Polaris of the Snows
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Polaris is a
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
in the northern
circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest po ...
of
Ursa Minor Ursa Minor (Latin: 'Lesser Bear', contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, ...
. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
that fluctuates around 1.98, it is the brightest star in the constellation and is readily visible to the
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. Vision corrected to norma ...
at night. The position of the star lies less than away from the north
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 a ...
, making it the current northern
pole star A pole star or polar star is a star, preferably bright, nearly aligned with the axis of a rotating astronomical body. Currently, Earth's pole stars are Polaris (Alpha Ursae Minoris), a bright magnitude-2 star aligned approximately with its ...
. The stable position of the star in the Northern Sky makes it useful for
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation ...
. As the closest
Cepheid variable A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid vari ...
its distance is used as part of the
cosmic distance ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible o ...
. The revised ''
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial ob ...
''
stellar parallax Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant objects, and a basis for determining (through trigonometry) the distance of the object. Created by the different orbital p ...
gives a distance to Polaris of about , while the successor mission ''Gaia'' gives a distance of about . Calculations by other methods vary widely. Although appearing to the naked eye as a single point of light, Polaris is a triple
star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speaking ...
, composed of the primary, a
yellow supergiant A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous. Yellow supergiants ...
designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is in a wider orbit with Polaris B. The outer pair AB were discovered in August 1779 by
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...
, where the 'A' refers to what is now known to be the Aa/Ab pair.


Stellar system

Polaris Aa is an
evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...
yellow supergiant A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous. Yellow supergiants ...
of
spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
F7Ib with 5.4
solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es (). It is the first classical
Cepheid A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid varia ...
to have a mass determined from its orbit. The two smaller companions are Polaris B, a F3
main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar ...
star orbiting at a distance of (AU), and Polaris Ab (or P), a very close F6 main-sequence star with a mass of . Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a
reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...
of his own, one of the best telescopes of the time. In January 2006,
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
released images, from the Hubble telescope, that showed the three members of the Polaris ternary system. The variable
radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...
of Polaris A was reported by
W. W. Campbell William Wallace Campbell (April 11, 1862 – June 14, 1938) was an American astronomer, and director of Lick Observatory from 1901 to 1930. He specialized in spectroscopy. He was the tenth president of the University of California from 1923 to ...
in 1899, which suggested this star is a binary system. Since Polaris A is a known cepheid variable, J. H. Moore in 1927 demonstrated that the changes in velocity along the line of sight were due to a combination of the four-day pulsation period combined with a much longer
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
and a large
eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...
of around 0.6. Moore published preliminary
orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...
of the system in 1929, giving an
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
of about 29.7 years with an eccentricity of 0.63. This period was confirmed by
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distan ...
studies performed by B. P. Gerasimovič in 1939. As part of her doctoral thesis, in 1955 E. Roemer used radial velocity data to derive an orbital period of 30.46 y for the Polaris A system, with an eccentricity of 0.64. K. W. Kamper in 1996 produced refined elements with a period of and an eccentricity of . In 2019, a study by R. I. Anderson gave a period of with an eccentricity of . There were once thought to be two more widely separated components—Polaris C and Polaris D—but these have been shown not to be physically associated with the Polaris system.


