Polaris: Difference between revisions

Polaris
	Template:Location mark; Location of Polaris (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Ursa Minor
Pronunciation	Template:IPAc-en;; Template:IPAc-en
	α UMi A
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	1.98 (1.86Template:Snd2.13)
	α UMi B
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	8.7
Characteristics
α UMi A
Spectral type	F7Ib + F6V
U−B Template:Engvar	0.38
B−V Template:Engvar	0.60
Variable type	Classical Cepheid
α UMi B
Spectral type	F3V
U−B Template:Engvar	0.01
B−V Template:Engvar	0.42
Variable type	suspected
Astrometry
Radial velocity (Rv)	−17 km/s
Proper motion (μ)	RA: Template:Val mas/yr ; Dec.: Template:Val mas/yr
Parallax (π)	7.54±0.11 mas
Distance	Template:Val ly ; (Template:Val pc)
Absolute magnitude (MV)	−3.6 (α UMi Aa); 3.6 (α UMi Ab); 3.1 (α UMi B)
Orbit
Primary	α UMi Aa
Companion	α UMi Ab
Period (P)	Template:Val yr
Semi-major axis (a)	Template:Val"; (Template:Val)
Eccentricity (e)	Template:Val
Inclination (i)	Template:Val°
Longitude of the node (Ω)	Template:Val°
Periastron epoch (T)	Template:Val
Argument of periastron (ω); (primary)	Template:Val°
Semi-amplitude (K1); (primary)	Template:Val km/s
Details
α UMi Aa
Mass	Template:Val Template:Solar mass
Radius	Template:Val Template:Solar radius
Luminosity (bolometric)	1,260 Template:Solar luminosity
Surface gravity (log g)	2.2 cgs
Temperature	6015 K
Metallicity	112% solar
Rotation	119 days
Rotational velocity (v sin i)	14 km/s
Age	45 - 67? Myr
Metallicity [Fe/H]	{{{metal_fe2}}} dex
α UMi Ab
Mass	1.316 Template:Solar mass
Radius	1.04 Template:Solar radius
Luminosity (bolometric)	3 Template:Solar luminosity
Age	>500? Myr
α UMi B
Mass	1.39 Template:Solar mass
Radius	1.38 Template:Solar radius
Luminosity (bolometric)	3.9 Template:Solar luminosity
Surface gravity (log g)	4.3 cgs
Temperature	6900 K
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Rotational velocity (v sin i)	110 km/s
Age	1.5? Gyr
Other designations
	Template:Odlist
	α UMi A: Template:Odlist
	α UMi B: Template:Odlist
Database references
SIMBAD	α UMi A
	α UMi B

VisualWikitext

Latest revision as of 00:58, 13 November 2025

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Template:Starbox relpos Template:Starbox relpos

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Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinized to Alpha Ursae Minoris) and is commonly called the North Star. 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 stable position of the star in the Northern Sky makes it useful for navigation.^[17]

Although appearing to the naked eye as a single point of light, Polaris is a triple star system, composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is almost certainly^[14] in a wider orbit with Polaris B. The outer companion B was discovered in August 1779 by William Herschel, with the inner Aa/Ab pair only confirmed in the early 20th century.

As the closest Cepheid variable, Polaris Aa's distance is a foundational part of the cosmic distance ladder. The revised Hipparcos stellar parallax gives a distance to Polaris A of about Template:Val (ly) (Template:Val (pc)), while the successor mission Gaia gives a distance of Template:Val (Template:Val) for Polaris B^[9]Template:Efn.

Stellar system

File:Polaris alpha ursae minoris.jpg

Polaris components as seen by the Hubble Space Telescope

Polaris Aa is an evolved yellow supergiant of spectral type F7Ib with 5.4 solar masses (Template:Solar mass). It is the first classical Cepheid to have a mass determined from its orbit. The two smaller companions are Polaris B, a Template:Solar mass F3 main-sequence star orbiting at a distance of Template:Val (AU),^[18] and Polaris Ab (or P), a very close F6 main-sequence star with a mass of Template:Solar mass.^[3] In January 2006, NASA released images, from the Hubble telescope, that showed the three members of the Polaris ternary system.^[19]^[20]

Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a reflecting telescope of his own, one of the best telescopes of the time.^[21]

The variable radial velocity of Polaris A was reported by W. W. Campbell in 1899, which suggested this star is a binary system.^[22] 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 and a large eccentricity of around 0.6.^[23] Moore published preliminary orbital elements of the system in 1929, giving an orbital period of about 29.7 years with an eccentricity of 0.63. This period was confirmed by proper motion studies performed by B. P. Gerasimovič in 1939.^[24]

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.^[25] K. W. Kamper in 1996 produced refined elements with a period of Template:Val and an eccentricity of Template:Val.^[26] In 2019, a study by R. I. Anderson gave a period of Template:Val with an eccentricity of Template:Val.^[10]

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.^[18]^[27]

Observation

Variability

File:AlphaUMiLightCurve.png

A light curve for Polaris, plotted from TESS data^[28]

Polaris Aa, the supergiant primary component, is a low-amplitude population I classical Cepheid variable, although it was once thought to be a type II Cepheid due to its high galactic latitude. Cepheids constitute an important standard candle for determining distance, so Polaris, as the closest such star,^[10] is heavily studied. The variability of Polaris had been suspected since 1852; this variation was confirmed by Ejnar Hertzsprung in 1911.^[29]

The range of brightness of Polaris is given as 1.86–2.13,^[4] 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.^[6]

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 evolution across the Cepheid instability strip, but it may be due to interference between the primary and the first-overtone pulsation modes.^[20]^[30]^[31] 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.^[11]^[31]^[32]

The temperature of Polaris varies by only a small amount during its pulsations, but the amplitude of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than Template:Val to at least Template:Val, may be related to the orbit with Polaris Ab.^[12]

File:Polaris time-lapse illustrating Cepheid type variability.gif

A 4-day time lapse of Polaris illustrating its Cepheid type variability.

Research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, changing from third to second magnitude.^[33] 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 [those] predicted by current theories of stellar evolution".

Torres 2023 published a broad historical compilation of radial velocity and photometric data. He concludes that the change in the Cepheid period has reversed and is now decreasing since roughly 2010. Torres notes that TESS data is of limited utility: as a survey telescope, TESS is optimized for dimmer stars than Polaris, so Polaris significantly over-saturates TESS's cameras. Determining an accurate total brightness for Polaris from TESS is extremely difficult, although it remains suitable for timing the period.^[34]

Furthermore, apparent irregularities in Polaris Aa's behavior may coincide with the periastron passage of Ab, although imprecision in the data prevents a definitive conclusion.^[34] At the Gaia distance, the Aa-Ab closest approach is Template:Val; the radius of the primary supergiant is Template:Solar radius, meaning that the periastron separation is about 29 times its radius. This implies tidal forcing upon Aa's upper atmosphere by Ab. Such binary tidal forcing is known from heartbeat stars, where eccentric periastron approaches cause rich multimode pulsation akin to an electrocardiogram.

