A pole star is a visible

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

that is approximately aligned with the

axis of rotation Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...

of an

astronomical body An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical object, physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ...

; that is, a star whose apparent position is close to one of the

celestial pole The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at ...

s. On

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, a pole star would lie directly overhead when viewed from the

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...

or the

South Pole The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the point in the Southern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True South Pole to distinguish ...

. Currently, Earth's pole stars are

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinisation of names, Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an ...

(Alpha Ursae Minoris), a bright

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

2 star aligned approximately with its northern axis that serves as a pre-eminent star in

celestial navigation Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface ...

, and a much dimmer magnitude 5.5 star on its southern axis, Polaris Australis (Sigma Octantis). From around 1700 BC until just after 300 AD, Kochab (Beta Ursae Minoris) and Pherkad (Gamma Ursae Minoris) were twin northern pole stars, though neither was as close to the pole as Polaris is now.

History

A method to find Polaris at 5x the distance of Merak and Dubhe of Ursa Major

classical antiquity Classical antiquity, also known as the classical era, classical period, classical age, or simply antiquity, is the period of cultural History of Europe, European history between the 8th century BC and the 5th century AD comprising the inter ...

Beta Ursae Minoris Kochab , Bayer designation Beta Ursae Minoris (β Ursae Minoris, abbreviated β UMi, Beta UMi), is the brightest star in the bowl of the Little Dipper asterism (which is part of the constellation of Ursa Minor), and only slightly fainter ...

(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 Ursa Minor (, contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern celestial hemisphere, northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of ...

, in antiquity known as '' Cynosura'' (Greek Κυνόσουρα "dog's tail"), was used as indicating the northern direction for the purposes of navigation by the

Phoenicians Phoenicians were an ancient Semitic group of people who lived in the Phoenician city-states along a coastal strip in the Levant region of the eastern Mediterranean, primarily modern Lebanon and the Syrian coast. They developed a maritime civi ...

. 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 (transliterated as ''aeiphanes'') meaning "always above the horizon", "ever-shining" by

Stobaeus Joannes Stobaeus (; ; 5th-century AD), from Stobi in Macedonia (Roman province), Macedonia, was the compiler of a valuable series of extracts from Greek authors. The work was originally divided into two volumes containing two books each. The tw ...

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 Anglo-Saxon England or early medieval England covers the period from the end of Roman Empire, Roman imperial rule in Roman Britain, Britain in the 5th century until the Norman Conquest in 1066. Compared to modern England, the territory of the ...

, reflecting its use in navigation. In the Vishnu

Purana Puranas (Merriam-Webster's Encyclopedia of Literature
(1995 Editio ...

, it is personified under the name ''

Dhruva Dhruva (Sanskrit: ध्रुव, , Literal translation, lit. "''unshakeable, immovable, fixed or eternal"'') was an Asceticism, ascetic devotee of Vishnu mentioned in the Vishnu Purana and the Bhagavata Purana. The Sanskrit term ''dhruva na ...

'' ("immovable, fixed"). 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 Gemma Frisius (; born Jemme Reinerszoon; December 9, 1508 – May 25, 1555) was a Dutch physician, mathematician, cartographer, philosopher, and instrument maker. He created important globes, improved the mathematical instruments of his day ...

in the year 1547 determined this distance as 3°8'. 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.

Precession of the equinoxes

In 2022 Polaris' mean

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

was 89.35 degrees North; (at epoch J2000 it was 89.26 degrees N). So it appears due north in the sky to a precision better than one degree, and the angle it makes with respect to the true horizon (after correcting for refraction and other factors) is within a degree of the latitude of the observer. The celestial pole will be nearest Polaris in 2100. Due to the

precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's Rotation around a fixed axis, rotational axis. In the absence of precession, the astronomical body's orbit would show ...