Observation


Variability

Polaris Aa, the supergiant primary component, is a low-amplitude
Population I During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926: Baade noticed th ...
classical Cepheid variable Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to ...
, although it was once thought to be a type II Cepheid due to its high
galactic latitude The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an a ...
. Cepheids constitute an important
standard candle The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible o ...
for determining distance, so Polaris, as the closest such star, is heavily studied. The variability of Polaris had been suspected since 1852; this variation was confirmed by
Ejnar Hertzsprung Ejnar Hertzsprung (; Copenhagen, 8 October 1873 – 21 October 1967, Roskilde) was a Danish chemist and astronomer. Career Hertzsprung was born in Frederiksberg, Denmark, the son of Severin and Henriette. He studied chemical engineering at Cop ...
in 1911. The range of brightness of Polaris is given as 1.86–2.13, but the amplitude has changed since discovery. Prior to 1963, the amplitude was over 0.1 magnitude and was very gradually decreasing. After 1966, it very rapidly decreased until it was less than 0.05 magnitude; since then, it has erratically varied near that range. It has been reported that the amplitude is now increasing again, a reversal not seen in any other Cepheid. The period, roughly 4 days, has also changed over time. It has steadily increased by around 4.5 seconds per year except for a hiatus in 1963–1965. This was originally thought to be due to secular redward (lower temperature) evolution across the Cepheid instability strip, but it may be due to interference between the primary and the first-
overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...
pulsation modes. Authors disagree on whether Polaris is a fundamental or first-overtone pulsator and on whether it is crossing the instability strip for the first time or not. The temperature of Polaris varies by only a small amount during its pulsations, but the amount of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than 50  K to at least 170 K, may be related to the orbit with Polaris Ab. Research reported in ''
Science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence ...
'' suggests that Polaris is 2.5 times brighter today than when
Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...
observed it, changing from third to second magnitude. Astronomer Edward Guinan considers this to be a remarkable change and is on record as saying that "if they are real, these changes are 100 times larger than
hose A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called '' pipes'' (the word ''pipe'' usually refers to a rigid tube, whereas a hose is usually a flexible one), or more generally ...
predicted by current theories of
stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...
".


Role as pole star

Because Polaris lies nearly in a direct line with the
Earth's rotation Earth's rotation or Earth's spin is the rotation of planet Earth around its own axis, as well as changes in the orientation of the rotation axis in space. Earth rotates eastward, in prograde motion. As viewed from the northern polar star Po ...
al axis "above" the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Ma ...
—the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for
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 o ...
and for
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Hist ...
. The elevation of the star above the horizon gives the approximate
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
of the observer. In 2018 Polaris was 0.66° away from the pole of rotation (1.4 times the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
disc) and so revolves around the pole in a small circle 1.3° in diameter. It will be closest to the pole (about 0.45 degree) soon after the year 2100. Because it is so close to the celestial north pole, its
right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the ( hour circle of the) point in question above the earth. When pair ...
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 Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coor ...
Polaris'
azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...
is true north; the rest of the time it is displaced eastward or westward, and the bearing must be corrected using tables or a