Szabados 1992 suggests that, among Cepheids, "phase slips" similar to what happened to Polaris in the mid 1960s are associated with binary systems.^[35]

In 2024, researchers led by Nancy Evans at the Harvard & Smithsonian published a study with fresh data on the inner binary using the interferometric CHARA Array. They improved the solution of the orbit: combining CHARA data with previous Hubble data, and in tandem with the Gaia distance of Template:Val light-years, they confirmed the Cepheid radius estimate of Template:Solar radius and re-determined its mass at Template:Solar mass. The corresponding Polaris Ab mass is Template:Solar mass. Polaris remains overluminous compared to the best Cepheid evolution models, something also seen in V1334 Cygni. Polaris's rapid period change and pulsation amplitude variations are still peculiar compared to other Cepheids, but may be related to the first-overtone pulsations.^[9]

Evans et al also tentatively succeeded in imaging features on the surface of Polaris Aa: large bright and dark patches appear in close-up images, changing over time. Follow up imaging campaigns are required to confirm this detection.^[9] Polaris's age is difficult to model; current best estimates find the Cepheid to be much younger than the two main sequence components, seemingly enough to exclude a common origin, which would be quite unlikely for a triple star system.^[14]^[15]

Torres 2023 and Evans et al 2024 both suggest that recent literature cautiously agree that Polaris is a first overtone pulsator.^[34]^[9]

Role as pole star

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File:Polaris-clock face.jpg

Polaris azimuths vis clock face analogy.^[36]

File:Star Trail above Beccles - geograph.org.uk - 1855505.jpg

A typical Northern Hemisphere star trail with Polaris in the center.

File:Dipper polaris cass.png

Polaris lying halfway between the asterisms Cassiopeia and the Big Dipper.

Because Polaris lies nearly in a direct line with the Earth's rotational axis above the North Pole, it stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. It thus provides a nearly fixed point from which to draw measurements for celestial navigation and for astrometry. The elevation of the star above the horizon gives the approximate latitude of the observer.^[16]

In 2018 Polaris was 0.66° (39.6 arcminutes) away from the pole of rotation (1.4 times the Moon 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, or 27 arcminutes) soon after the year 2100.^[37] 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 rule of thumb. The best approximation^[36] is made using the leading edge of the "Big Dipper" 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.^[38] The celestial pole will move away from α UMi after the 21st century, passing close by Gamma Cephei by about the 41st century, moving towards Deneb by about the 91st century.Template:Fact

The celestial pole was close to Thuban around 2750 BCE,^[38] and during classical antiquity it was slightly closer to Kochab (β UMi) than to Polaris, although still about Template:Val from either star.^[39] It was about the same angular distance from β UMi as to α UMi by the end of late antiquity. The Greek navigator Pytheas 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 (5th century), also termed Λύχνος (Lychnos) akin to a burner or lamp and would reasonably be described as stella polaris from about the High Middle Ages and onwards, both in Greek and Latin. On his first trans-Atlantic voyage in 1492, Christopher Columbus had to correct for the "circle described by the pole star about the pole".^[40] In Shakespeare's play Julius Caesar, written around 1599, Caesar describes himself as being "as constant as the northern star", although in Caesar's time there was no constant northern star. Despite its relative brightness, it is not, as is popularly believed, the brightest star in the sky.^[41]

Polaris was referenced in the classic Nathaniel Bowditch maritime navigation book American Practical Navigator (1802), where it is listed as one of the navigational stars.^[42]

Names

File:Polaris system.jpg

This artist's concept shows: supergiant Polaris Aa, dwarf Polaris Ab, and the distant dwarf companion Polaris B.

The modern name Polaris^[43] is shortened from the Neo-Latin stella polaris ("polar star"), coined in the Renaissance when the star had approached the celestial pole to within a few degrees.^[44]^[45]

Gemma Frisius, 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.^[44]^[45]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[46] 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.^[47]

In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and the entire constellation of Ursa Minor 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").Script error: No such module "Unsubst".

In the "Old English rune poem", the T-rune is apparently associated with "a circumpolar constellation", or the planet Mars.^[48]

In the Hindu Puranas, it became personified under the name Dhruva ("immovable, fixed").^[49]

In the later medieval period, it became associated with the Marian title of Stella Maris "Star of the Sea" (so in Bartholomaeus Anglicus, c. 1270s),^[50] due to an earlier transcription error.^[51]

An older English name, attested since the 14th century, is lodestar "guiding star", cognate with the Old Norse leiðarstjarna, Middle High German leitsterne.^[52]

The ancient name of the constellation Ursa Minor, Cynosura (from the Greek Script error: No such module "Lang". "the dog's tail"),^[53] 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. Script error: No such module "Unsubst".

File:Book of the Fixed Stars Auv0043 ursa minor cropped.jpg

Ursa Minor as depicted in the 964 Persian work Book of Fixed Stars, Polaris named al-Judayy "الجدي" in the lower right.

Its name in traditional pre-Islamic Arab astronomy was al-Judayy الجدي ("the kid", in the sense of a juvenile goat ["le Chevreau"] in Description des Etoiles fixes),^[54] and that name was used in medieval Islamic astronomy as well.^[55]^[56] 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.Template:Fact

It was invoked as a symbol of steadfastness in poetry, as "steadfast star" by Spenser. Shakespeare's sonnet 116 is an example of the symbolism of the north star as a guiding principle: "[Love] is the star to every wandering bark / Whose worth's unknown, although his height be taken."Template:Fact

In Julius Caesar, Shakespeare has Caesar explain his refusal to grant a pardon: "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, but this is only noticeable over centuries.Script error: No such module "Unsubst".

In Inuit astronomy, Polaris is known as Nuutuittuq (syllabics: Script error: No such module "Lang".).^[57]

In traditional Lakota star knowledge, Polaris is named "Wičháȟpi Owáŋžila". This translates to "The Star that Sits Still". This name comes from a Lakota story in which he married Tȟapȟúŋ Šá Wíŋ, "Red Cheeked Woman". However, she fell from the heavens, and in his grief Wičháȟpi Owáŋžila stared down from "waŋkátu" (the above land) forever.^[58]

The Plains Cree call the star in Nehiyawewin: acâhkos êkâ kâ-âhcît "the star that does not move" (syllabics: Script error: No such module "Lang".).^[59]

In Mi'kmawi'simk the star is named Tatapn.^[60]

In the ancient Finnish worldview, the North Star has also been called taivaannapa and naulatähti ("the nailstar") because it seems to be attached to the firmament or even to act as a fastener for the sky when other stars orbit it. Since the starry sky seemed to rotate around it, the firmament is thought of as a wheel, with the star as the pivot on its axis. The names derived from it were sky pin and world pin.Script error: No such module "Unsubst".