(as well as the stars' proper motions), the role of North Star has passed from one star to another in the remote past, and will pass in the remote future. In 3000 BC, the faint star

Thuban Thuban (), with Bayer designation Alpha Draconis or α Draconis, is a binary star system in the northern constellation of Draco. A relatively inconspicuous star in the night sky of the Northern Hemisphere, it is historically signifi ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Draco was the North Star, aligning within 0.1°

distance Distance is a numerical or occasionally qualitative measurement of how far apart objects, points, people, or ideas are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two co ...

from the celestial pole, the closest of any of the visible pole stars. However, at magnitude 3.67 (fourth magnitude) it is only one-fifth as bright as Polaris, and today it is invisible in light-polluted urban skies. During the 1st millennium BC,

(Kochab) was the bright star closest to the celestial pole, but it was never close enough to be taken as marking the pole, and the Greek navigator

Pytheas Pytheas of Massalia (; Ancient Greek: Πυθέας ὁ Μασσαλιώτης ''Pythéās ho Massaliōtēs''; Latin: ''Pytheas Massiliensis''; born 350 BC, 320–306 BC) was a Greeks, Greek List of Graeco-Roman geographers, geographer, explo ...

in ca. 320 BC described the celestial pole as devoid of stars. In the

Roman era In modern historiography, ancient Rome is the Roman people, Roman civilisation from the founding of Rome, founding of the Italian city of Rome in the 8th century BC to the Fall of the Western Roman Empire, collapse of the Western Roman Em ...

, the celestial pole was about equally distant between Polaris and Kochab. The precession of the equinoxes takes about 25,770 years to complete a cycle. Polaris' mean position (taking account of

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In o ...

and

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

) will reach a maximum

of +89°32'23", which translates to 1657" (or 0.4603°) from the celestial north pole, in February 2102. Its maximum apparent declination (taking account of

nutation Nutation () is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference fra ...

and aberration) will be +89°32'50.62", which is 1629" (or 0.4526°) from the celestial north pole, on 24 March 2100.Jean Meeus, Mathematical Astronomy Morsels Ch. 50; Willmann-Bell 1997 Precession will next point the north celestial pole at stars in the northern constellation Cepheus. The pole will drift to space equidistant between Polaris and

Gamma Cephei Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the northern constellation of Cepheus (constellation), Cepheus. The primary (designated Gamma Cephei A, officially name ...

("Errai") by 3000 AD, with Errai reaching its closest alignment with the northern celestial pole around 4200 AD. Iota Cephei and

Beta Cephei Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-y ...

will stand on either side of the northern celestial pole some time around 5200 AD, before moving to closer alignment with the brighter star Alpha Cephei ("Alderamin") around 7500 AD. Precession will then point the north celestial pole at stars in the northern constellation Cygnus. Like Beta Ursae Minoris during the 1st millennium BC, the bright star closest to the celestial pole in the 10th millennium AD, first-magnitude

Deneb Deneb () is a blue supergiant star in the constellation of Cygnus. It is the brightest star in the constellation and the 19th brightest in the night sky, with an apparent magnitude slightly varying between +1.21 and +1.29. Deneb is one ...

, will be a distant 7° from the pole, never close enough to be taken as marking the pole, while third-magnitude

Delta Cygni Delta Cygni is a binary star of a combined third-magnitude in the constellation of Cygnus (constellation), Cygnus. It is also part of the Northern Cross (asterism), Northern Cross Asterism (astronomy), asterism whose brightest star is D ...

will be a more helpful pole star, at a distance of 3° from celestial north, around 11,250 AD. Precession will then point the north celestial pole nearer the constellation

Lyra , from ; pronounced: ) is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra was often represented on star ...

, where the second brightest star in the

northern celestial hemisphere The northern celestial hemisphere, also called the Northern Sky, is the Northern Hemisphere, northern half of the celestial sphere; that is, it lies north of the celestial equator. This arbitrary sphere diurnal motion, appears to rotate westward ...

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, and ...