rule of thumb In English, the phrase ''rule of thumb'' refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various t ...
. The best approximation is made using the leading edge of the "
Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl" ...
" asterism in the constellation Ursa Major. The leading edge (defined by the stars Dubhe and Merak) is referenced to a clock face, and the true azimuth of Polaris worked out for different latitudes. The apparent motion of Polaris towards and, in the future, away from the celestial pole, is 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 rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In partic ...
. The celestial pole will move away from α UMi after the 21st century, passing close by
Gamma Cephei Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the constellation of Cepheus. The primary (designated Gamma Cephei A, officially named Errai , the traditional name of ...
by about the 41st century, moving towards
Deneb Deneb () is a first-magnitude star in the constellation of Cygnus, the swan. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and the ...
by about the 91st century. The celestial pole was close to
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 significa ...
around 2750 BC, and during
classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...
it was slightly closer to
Kochab Beta Ursae Minoris (β Ursae Minoris, abbreviated β UMi, Beta UMi), formally named Kochab , 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 tha ...
(β UMi) than to Polaris, although still about from either star. It was about the same angular distance from β UMi as to α UMi by the end of
late antiquity Late antiquity is the time of transition from classical antiquity to the Middle Ages, generally spanning the 3rd–7th century in Europe and adjacent areas bordering the Mediterranean Basin. The popularization of this periodization in English h ...
. The Greek navigator
Pytheas Pytheas of Massalia (; Ancient Greek: Πυθέας ὁ Μασσαλιώτης ''Pythéas ho Massaliōtēs''; Latin: ''Pytheas Massiliensis''; born 350 BC, 320–306 BC) was a Greek geographer, explorer and astronomer from the Greek colony ...
in ca. 320 BC described the celestial pole as devoid of stars. However, as one of the brighter stars close to the celestial pole, Polaris was used for navigation at least from late antiquity, and described as ἀεί φανής (''aei phanēs'') "always visible" by
Stobaeus Joannes Stobaeus (; grc-gre, Ἰωάννης ὁ Στοβαῖος; fl. 5th-century AD), from Stobi in Macedonia, was the compiler of a valuable series of extracts from Greek authors. The work was originally divided into two volumes containin ...
(5th century), and it could reasonably be described as ''stella polaris'' from about the
High Middle Ages The High Middle Ages, or High Medieval Period, was the periodization, period of European history that lasted from AD 1000 to 1300. The High Middle Ages were preceded by the Early Middle Ages and were followed by the Late Middle Ages, which ended ...
. On his first trans-Atlantic voyage in 1492,
Christopher Columbus Christopher Columbus * lij, Cristoffa C(or)ombo * es, link=no, Cristóbal Colón * pt, Cristóvão Colombo * ca, Cristòfor (or ) * la, Christophorus Columbus. (; born between 25 August and 31 October 1451, died 20 May 1506) was a ...
had to correct for the "circle described by the pole star about the pole". In Shakespeare's play
Julius Caesar Gaius Julius Caesar (; ; 12 July 100 BC – 15 March 44 BC), was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war, an ...
, written around 1599, Caesar describes himself as being "as constant as the northern star", though in Caesar's time there was no constant northern star. Polaris was referenced in
Nathaniel Bowditch Nathaniel Bowditch (March 26, 1773 – March 16, 1838) was an early American mathematician remembered for his work on ocean navigation. He is often credited as the founder of modern maritime navigation; his book '' The New American Practical Navi ...
's 1802 book, ''
American Practical Navigator ''The American Practical Navigator'' (colloquially often referred to as ''Bowditch''), originally written by Nathaniel Bowditch, is an encyclopedia of navigation. It serves as a valuable handbook on oceanography and meteorology, and contains usef ...
'', where it is listed as one of the navigational stars.