Distance

Since Leavitt's discovery of the Cepheid variable period-luminosity relationship, and corresponding utility as a standard candle, the distance to Polaris has been highly sought-after by astronomers. It is the closest Cepheid to Earth, and thus key to calibrating the Cepheid standard candle; Cepheids form the base of the cosmic distance ladder by which to probe the cosmological nature of the universe.^[61]

Distance measurement techniques depend on whether or not components A and B are a physical pair, that is, gravitationally bound. If they are, then their estimated distance can be presumed to be equal.Template:Efn Gravitational binding of this pair is well supported by observations, and the presumption of common distance is widely adopted in historical and recent estimates.^[62]^[63]^[64]^[26]^[65]^[61]^[14]^[9]

For most of the 20th century, available observation technologies remained inadequate to precisely measure absolute parallax.^[66]^[61] Instead, the main technique was to use theoretical models of stellar evolution for both main sequence and giant stars, combined with spectroscopic and photometric data to estimate distances. Such modeling relies on theoretical assumptions and guesses, and contains much systematic error and statistical uncertainties in population data. Even by 2013, these techniques were still struggling to achieve even 10% precision in either main sequence^[67] or Cepheid^[14] modeling.

Further progress was thus limited until the advent of Hipparcos, the first instrument able to engage in all-sky absolute parallax astrometry.^[66] Its first data release was in 1997.

Selected distance estimates to Polaris
Published	Component	Distance		Source	Notes
Published	Component	Template:Nobold	Template:Nobold	Source	Notes
1966	B	(Template:Val)Template:Efn	(Template:Val)Template:Efn	Fernie^[62]	Photometry and modeling of BTemplate:Efn
1977	B	(Template:Val)Template:Efn	(Template:Val)Template:Efn	Turner^[63]	Photometry and modeling of BTemplate:Efn
1978	A	Template:Val^*	Template:Val^*	Gauthier and Fernie^[64]	Modeling extinction and Cepheid evolution of A
1996	B	Template:Val^*	Template:Val^*	Kamper^[26]	Photometry and modeling of B, reproducing prior estimates
1997	A	Template:Val	Template:Val	Hipparcos^[68]	All-sky/absolute^[66] parallax observations, of the primary variableTemplate:Efn
2004-2013	A, B	Template:Val	Template:Val	Turner/Turner et al	Cepheid evolution modeling^[30], cluster kinematics and ZAMS fitting^[30]^[65], photometry and modeling of B^[65], spectral line ratios of A calibrated on yellow supergiants^[61]
		Template:Val	Template:Val
		Template:Val	Template:Val
2007Template:Efn	A	Template:Val	Template:Val	Hipparcos^[2]^[67]	All-sky/absolute parallax observations, revised analysis, of the primary variableTemplate:Efn
2008	B	Template:Val^*	Template:Val^*	Usenko & Klochkova^[7]	Photometry and modeling of B
2014	A	Template:Val	Template:Val	Neilson^[69]	Cepheid evolution modeling, independent of any distance prior
2018	B	Template:Val	Template:Val	Hubble, Bond et al.^[14]	Relative^[66] parallax of the wide component referencing photometrically-calibrated background stars
2018	B	Template:Val	Template:Val	Gaia DR2^[70]	All-sky/absolute^[66] parallax observations, of the wide componentTemplate:Efn
2020	B	Template:Val	Template:Val	Gaia DR3^[5]^[9]	All-sky/absolute parallax observations, of the wide componentTemplate:Efn

<templatestyles src="Citation/styles.css"/>^{^} * This estimate didn't state its uncertainty

After the arrival of the Hipparcos data, the distance to Polaris and consequent analysis of its Cepheid variation was controversial. The Hipparcos distance for Polaris was broadly but not universally adopted.^[20] Immediately, the Hipparcos data for the nearest few hundred Cepheids appeared to clarify Cepheid models and to clear up then-tension in higher rungs of the distance ladder.^[68] However alternatives remained; particularly by Turner et al, who published several papers between 2004 and 2013.^[61]

File:Stellarparallax parsec1.svg

Stellar parallax is the basis for the parsec, which is the distance from the Sun to an astronomical object which has a parallax angle of one arcsecond. (1 AU and 1 pc are not to scale, 1 pc = about 206265 AU)

In 2018, Bond et al^[14] used the Hubble Space Telescope to provide an alternate direct measurement of Polaris's parallax; they summarize the back-and-forth:

However, Turner et al. (2013, hereafter TKUG13)^[61] argue that the parallax of Polaris is considerably larger, 10.10 ± 0.20 mas (d = Template:Val pc). The evidence cited by TKUG13 for this “short” distance includes (1) a photometric parallax for Polaris B based on measured photometry, spectral classification, and main-sequence fitting; (2) a claim that there is a sparse cluster of A-, F-, and G-type stars within 3° of Polaris, with proper motions and radial velocities similar to that of the Cepheid, for which the Hipparcos parallaxes combined with main-sequence fitting give a distance of 99 pc; and (3) a determination of the absolute visual magnitude of Polaris based on line ratios in high-resolution spectra, calibrated against supergiants with well-established luminosities. [...]
[...]
In a critique of the TKUG13 paper, van Leeuwen (2013, hereafter L13)^[67] defended the Hipparcos parallax by presenting details of the solution, concluding that “the Hipparcos data cannot in any way support” the large parallax advocated by TKUG13. Using Hipparcos data, L13 also questioned the reality of the sparse cluster proposed by TKUG13, presenting evidence against it both from the color versus absolute-magnitude diagram for stars within 3° of Polaris, and their non-clustered distribution of proper motions. Lastly, L13 examined the absolute magnitudes of nearly 400 stars of spectral type F3 V in the Hipparcos catalog with parallax errors of less than 10%, and showed that the absolute magnitude of Polaris B would fall well within the observed MV distribution for F3 V stars, based on either the Hipparcos parallax of A or the larger parallax proposed by TKUG13. Thus, he concluded that the photometric parallax of B does not give a useful discriminant.
— Template:Comma separated entries

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Bond et al go on to find a trigonometric parallax (independent of Hipparcos) that implies a distance further-still than the "long" Hipparcos distance, well outside the plausible range of the "short" distance estimates.

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 Template:Val (μas).^[71] 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.^[72] 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".^[73]

Gaia DR2 does not include a parallax for Polaris A, but a distance inferred from Polaris B is Template:Val (Template:Val),^[70] somewhat further than most previous estimates and (in principle) considerably more accurate. There are known to be considerable systematic uncertainties in DR2.^[74]

Gaia DR3 significantly improved both the statistical and systematic uncertainties, although the latter remain numerous and on the order of Template:Val^[75]; the new estimate is Template:Val (Template:Val) using the baseline parallax zeropoint correction.^[5]^[9]Template:Efn

Gaia DR4 (expected December 2026) will further improve the statistical and systematic uncertainties in general, and the data pipelines for variable and multiple stars in particular.^[76] Multistar orbital solutions will become available, greatly aiding the study of Cepheids and Polaris, and in particular, may enable solving the outer AB orbit.^[9]

In popular culture

Polaris is depicted in the flag and coat of arms of the Canadian Inuit territory of Nunavut,^[77] the flag of the U.S. states of Alaska and Minnesota,^[78] and the flag of the U.S. city of Duluth, Minnesota.^[79]^[80]

Vexillology

Flag of Nunavut

Flag of Nunavut
Flag of Alaska

Flag of Alaska
Flag of Minnesota

Flag of Minnesota
Flag of Duluth, Minnesota

Flag of Duluth, Minnesota
Flag of Maine

Flag of Maine
Flag of Maine (1901–1909)

Flag of Maine (1901–1909)
Flag of the Pan-American Exposition (1901)[81]

Flag of the Pan-American Exposition (1901)^[81]
Sledge flag used by Francis Leopold McClintock in the Arctic (1852–1854)[82]

Sledge flag used by Francis Leopold McClintock in the Arctic (1852–1854)^[82]

Heraldry

Coat of arms of Nunavut

Coat of arms of Nunavut
Seal of Minnesota

Seal of Minnesota
Seal of Maine

Seal of Maine
Coat of arms of UtsjokiScript error: No such module "Unsubst".