, will be a pole star around 14,500 AD, though at a distance of 5° from celestial north. Precession will eventually point the north celestial pole nearer the stars in the constellation

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

, pointing towards

Tau Herculis Tau Herculis, a name Latinized from τ Herculis, is a variable star in the northern constellation of Hercules. It has a blue-white hue and is visible to the naked eye at night with an apparent visual magnitude that fluctuates around 3.9 ...

around 18,400 AD. The celestial pole will then return to the stars in constellation Draco (Thuban, mentioned above) before returning to the current constellation, Ursa Minor. When Polaris becomes the North Star again around 27,800 AD, due to its

it then will be farther away from the pole than it is now, while in 23,600 BC it was closer to the pole. Over the course of Earth's 26,000-year

axial precession In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In parti ...

cycle, a series of bright

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

stars (an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

up to +6; a full moon is −12.9) in the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

will hold the transitory title of North Star. While other stars might line up with the north

during the 26,000 year cycle, they do not necessarily meet the naked eye limit needed to serve as a useful indicator of north to an Earth-based observer, resulting in periods of time during the cycle when there is no clearly defined North Star. There will also be periods during the cycle when bright stars give only an approximate guide to "north", as they may be greater than 5° of

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

removed from direct alignment with the north celestial pole. The 26,000 year cycle of North Stars, starting with the current star, with stars that will be "near-north" indicators when no North Star exists during the cycle, including each star's average brightness and closest alignment to the north celestial pole during the cycle:

Southern pole star (South Star)

Currently, there is no South Pole Star like

, the so-called ''North Star''. Sigma Octantis is the closest near

naked-eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. In astronomy, the naked eye m ...

star to the south celestial pole, but at

5.47 it is barely visible on a clear night, making it less useful for casual navigational or astronomy alignment purposes. It is a yellow giant 294

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s from Earth. Its

angular separation Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

from the pole is about 1° (). The

Southern Cross CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system to ...

constellation functions as an approximate southern pole constellation, by pointing to where a southern pole star would be. At the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

, it is possible to see both Polaris and the Southern Cross. The celestial south pole is moving toward the Southern Cross, which has pointed to the south pole for the last 2000 years or so. As a consequence, the constellation is no longer visible from subtropical northern latitudes, as it was in the time of the

ancient Greeks Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically re ...

. Around 200 BC, the star Beta Hydri was the nearest bright star to the celestial south pole. Around 2800 BC,

Achernar Achernar is the brightest star in the constellation of Eridanus and the ninth-brightest in the night sky. It has the Bayer designation Alpha Eridani, which is Latinized from α Eridani and abbreviated Alpha Eri or α Eri. The name Ac ...

was only 8 degrees from the south pole. All In A Spin Star trail

In the next 7500 years, the south celestial pole will pass close to the stars Gamma Chamaeleontis (4200 AD), I Carinae, Omega Carinae (5800 AD), Upsilon Carinae, Iota Carinae (Aspidiske, 8100 AD) and Delta Velorum (Alsephina, 9200 AD). From the eightieth to the ninetieth centuries, the south celestial pole will travel through the False Cross. Around 14,000 AD

Canopus Canopus is the brightest star in the southern constellation of Carina (constellation), Carina and the list of brightest stars, second-brightest star in the night sky. It is also Bayer designation, designated α Carinae, which is Rom ...

will have a declination of –82°, meaning it will rise and set daily for latitudes between 8°S and 8°N, and will not rise to viewers north of this latter 8th parallel north. Precession and proper motion mean that

Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word (Latin script: ), meaning 'glowing' or 'scorching'. The star is designated Canis Majoris, Latinized to Alpha Canis Majoris, and abbr ...

will be a future southern pole star: at 88.4° S declination in the year 66,270 AD; and 87.7° S declination in the year 93,830 AD.

Other planets

Pole stars of other planets are defined analogously: they are stars (brighter than 6th magnitude, i.e., visible to the naked eye under ideal conditions) that most closely coincide with the projection of the planet's axis of rotation onto the celestial sphere. Different planets have different pole stars because their axes are oriented differently. (See

Poles of astronomical bodies The poles of astronomical bodies are determined based on their axis of rotation in relation to the celestial poles of the celestial sphere. Astronomical bodies include stars, planets, dwarf planets and small Solar System bodies such as comets a ...

In religion and mythology

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.