Names

The modern name ''Polaris''
IAU Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
is shortened from
New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...
''stella polaris'' " polar star", coined in the Renaissance when the star had approached the celestial pole to within a few degrees.
Gemma Frisius Gemma Frisius (; born Jemme Reinerszoon; December 9, 1508 – May 25, 1555) was a Frisian physician, mathematician, cartographer, philosopher, and instrument maker. He created important globes, improved the mathematical instruments of his ...
, writing in 1547, referred to it as ''stella illa quae polaris dicitur'' ("that star which is called 'polar'"), placing it 3° 8' from the celestial pole. In 2016, the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
organized a
Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Polaris'' for the star α Ursae Minoris Aa. In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and the entire constellation of
Ursa Minor Ursa Minor (Latin: 'Lesser Bear', contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, ...
was used for navigation rather than any single star. Polaris moved close enough to the pole to be the closest naked-eye star, even though still at a distance of several degrees, in the early medieval period, and numerous names referring to this characteristic as polar star have been in use since the medieval period. In Old English, it was known as ''scip-steorra'' ("ship-star") ; In the Old English rune poem, the T-rune is apparently associated with "a circumpolar constellation", or the planet Mars. In the Hindu
Puranas Purana (; sa, , '; literally meaning "ancient, old"Merriam-Webster's Encyclopedia of Literature (1995 Edition), Article on Puranas, , page 915) is a vast genre of Indian literature about a wide range of topics, particularly about legends an ...
, it became personified under the name ''
Dhruva Dhruva (Sanskrit: ध्रुव, , lit. "''unshakeable, immovable, or fixed"'') was an ascetic devotee of Vishnu mentioned in the Vishnu Purana and the Bhagavata Purana. The Sanskrit term ''dhruva nakshatra'' (ध्रुव नक्ष ...
'' ("immovable, fixed"). In the later medieval period, it became associated with the Marian title of ''Stella Maris'' "Star of the Sea" (so in
Bartholomeus 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' ...
, c. 1270s) An older English name, attested since the 14th century, is lodestar "guiding star", cognate with the Old Norse ''leiðarstjarna'', Middle High German ''leitsterne''. The ancient name of the constellation Ursa Minor, ''Cynosura'' (from the Greek "the dog's tail"), became associated with the pole star in particular by the early modern period. An explicit identification of Mary as ''stella maris'' with the polar star (''Stella Polaris''), as well as the use of ''Cynosura'' as a name of the star, is 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. Its name in traditional pre-Islamic Arab astronomy was ''al-Judayy'' الجدي ("the kid", in the sense of a juvenile
goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...
le Chevreau"in Description des Etoiles fixes), and that name was used in
medieval Islamic astronomy Islamic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age (9th–13th centuries), and mostly written in the Arabic language. These developments mostly took place in the Middle ...
as well. In those times, it was not yet as close to the north celestial pole as it is now, and used to rotate around the pole. It was invoked as a symbol of steadfastness in poetry, as "steadfast star" by Spenser.
Shakespeare William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
's sonnet 116 is an example of the symbolism of the north star as a guiding principle: " oveis the star to every wandering bark / Whose worth's unknown, although his height be taken." In ''
Julius Caesar Gaius Julius Caesar (; ; 12 July 100 BC – 15 March 44 BC), was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war, an ...
'', he has
Caesar Gaius Julius Caesar (; ; 12 July 100 BC – 15 March 44 BC), was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war, an ...
explain his refusal to grant a pardon by saying, "I am as constant as the northern star/Of whose true-fixed and resting quality/There is no fellow in the firmament./The skies are painted with unnumbered sparks,/They are all fire and every one doth shine,/But there's but one in all doth hold his place;/So in the world" (III, i, 65–71). Of course, Polaris will not "constantly" remain as the north star due to
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 oth ...
, but this is only noticeable over centuries. In Inuit astronomy, Polaris is known as ''Niqirtsuituq'' ( syllabics: ). It is depicted on the
flag A flag is a piece of fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term ''flag'' is also used to refer to the graphic design empl ...
and
coat of arms A coat of arms is a heraldic visual design on an escutcheon (i.e., shield), surcoat, or tabard (the latter two being outer garments). The coat of arms on an escutcheon forms the central element of the full heraldic achievement, which in its ...
of the
Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...
Inuit territory of
Nunavut Nunavut ( , ; iu, ᓄᓇᕗᑦ , ; ) is the largest and northernmost territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the '' Nunavut Act'' and the '' Nunavut Land Claims Agreement Act'' ...
, as well as on the
flag A flag is a piece of fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term ''flag'' is also used to refer to the graphic design empl ...
of the U.S. state of
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
. In traditional
Lakota Lakota may refer to: * Lakota people, a confederation of seven related Native American tribes *Lakota language, the language of the Lakota peoples Place names In the United States: * Lakota, Iowa * Lakota, North Dakota, seat of Nelson County * La ...
star knowledge, Polaris is named "Wičháȟpi owáŋžila". This translates to "The Star that Sits Still". This name comes from a
Lakota Lakota may refer to: * Lakota people, a confederation of seven related Native American tribes *Lakota language, the language of the Lakota peoples Place names In the United States: * Lakota, Iowa * Lakota, North Dakota, seat of Nelson County * La ...
story in which he married Tapun San Win "Red Cheeked Woman". However she fell from the heavens, and in his grief he stared down from "waŋkátu" (the above land) forever. The Plains Cree call the star in Nehiyawewin: ''acâhkos êkâ kâ-âhcît'' "the star that does not move" ( syllabics: ). In Mi'kmawi'simk the star is named ''Tatapn''.