Coat of arms of UtsjokiScript error: No such module "Unsubst".

Ships

The Chinese spy ship Beijixing is named after Polaris.
USS Polaris is named after Polaris

Gallery

Polaris is the brightest star in the constellation of Ursa Minor (upper right).

Polaris is the brightest star in the constellation of Ursa Minor (upper right).
Big Dipper and Ursa Minor in relation to Polaris

Big Dipper and Ursa Minor in relation to Polaris
A view of Polaris in a small telescope. Polaris B is separated by 18 arc seconds from the primary star, Polaris A.

A view of Polaris in a small telescope. Polaris B is separated by 18 arc seconds from the primary star, Polaris A.
Polaris, its surrounding integrated flux nebula, and NGC188Script error: No such module "Unsubst".

Polaris, its surrounding integrated flux nebula, and NGC188Script error: No such module "Unsubst".

Notes

Template:Notelist

References

Template:Reflist

Template:Sister project

Template:Sky

Template:S-end Template:Pole star Template:Stars of Ursa Minor Template:Portal bar Template:Authority control

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Observation data Epoch J2000 Equinox J2000
Template:Location mark Location of Polaris (circled)
Constellation	Ursa Minor
Pronunciation	Template:IPAc-en; Template:IPAc-en^[1]
α UMi A
Right ascension	Template:RA^[2]
Declination	Template:DEC^[2]
Apparent magnitude (V)	1.98^[3] (1.86Template:Snd2.13)^[4]
α UMi B
Right ascension	Template:RA^[5]
Declination	Template:DEC^[5]
Apparent magnitude (V)	8.7^[3]
Characteristics
α UMi A
Spectral type	F7Ib + F6V^[6]
U−B Template:Engvar	0.38^[3]
B−V Template:Engvar	0.60^[3]
Variable type	Classical Cepheid^[4]
α UMi B
Spectral type	F3V^[3]
U−B Template:Engvar	0.01^[7]
B−V Template:Engvar	0.42^[7]
Variable type	suspected^[4]
Astrometry

Radial velocity (R_v)	−17^[8] km/s
Proper motion (μ)	RA: Template:Val^[2] mas/yr Dec.: Template:Val^[2] mas/yr
Parallax (π)	7.54±0.11 mas^[2]
Distance	Template:Val ly (Template:Val pc)^[9]
Absolute magnitude (M_V)	−3.6 (α UMi Aa)^[3] 3.6 (α UMi Ab)^[3] 3.1 (α UMi B)^[3]

Orbit^[9]
Primary	α UMi Aa
Companion	α UMi Ab
Period (P)	Template:Val yr
Semi-major axis (a)	Template:Val" (Template:Val^[10])
Eccentricity (e)	Template:Val
Inclination (i)	Template:Val°
Longitude of the node (Ω)	Template:Val°
Periastron epoch (T)	Template:Val
Argument of periastron (ω) (primary)	Template:Val°
Semi-amplitude (K₁) (primary)	Template:Val km/s
Details
α UMi Aa
Mass	Template:Val^[9] Template:Solar mass
Radius	Template:Val^[9] Template:Solar radius
Luminosity (bolometric)	1,260^[11] Template:Solar luminosity
Surface gravity (log g)	2.2^[12] cgs
Temperature	6015^[7] K
Metallicity	112% solar^[13]
Rotation	119 days^[6]
Rotational velocity (v sin i)	14^[6] km/s
Age	45 - 67?^[14]^[15] Myr

Metallicity [Fe/H]	{{{metal_fe2}}} dex

α UMi Ab
Mass	1.316^[9] Template:Solar mass
Radius	1.04^[3] Template:Solar radius
Luminosity (bolometric)	3^[3] Template:Solar luminosity
Age	>500?^[15] Myr
α UMi B
Mass	1.39^[3] Template:Solar mass
Radius	1.38^[7] Template:Solar radius
Luminosity (bolometric)	3.9^[7] Template:Solar luminosity
Surface gravity (log g)	4.3^[7] cgs
Temperature	6900^[7] K
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Rotational velocity (v sin i)	110^[7] km/s
Age	1.5?^[14]^[15] Gyr
Other designations
Template:Odlist
α UMi A: Template:Odlist
α UMi B: Template:Odlist
Database references
SIMBAD	α UMi A
	α UMi B

