha Ursae Minoris), a magnitude 2 star aligned approximately with its northern axis, and a pre-eminent star in celestial navigation.

History

The path of the north celestial pole amongst the stars due to the effect of precession, with dates shown
The path of the south Celestial pole amongst the stars due to the effect of precession

In classical antiquity, Beta Ursae Minoris (Kochab) was closer to the celestial north pole than Alpha Ursae Minoris. While there was no naked-eye star close to the pole, the midpoint between Alpha and Beta Ursae Minoris was reasonably close to the pole, and it appears that the entire constellation of Ursa Minor, in antiquity known as Cynosura (Greek Κυνοσούρα "dog's tail") was used as indicating the northern direction for the purposes of navigation by the Phoenicians.[1] The ancient name of Ursa Minor, anglicized as cynosure, has since itself become a term for "guiding principle" after the constellation's use in navigation.

Alpha Ursae Minoris (Polaris) was described as ἀειφανής "always visible" by Stobaeus in the 5th century, when it was still removed from the celestial pole by about 8°. It was known as scip-steorra ("ship-star") in 10th-century Anglo-Saxon England, reflecting its use in navigation. At around the same time, in the Hindu Puranas, it became personified under the name Dhruva ("immovable, fixed").

In the medieval period, Polaris was also known as stella maris "star of the sea" (from its use for navigation at sea), as in e.g. Bartholomeus Anglicus (d. 1272), in the translation of John Trevisa (1397):

"by the place of this sterre place and stedes and boundes of the other sterres and of cercles of heven ben knowen: therefore astronomers beholde mooste this sterre. Then this ster is dyscryved of the moste shorte cercle; for he is ferre from the place that we ben in; he hydeth the hugenesse of his quantite for unmevablenes of his place, and he doth cerfifie men moste certenly, that beholde and take hede therof; and therfore he is called stella maris, the sterre of the see, for he ledeth in the see men that saylle and have shyppemannes crafte."[2]

Polaris was associated with Marian veneration from an early time, Our Lady, Star of the Sea being a title of the Blessed Virgin. This tradition goes back to a misreading of Saint Jerome's translation of Eusebius' Onomasticon, De nominibus hebraicis (written ca. 390). Jerome gave stilla maris "drop of the sea" as a (false) Hebrew etymology of the name Maria. This stilla maris was later misread as stella maris; the misreading is also found in the manuscript tradition of Isidore's Etymologiae (7th century);[3] it probably arises in the Carolingian era; a late 9th-century manuscript of Jerome's text still has stilla, not stella,[4] but Paschasius Radbertus, also writing in the 9th century, makes an explicit reference to the "Star of the Sea" metaphor, saying that Mary is the "Star of the Sea" to be followed on the way to Christ, "lest we capsize amid the storm-tossed waves of the sea."[5]

The name stella polaris was coined in the Renaissance, even though at that time it was well recognized that it was several degrees away from the celestial pole; Gemma Frisius in the year 1547 determined this distance as 3°7'.[6] An explicit identification of Mary as stella maris with the North Star (Polaris) becomes evident in the title Cynosura seu Mariana Stella Polaris (i.e. "Cynosure, or the Marian Polar Star"), a collection of Marian poetry published by Nicolaus Lucensis (Niccolo Barsotti de Lucca) in 1655.

Other Languages
Afrikaans: Poolster
العربية: نجم القطب
asturianu: Estrella Polar
català: Estel polar
español: Estrella polar
français: Étoile polaire
Frysk: Poalstjer
हिन्दी: ध्रुव तारा
íslenska: Pólstjarna
italiano: Stella polare
Bahasa Melayu: Bintang kutub
Nederlands: Poolster
日本語: 北極星
ਪੰਜਾਬੀ: ਧਰੂ ਤਾਰਾ
پنجابی: قطبی تارا
português: Estrela Polar
română: Stea polară
русский: Поляриссима
shqip: Ylli Polar
sicilianu: Puddara
Simple English: Pole star
srpskohrvatski / српскохрватски: Polarna zvijezda
suomi: Napatähti
svenska: Polstjärna
українська: Поляриссима
Tiếng Việt: Sao Bắc cực
粵語: 極星
中文: 極星