Distance

Many recent papers calculate the distance to Polaris at about 433
light-years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
(133 parsecs), based on parallax measurements from the
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial ob ...
astrometry satellite. Older distance estimates were often slightly less, and research based on high resolution spectral analysis suggests it may be up to 110 light years closer (323 ly/99 pc). Polaris is the closest
Cepheid variable A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid vari ...
to Earth so its physical parameters are of critical importance to the whole astronomical distance scale. It is also the only one with a dynamically measured mass. The ''Hipparcos'' spacecraft used
stellar parallax Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant objects, and a basis for determining (through trigonometry) the distance of the object. Created by the different orbital p ...
to take measurements from 1989 and 1993 with the accuracy of 0.97 
milliarcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...
s (970 microarcseconds), and it obtained accurate measurements for stellar distances up to 1,000 pc away. The Hipparcos data was examined again with more advanced error correction and statistical techniques. Despite the advantages of Hipparcos
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Hist ...
, the uncertainty in its Polaris data has been pointed out and some researchers have questioned the accuracy of Hipparcos when measuring binary Cepheids like Polaris. The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about the distance. The next major step in high precision parallax measurements comes from ''Gaia'', a space astrometry mission launched in 2013 and intended to measure stellar parallax to within 25 microarcseconds (μas). Although it was originally planned to limit Gaia's observations to stars fainter than magnitude 5.7, tests carried out during the commissioning phase indicated that Gaia could autonomously identify stars as bright as magnitude 3. When Gaia entered regular scientific operations in July 2014, it was configured to routinely process stars in the magnitude range 3 – 20. Beyond that limit, special procedures are used to download raw scanning data for the remaining 230 stars brighter than magnitude 3; methods to reduce and analyse these data are being developed; and it is expected that there will be "complete sky coverage at the bright end" with standard errors of "a few dozen µas".
Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especi ...
does not include a parallax for Polaris, but a distance inferred from it is (445.5 ly) for Polaris B, somewhat further than most previous estimates and several times more accurate. This was further improved to (447.6 ly), upon publication of the Gaia Data Release 3 catalog on 13 June 2022 which superseded Gaia Data Release 2.


Gallery

UrsaMinorCC.jpg, Polaris is the brightest star in the constellation of Ursa Minor (upper right). Ursa Major - Ursa Minor - Polaris.jpg,
Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl" ...
and
Ursa Minor Ursa Minor (Latin: 'Lesser Bear', contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, ...
in relation to Polaris Star Trail above Beccles - geograph.org.uk - 1855505.jpg, A typical Northern Hemisphere star trail with Polaris in the center. Polaris star and companion.jpg, A view of Polaris in a small telescope. Polaris B is separated by 18 arc seconds from the primary star, Polaris A. File:Polaris time-lapse illustrating Cepheid type variability.gif, A 4 day time lapse of Polaris illustrating its Cepheid type variability. Utsjoki.vaakuna.svg, Polaris pictured in the coat of arms of
Utsjoki Utsjoki (; sme, Ohcejohka ; smn, Uccjuuhâ; sms, Uccjokk; no, Utsjok) is a municipality in Finland, the northernmost in the country. It is in Lapland and borders Norway as well as the municipality of Inari. The municipality was founded in 18 ...


See also

*
Extraterrestrial sky In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth. The only extraterrestrial sky that has been directly observed and photographed by astronauts is that of the Moon. The skie ...
(for the pole stars of other celestial bodies) * Polar alignment *
Polaris Australis Sigma Octantis is a solitary star in the Octans constellation that forms the pole star of the southern celestial hemisphere, Southern Hemisphere. Its name is also written as σ Octantis, abbreviated as Sigma Oct or σ Oct, and it is offic ...
* Polaris Flare *
Regiment of the North Pole The Regiment of the North Pole, a medieval outdated astronomy term, is a rule saying how to find the celestial North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hem ...


References

{{Authority control F-type supergiants F-type main-sequence stars Classical Cepheid variables Triple star systems Northern pole stars Ursa Minor (constellation) Ursae Minoris, Alpha Durchmusterung objects Ursae Minoris, 01 008890 011767 0424 Stars with proper names Suspected variables