Polaris: Difference between revisions

Latest revision as of 00:58, 13 November 2025

Contents

Stellar system

Observation

Variability

Role as pole star

Names

Distance

In popular culture

Vexillology

Heraldry

Ships

Gallery

See also

Notes

References

Navigation menu

@@ Line 1: / Line 1: @@
-{{short description|Brightest star in the constellation Ursa Minor}}
+{{Short description|Northern pole-star; brightest star in Ursa Minor}}
 {{about|the Earth's current north star|such stars in general|pole star||Polaris (disambiguation)|and|North Star (disambiguation)}}
 {{redirect|Stella Polaris|the military operation|Operation Stella Polaris}}
@@ Line 17: / Line 17: @@
 {{Starbox observe 2s
 | epoch = J2000
-| equinox = <!--Equinox of coordinates (defaults to epoch)-->
 | pronounce = {{IPAc-en|p|ə|'|l|ɛər|ɪ|s|,_|-|ˈ|l|æ|r|-}};<br/>{{IPAc-en|UK|p|ə|'|l|ɑːr|ɪ|s}}<ref>{{cite web |title=Polaris {{pipe}} meaning in the Cambridge English Dictionary |website=[[Cambridge English Dictionary]] |url=https://dictionary.cambridge.org/dictionary/english/polaris |access-date=11 December 2020}}</ref>
 | constell = [[Ursa Minor]]
@@ Line 53: / Line 52: @@
 {{Starbox astrometry
   | radial_v = −17<ref>{{Cite journal |last=Campbell |first=William Wallace |title=The radial velocities of 915 stars |journal=Lick Observatory Bulletin|year=1913 |volume=229 |page=113 |doi=10.5479/ADS/bib/1913LicOB.7.113C |bibcode=1913LicOB...7..113C }}</ref>
-  | prop_mo_ra = {{val|198.8|0.20}}<ref name=hipparcos2/>
+  | prop_mo_ra = {{val|44.48|0.11}}<ref name=hipparcos2/>
-  | prop_mo_dec = {{val|-15|0.30}}<ref name=hipparcos2/>
+  | prop_mo_dec = {{val|-11.85|0.13}}<ref name=hipparcos2/>
   | parallax = 7.54
   | p_error = 0.11
@@ Line 120: / Line 119: @@
 | rotation               =   119 days<ref name=lee>{{Cite journal | last1 = Lee | first1 = B. C. | last2 = Mkrtichian | first2 = D. E. | last3 = Han | first3 = I. | last4 = Park | first4 = M. G. | last5 = Kim | first5 = K. M. | title = Precise Radial Velocities of Polaris: Detection of Amplitude Growth | doi = 10.1088/0004-6256/135/6/2240 | journal = The Astronomical Journal | volume = 135 | issue = 6 | pages = 2240 | year = 2008 |arxiv = 0804.2793 |bibcode = 2008AJ....135.2240L | s2cid = 12176373 }}</ref>
 | rotational_velocity    =   14<ref name=lee/>
-| age_myr                =   45 - 67<ref name=neilson2021>{{cite conference |bibcode=2021ASPC..529...72N |title=The Curious Case of the North Star: The Continuing Tension Between Evolution Models and Measurements of Polaris |last1=Neilson |first1=H. R. |last2=Blinn |first2=H. |conference=RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators |date=2021 |volume=529 |page=72 |arxiv=2003.02326 }}</ref>
+| age_myr                =   45 - 67?<ref name=bond/><ref name=neilson2021>{{cite conference |bibcode=2021ASPC..529...72N |title=The Curious Case of the North Star: The Continuing Tension Between Evolution Models and Measurements of Polaris |last1=Neilson |first1=H. R. |last2=Blinn |first2=H. |conference=RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators |date=2021 |volume=529 |page=72 |arxiv=2003.02326 }}</ref>
 }}
 {{Starbox detail|no_heading=y
@@ Line 128: / Line 127: @@
 | radius                 =   1.04<ref name=hst/>
 | luminosity_bolometric  =   3<ref name=hst/>
-| age_myr                =   >500<ref name=neilson2021/>
+| age_myr                =   >500?<ref name=neilson2021/>
 | component2             =   α UMi B
 | mass2                  =   1.39<ref name=hst/>
@@ Line 136: / Line 135: @@
 | temperature2           =   6900<ref name=usenko/>
 | rotational_velocity2   =   110<ref name=usenko/>
-| age_gyr2               =   1.5<ref name=neilson2021/>
+| age_gyr2               =   1.5?<ref name=bond/><ref name=neilson2021/>
 }}
 {{Starbox catalog
@@ Line 151: / Line 150: @@
 {{starbox end}}
-'''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 [[apparent magnitude]] that fluctuates around 1.98,<ref name=hst/> it is the brightest star in the constellation and is readily visible to the [[naked eye]] at night.<ref name=Kaler>{{cite web |url=http://stars.astro.illinois.edu/sow/polaris.html |title=Polaris (Alpha Ursae Minoris) |first=Jim |last=Kaler |author-link=James B. Kaler |website=Stars |access-date=2020-09-09}}</ref> The position of the star lies less than [[angular distance|1°]] away from the north [[celestial pole]], making it the current northern [[pole star]]. The stable position of the star in the [[northern celestial hemisphere|Northern Sky]] makes it useful for [[celestial navigation|navigation]].<ref name="s936">{{cite web | last=McNamee | first=Gregory | title=How the stars, planets and other celestial objects got their names | website=CNN | date=2021-05-26 | url=https://edition.cnn.com/2021/05/25/world/how-stars-planets-constellations-comets-named-scn/index.html | access-date=2024-08-28}}</ref>
+'''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'''. With an [[apparent magnitude]] that fluctuates around 1.98,<ref name=hst/> it is the brightest star in the constellation and is readily visible to the [[naked eye]] at night.<ref name=Kaler>{{cite web |url=http://stars.astro.illinois.edu/sow/polaris.html |title=Polaris (Alpha Ursae Minoris) |first=Jim |last=Kaler |author-link=James B. Kaler |website=Stars |access-date=2020-09-09}}</ref> The position of the star lies less than [[angular distance|1°]] away from the north [[celestial pole]], making it the current northern [[pole star]]. The stable position of the star in the [[northern celestial hemisphere|Northern Sky]] makes it useful for [[celestial navigation|navigation]].<ref name="s936">{{cite web | last=McNamee | first=Gregory | title=How the stars, planets and other celestial objects got their names | website=CNN | date=2021-05-26 | url=https://edition.cnn.com/2021/05/25/world/how-stars-planets-constellations-comets-named-scn/index.html | access-date=2024-08-28}}</ref>
-As the closest [[Cepheid variable]] its distance is used as part of the [[cosmic distance ladder]]. The revised ''[[Hipparcos]]'' [[stellar parallax]] gives a distance to Polaris of about {{convert|433|ly|pc|abbr=off|lk=on}}, while the successor mission [[Gaia (spacecraft)|''Gaia'']] gives a distance of about {{convert|448|ly|pc|abbr=off|lk=on}}.
+Although appearing to the naked eye as a single point of light, Polaris is a triple [[star system]], composed of the primary, a [[yellow supergiant]] designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is almost certainly<ref name=bond/> in a wider orbit with Polaris B. The outer companion B was discovered in August 1779 by [[William Herschel]], with the inner Aa/Ab pair only confirmed in the early 20th century.
-Although appearing to the naked eye as a single point of light, Polaris is a triple [[star system]], composed of the primary, a [[yellow supergiant]] 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]], where the 'A' refers to what is now known to be the Aa/Ab pair.