Bartholomaeus Anglicus Bartholomaeus Anglicus (before 1203–1272), also known as Bartholomew the Englishman and Berthelet, was an early 13th-century Scholastic of Paris, a member of the Franciscan order. He was the author of the compendium ''De proprietatibus rerum ...

(d. 1272), in the translation of

John Trevisa 350px, John Trevisa (or John of Trevisa; ; fl. 1342–1402 AD) was a Cornish writer and professional translator. Trevisa was born at Trevessa in the parish of St Enoder in mid-Cornwall, in Britain and was a native Cornish speaker. He was edu ...

(1397): Polaris was associated with Marian veneration from an early time,

Our Lady, Star of the Sea Our Lady, Star of the Sea is an ancient title for Mary, the mother of Jesus. The words ''Star of the Sea'' are a translation of the Latin title . The title has been in use since at least the early medieval period. Purportedly arising from a sc ...

being a title of the Blessed Virgin. This tradition goes back to a misreading of

Saint Jerome Jerome (; ; ; – 30 September 420), also known as Jerome of Stridon, was an early Christian priest, confessor, theologian, translator, and historian; he is commonly known as Saint Jerome. He is best known for his translation of the Bible ...

's translation of

Eusebius Eusebius of Caesarea (30 May AD 339), also known as Eusebius Pamphilius, was a historian of Christianity, exegete, and Christian polemicist from the Roman province of Syria Palaestina. In about AD 314 he became the bishop of Caesarea Maritima. ...

' '' 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 Isidore ( ; also spelled Isador, Isadore and Isidor) is a masculine given name. The name is derived from the Greek name ''Isídōros'' (Ἰσίδωρος, latinized ''Isidorus'') and can literally be translated to 'gift of Isis'. The name has survi ...

's ''

Etymologiae (Latin for 'Etymologies'), also known as the ('Origins'), usually abbreviated ''Orig.'', is an etymological encyclopedia compiled by the influential Christian bishop Isidore of Seville () towards the end of his life. Isidore was encouraged t ...

'' (7th century); it probably arises in the Carolingian era; a late 9th-century manuscript of Jerome's text still has ''stilla'', not ''stella'', but

Paschasius Radbertus Paschasius Radbertus (785–865) was a Carolingian theologian and the abbot of Corbie, a monastery in Picardy founded in 657 or 660 by the queen regent Bathilde with a founding community of monks from Luxeuil Abbey. His most well-known and inf ...

, 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."''stella maris, sive illuminatrix Maria, inter fluctivagas undas pelagi, fide ac moribus sequenda est, ne mergamur undis diluvii'' PL vol. 120
p. 94
In

Mandaean cosmology Mandaean cosmology is the Gnostic conception of the universe in the religion of Mandaeism. Mandaean cosmology is strongly influenced by ancient near eastern cosmology broadly and Jewish, Babylonian, Persian, Greek, Manichaean and other Near ...

, the Pole Star is considered to be auspicious and is associated with the

World of Light In Mandaeism, the World of Light or Lightworld () is the primeval, transcendental world from which Tibil and the World of Darkness emerged. Description *The Great Life ('' Hayyi Rabbi'' or Supreme God/ Monad) is the ruler of the World of Ligh ...

("heaven").

Mandaeans Mandaeans (Mandaic language, Mandaic: ࡌࡀࡍࡃࡀࡉࡉࡀ) ( ), also known as Mandaean Sabians ( ) or simply as Sabians ( ), are an ethnoreligious group who are followers of Mandaeism. They believe that John the Baptist was the final and ...

face north when praying, and

temples A temple (from the Latin ) is a place of worship, a building used for spiritual rituals and activities such as prayer and sacrifice. By convention, the specially built places of worship of some religions are commonly called "temples" in Engli ...

are also oriented towards the north. On the contrary, the south is associated with the

World of Darkness ''World of Darkness'' is a series of tabletop role-playing games, originally created by Mark Rein-Hagen for White Wolf Publishing. It began as an annual line of five games in 1991–1995, with ''Vampire: The Masquerade'', ''Werewolf: The Apocaly ...

References

External links

*
Star trails around Polaris
{{DEFAULTSORT:Pole Star Articles containing video clips Navigation Star types