+As the closest [[Cepheid variable]], Polaris Aa's distance is a foundational part of the [[cosmic distance ladder]]. The revised ''[[Hipparcos]]'' [[stellar parallax]] gives a distance to Polaris A of about {{val|432|ul=light-years}} (ly) ({{val|133|ul=parsecs}} (pc)), while the successor mission [[Gaia (spacecraft)|''Gaia'']] gives a distance of {{val|446.5|u=ly}} ({{val|136.9|u=pc}}) for Polaris B<ref name=evans2024/>{{efn|If A and B are a physical pair, then they share the same parallax; see [[#Distance]]}}. <!-- These values are converted from mas to pc to ly, with rounding at each step. Using the {{convert}} template here would reverse the rounding and make the conversion mildly inaccurate. -->
 ==Stellar system==
 [[File:Polaris alpha ursae minoris.jpg|thumb|left|upright=1.2|Polaris components as seen by the [[Hubble Space Telescope]]]]
-Polaris Aa is an [[stellar evolution|evolved]] [[yellow supergiant]] of [[stellar classification|spectral type]] F7Ib with 5.4 [[solar mass]]es ({{Solar mass|link=y}}). It is the first classical [[Cepheid]] to have a mass determined from its orbit. The two smaller companions are Polaris B, a {{Solar mass|1.39}} F3 [[main sequence|main-sequence]] star orbiting at a distance of {{val|2400|ul=astronomical units|fmt=commas}} (AU),<ref name=Wielen>{{cite journal|bibcode=2000A&A...360..399W|arxiv = astro-ph/0002406 |title = Polaris: Astrometric orbit, position, and proper motion |journal = Astronomy and Astrophysics |volume = 360 |pages = 399–410 [400–402, 406] |last1 = Wielen |first1 = R. |last2 = Jahreiß |first2 = H. |last3 = Dettbarn |first3 = C. |last4 = Lenhardt |first4 = H. |last5 = Schwan |first5 = H. |year = 2000 }}</ref> and Polaris Ab (or P), a very close F6 main-sequence star with a mass of {{Solar mass|1.26}}.<ref name=hst/> Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a [[reflecting telescope]] of his own,<ref>{{cite book
+Polaris Aa is an [[stellar evolution|evolved]] [[yellow supergiant]] of [[stellar classification|spectral type]] F7Ib with 5.4 [[solar mass]]es ({{Solar mass}}). It is the first classical [[Cepheid]] to have a mass determined from its orbit. The two smaller companions are Polaris B, a {{Solar mass|1.39}} F3 [[main sequence|main-sequence]] star orbiting at a distance of {{val|2400|ul=astronomical units|fmt=commas}} (AU),<ref name=Wielen>{{cite journal|bibcode=2000A&A...360..399W|arxiv = astro-ph/0002406 |title = Polaris: Astrometric orbit, position, and proper motion |journal = Astronomy and Astrophysics |volume = 360 |pages = 399–410 [400–402, 406] |last1 = Wielen |first1 = R. |last2 = Jahreiß |first2 = H. |last3 = Dettbarn |first3 = C. |last4 = Lenhardt |first4 = H. |last5 = Schwan |first5 = H. |year = 2000 }}</ref> and Polaris Ab (or P), a very close F6 main-sequence star with a mass of {{Solar mass|1.26}}.<ref name=hst/> In January 2006, [[NASA]] released images, from the [[Hubble Space Telescope|Hubble telescope]], that showed the three members of the Polaris ternary system.<ref>{{cite web|url=https://hubblesite.org/contents/news-releases/2006/news-2006-02.html |title=There's More to the North Star Than Meets the Eye |publisher=Hubblesite.org |date=2006-01-09 |access-date=2020-02-27}}</ref><ref name=evans/>
+Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a [[reflecting telescope]] of his own, one of the best telescopes of the time.<ref>{{cite book
   | title=An Anthology of Visual Double Stars
   | display-authors=1 | first1=Bob | last1=Argyle
@@ Line 166: / Line 167: @@
   | publisher=Cambridge University Press
   | url=https://books.google.com/books?id=jSmqDwAAQBAJ&pg=PT265
-}}</ref> one of the best telescopes of the time. In January 2006, [[NASA]] released images, from the [[Hubble Space Telescope|Hubble telescope]], that showed the three members of the Polaris ternary system.<ref>{{cite web|url=https://hubblesite.org/contents/news-releases/2006/news-2006-02.html |title=There's More to the North Star Than Meets the Eye |publisher=Hubblesite.org |date=2006-01-09 |access-date=2020-02-27}}</ref><ref name=evans/>
+}}</ref>
 The variable [[radial velocity]] of Polaris A was reported by [[William Wallace Campbell|W. W. Campbell]] in 1899, which suggested this star is a binary system.<ref>{{cite journal
@@ Line 212: / Line 213: @@
 ===Variability===
 [[File:AlphaUMiLightCurve.png|thumb|left|A [[light curve]] for Polaris, plotted from ''[[Transiting Exoplanet Survey Satellite|TESS]]'' data<ref name=MAST>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=8 December 2021}}</ref>]]
-Polaris Aa, the supergiant primary component, is a low-amplitude [[Population I]] [[classical Cepheid variable]], although it was once thought to be a [[type II Cepheid]] due to its high [[galactic latitude]]. Cepheids constitute an important [[standard candle]] for determining distance, so Polaris, as the closest such star,<ref name=Anderson2019/> is heavily studied. The [[Variable star|variability]] of Polaris had been suspected since 1852; this variation was confirmed by [[Ejnar Hertzsprung]] in 1911.<ref>{{cite journal
+Polaris Aa, the supergiant primary component, is a low-amplitude [[population I]] [[classical Cepheid variable]], although it was once thought to be a [[type II Cepheid]] due to its high [[galactic latitude]]. Cepheids constitute an important [[standard candle]] for determining distance, so Polaris, as the closest such star,<ref name=Anderson2019/> is heavily studied. The [[Variable star|variability]] of Polaris had been suspected since 1852; this variation was confirmed by [[Ejnar Hertzsprung]] in 1911.<ref>{{cite journal
   | last1=Hertzsprung | first1=Ejnar
   | title=Nachweis der Veränderlichkeit von α Ursae Minoris
@@ Line 223: / Line 224: @@
 The range of brightness of Polaris is given as 1.86–2.13,<ref name=gcvs/> 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.<ref name=lee/>
-[[File:Integrated Flux Nebula Surrounding Polaris - Kush Chandaria.jpg|thumb|left|Polaris and its surrounding [[Integrated Flux Nebula|integrated flux nebula]]]]
+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 evolution across the Cepheid [[instability strip]], but it may be due to interference between the primary and the first-[[overtone]] pulsation modes.<ref name=evans>{{Cite journal | last1 = Evans | first1 = N. R. | last2 = Sasselov | first2 = D. D. | last3 = Short | first3 = C. I. | doi = 10.1086/338583 | title = Polaris: Amplitude, Period Change, and Companions | journal = The Astrophysical Journal | volume = 567 | issue = 2 | pages = 1121 | year = 2002 |bibcode = 2002ApJ...567.1121E | doi-access = free }}</ref><ref name=turner>{{Cite journal | last1 = Turner | first1 = D. G. | last2 = Savoy | first2 = J. | last3 = Derrah | first3 = J. | last4 = Abdel-Sabour Abdel-Latif | first4 = M. | last5 = Berdnikov | first5 = L. N. | title = The Period Changes of Polaris | doi = 10.1086/427838 | journal = Publications of the Astronomical Society of the Pacific | volume = 117 | issue = 828 | pages = 207 | year = 2005 |bibcode = 2005PASP..117..207T | doi-access = free }}</ref><ref name=neilson>{{Cite journal | last1 = Neilson | first1 = H. R. | last2 = Engle | first2 = S. G. | last3 = Guinan | first3 = E. | last4 = Langer | first4 = N. | last5 = Wasatonic | first5 = R. P. | last6 = Williams | first6 = D. B. | doi = 10.1088/2041-8205/745/2/L32 | title = The Period Change of the Cepheid Polaris Suggests Enhanced Mass Loss | journal = The Astrophysical Journal | volume = 745 | issue = 2 | pages = L32 | year = 2012 |arxiv = 1201.0761 |bibcode = 2012ApJ...745L..32N | s2cid = 118625176 }}</ref> 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.<ref name=fadeyev/><ref name=neilson/><ref name=engle>{{cite journal|doi=10.3847/2515-5172/aad2d0|title=Toward Ending the Polaris Parallax Debate: A Precise Distance to Our Nearest Cepheid from Gaia DR2|journal=Research Notes of the AAS|volume=2|issue=3|pages=126|year=2018|last1=Engle|first1=Scott G|last2=Guinan|first2=Edward F|last3=Harmanec|first3=Petr|bibcode=2018RNAAS...2..126E|s2cid=126329676 |doi-access=free }}</ref>
-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 (a long term change in [[redshift]] that causes light to stretch into longer wavelengths, causing it to appear red) evolution across the Cepheid [[instability strip]], but it may be due to interference between the primary and the first-[[overtone]] pulsation modes.<ref name=evans>{{Cite journal | last1 = Evans | first1 = N. R. | last2 = Sasselov | first2 = D. D. | last3 = Short | first3 = C. I. | doi = 10.1086/338583 | title = Polaris: Amplitude, Period Change, and Companions | journal = The Astrophysical Journal | volume = 567 | issue = 2 | pages = 1121 | year = 2002 |bibcode = 2002ApJ...567.1121E | doi-access = free }}</ref><ref name=turner>{{Cite journal | last1 = Turner | first1 = D. G. | last2 = Savoy | first2 = J. | last3 = Derrah | first3 = J. | last4 = Abdel-Sabour Abdel-Latif | first4 = M. | last5 = Berdnikov | first5 = L. N. | title = The Period Changes of Polaris | doi = 10.1086/427838 | journal = Publications of the Astronomical Society of the Pacific | volume = 117 | issue = 828 | pages = 207 | year = 2005 |bibcode = 2005PASP..117..207T | doi-access = free }}</ref><ref name=neilson>{{Cite journal | last1 = Neilson | first1 = H. R. | last2 = Engle | first2 = S. G. | last3 = Guinan | first3 = E. | last4 = Langer | first4 = N. | last5 = Wasatonic | first5 = R. P. | last6 = Williams | first6 = D. B. | doi = 10.1088/2041-8205/745/2/L32 | title = The Period Change of the Cepheid Polaris Suggests Enhanced Mass Loss | journal = The Astrophysical Journal | volume = 745 | issue = 2 | pages = L32 | year = 2012 |arxiv = 1201.0761 |bibcode = 2012ApJ...745L..32N | s2cid = 118625176 }}</ref> 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.<ref name=fadeyev/><ref name=neilson/><ref name=engle>{{cite journal|doi=10.3847/2515-5172/aad2d0|title=Toward Ending the Polaris Parallax Debate: A Precise Distance to Our Nearest Cepheid from Gaia DR2|journal=Research Notes of the AAS|volume=2|issue=3|pages=126|year=2018|last1=Engle|first1=Scott G|last2=Guinan|first2=Edward F|last3=Harmanec|first3=Petr|bibcode=2018RNAAS...2..126E|s2cid=126329676 |doi-access=free }}</ref>
-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&nbsp;[[kelvin|K]] to at least 170&nbsp;K, may be related to the orbit with Polaris Ab.<ref name=usenko2005/>
+The temperature of Polaris varies by only a small amount during its pulsations, but the amplitude of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than {{val|50|ul=K}} to at least {{val|170|u=K}}, may be related to the orbit with Polaris Ab.<ref name=usenko2005/>
+[[File:Polaris time-lapse illustrating Cepheid type variability.gif|thumb|left|A 4-day time lapse of Polaris illustrating its Cepheid type variability.]]
 Research reported in ''[[Science (journal)|Science]]'' suggests that Polaris is 2.5 times brighter today than when [[Ptolemy]] observed it, changing from third to second magnitude.<ref>{{cite journal|doi=10.1126/science.304.5678.1740b|pmid=15205508|year=2004|last1=Irion|first1=R|title=American Astronomical Society meeting. As inconstant as the Northern Star|journal=Science|volume=304|issue=5678|pages=1740–1|s2cid=129246155}}</ref> 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 [those] predicted by current theories of [[Stellar Evolution|stellar evolution]]".
-In 2024, researchers led by Nancy Evans at the [[Harvard–Smithsonian Center for Astrophysics|Harvard & Smithsonian]], have studied with more accuracy the Polaris' smaller companion orbit using the [[CHARA Array]]. During this observation campaign they have succeeded in shooting Polaris features on its surface; large bright places and dark ones have appeared in close-up images, changing over time. Further, Polaris diameter size has been re-measured to {{solar radius|46}}, using the ''Gaia'' distance of {{val|446|1}} light-years, and its mass was determined at {{solar mass|5.13}}.<ref name=evans2024>{{Cite journal |last1=Evans |first1=Nancy Remage |last2=Schaefer |first2=Gail H. |last3=Gallenne |first3=Alexandre |last4=Torres |first4=Guillermo |last5=Horch |first5=Elliott P. |last6=Anderson |first6=Richard I. |last7=Monnier |first7=John D. |last8=Roettenbacher |first8=Rachael M. |last9=Baron |first9=Fabien |last10=Anugu |first10=Narsireddy |last11=Davidson |first11=James W. |last12=Kervella |first12=Pierre |last13=Bras |first13=Garance |last14=Proffitt |first14=Charles |last15=Mérand |first15=Antoine |date=2024-08-01 |title=The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array |bibcode=2024ApJ...971..190E |journal=The Astrophysical Journal |volume=971 |issue=2 |pages=190 |doi=10.3847/1538-4357/ad5e7a |doi-access=free |arxiv=2407.09641 |issn=0004-637X}}</ref>
+Torres 2023 published a broad historical compilation of radial velocity and photometric data. He concludes that the change in the Cepheid period has reversed and is now decreasing since roughly 2010. Torres notes that [[TESS]] data is of limited utility: as a survey telescope, TESS is optimized for dimmer stars than Polaris, so Polaris significantly over-saturates TESS's cameras. Determining an accurate total brightness for Polaris from TESS is extremely difficult, although it remains suitable for timing the period.<ref name=torres2023>{{cite journal |last1=Torres |first1=Guillermo |title=The spectroscopic orbit of Polaris and its pulsation properties |journal=Monthly Notices of the Royal Astronomical Society |date=2023 |volume=526 |issue=2 |page=2510 |doi=10.1093/mnras/stad2735 |doi-access=free |arxiv=2309.03257 |bibcode=2023MNRAS.526.2510T }}</ref>
+Furthermore, apparent irregularities in Polaris Aa's behavior may coincide with the periastron passage of Ab, although imprecision in the data prevents a definitive conclusion.<ref name=torres2023/> At the Gaia distance, the Aa-Ab closest approach is {{val|6.2|ul=AU}}; the radius of the primary supergiant is {{solar radius|46}}, meaning that the periastron separation is about 29 times its radius. This implies tidal forcing upon Aa's upper atmosphere by Ab. Such binary tidal forcing is known from [[heartbeat stars]], where eccentric periastron approaches cause rich multimode pulsation akin to an [[electrocardiogram]].
+Szabados 1992 suggests that, among Cepheids, "phase slips" similar to what happened to Polaris in the mid 1960s are associated with binary systems.<ref name=szabados1992>{{cite journal |last1=Szabados |first1=L. |title=Effects of Duplicity on the Period Changes of Cepheids |journal=IAU Colloquium 135: Complementary Approaches to Double and Multiple Star Research |date=1992 |volume=32 |page=255 |bibcode=1992ASPC...32..255S }}</ref>
+In 2024, researchers led by Nancy Evans at the [[Harvard–Smithsonian Center for Astrophysics|Harvard & Smithsonian]] published a study with fresh data on the inner binary using the interferometric [[CHARA Array]]. They improved the solution of the orbit: combining CHARA data with previous Hubble data, and in tandem with the ''Gaia'' distance of {{val|446|1}} light-years, they confirmed the Cepheid radius estimate of {{solar radius|46}} and re-determined its mass at {{solar mass|{{val|5.13|0.28}}}}.  The corresponding Polaris Ab mass is {{solar mass|{{val|1.316|0.028}}}}. Polaris remains overluminous compared to the best Cepheid evolution models, something also seen in [[V1334 Cygni]]. Polaris's rapid period change and pulsation amplitude variations are still peculiar compared to other Cepheids, but may be related to the first-overtone pulsations.<ref name=evans2024>{{Cite journal |last1=Evans |first1=Nancy Remage |last2=Schaefer |first2=Gail H. |last3=Gallenne |first3=Alexandre |last4=Torres |first4=Guillermo |last5=Horch |first5=Elliott P. |last6=Anderson |first6=Richard I. |last7=Monnier |first7=John D. |last8=Roettenbacher |first8=Rachael M. |last9=Baron |first9=Fabien |last10=Anugu |first10=Narsireddy |last11=Davidson |first11=James W. |last12=Kervella |first12=Pierre |last13=Bras |first13=Garance |last14=Proffitt |first14=Charles |last15=Mérand |first15=Antoine |date=2024-08-01 |title=The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array |bibcode=2024ApJ...971..190E |journal=The Astrophysical Journal |volume=971 |issue=2 |pages=190 |doi=10.3847/1538-4357/ad5e7a |doi-access=free |arxiv=2407.09641 |issn=0004-637X}}</ref>
+Evans et al also tentatively succeeded in imaging features on the surface of Polaris Aa: large bright and dark patches appear in close-up images, changing over time. Follow up imaging campaigns are required to confirm this detection.<ref name=evans2024/>  Polaris's age is difficult to model; current best estimates find the Cepheid to be much younger than the two main sequence components, seemingly enough to exclude a common origin, which would be quite unlikely for a triple star system.<ref name=bond/><ref name=neilson2021/>
+Torres 2023 and Evans et al 2024 both suggest that recent literature cautiously agree that Polaris is a first overtone pulsator.<ref name=torres2023/><ref name=evans2024/>
 ===Role as pole star===
 {{main|Pole star}}
-[[File:Polaris-clock face.jpg|thumb|left|Polaris azimuths vis clock face analogy.<ref name="kaizad_co_uk">{{cite web | url=http://www.kaizad.co.uk/data/Nav/Polaris.xls | title=A visual method to correct a ship's compass using Polaris using Ursa Major as a point of reference | access-date=2016-08-07 | archive-date=2010-08-27 | archive-url=https://web.archive.org/web/20100827042213/http://www.kaizad.co.uk/data/Nav/Polaris.xls | url-status=dead }}</ref>]]
+[[File:Polaris-clock face.jpg|thumb|left|upright|Polaris azimuths vis clock face analogy.<ref name="kaizad_co_uk">{{cite web | url=http://www.kaizad.co.uk/data/Nav/Polaris.xls | title=A visual method to correct a ship's compass using Polaris using Ursa Major as a point of reference | access-date=2016-08-07 | archive-date=2010-08-27 | archive-url=https://web.archive.org/web/20100827042213/http://www.kaizad.co.uk/data/Nav/Polaris.xls | url-status=dead }}</ref>]]
 [[File:Star Trail above Beccles - geograph.org.uk - 1855505.jpg|thumb|A typical Northern Hemisphere [[star trail]] with Polaris in the center.]]
 [[File:Dipper polaris cass.png|thumb|Polaris lying halfway between the [[Asterism (astronomy)|asterisms]] [[Cassiopeia (constellation)|Cassiopeia]] and the [[Big Dipper]].]]
@@ Line 307: / Line 318: @@
 ==Distance==
-[[Image:Stellarparallax parsec1.svg|thumb|right|Stellar parallax is the basis for the [[parsec]], which is the distance from the [[Sun]] to an [[astronomical object]] which has a [[parallax]] angle of one [[arcsecond]]. (1 [[astronomical unit|AU]] and 1 [[Parsec|pc]] are not to scale, 1 pc = about 206265 AU)]]
+Since [[Henrietta Swan Leavitt|Leavitt]]'s discovery of the [[Cepheid variable]] period-luminosity relationship, and corresponding utility as a [[standard candle]], the distance to Polaris has been highly sought-after by astronomers. It is the closest Cepheid to Earth, and thus key to calibrating the Cepheid standard candle; Cepheids form the base of the [[cosmic distance ladder]] by which to probe the cosmological nature of the universe.<ref name="turner2012" />
-Many recent papers calculate the distance to Polaris at about 433 [[light-years]] (133 parsecs),<ref name="evans" /> based on parallax measurements from the [[Hipparcos]] 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).<ref name="turner2012">{{cite journal|bibcode=2013ApJ...762L...8T|title=The Pulsation Mode of the Cepheid Polaris|journal=The Astrophysical Journal Letters|volume=762|issue=1|pages=L8|last1=Turner|first1=D. G.|last2=Kovtyukh|first2=V. V.|last3=Usenko|first3=I. A.|last4=Gorlova|first4=N. I.|date=2013|doi=10.1088/2041-8205/762/1/L8|arxiv = 1211.6103 |s2cid=119245441}}</ref> Polaris is the closest [[Cepheid variable]] to Earth so its physical parameters are of critical importance to the whole [[cosmic distance ladder|astronomical distance scale]].<ref name="turner2012" /> It is also the only one with a dynamically measured mass.
+Distance measurement techniques depend on whether or not components A and B are a physical pair, that is, [[Binary star|gravitationally bound]]. If they are, then their estimated distance can be presumed to be equal.{{efn|Their minimum spatial separation is the angular separation: 0.09 [[Milliradian|mrad]] (18.2 arcseconds), i.e. 0.009% of their distance from Earth; it could be higher (2x-5x) depending on the orbital eccentricity and orientation of the [[apsides]] to Earth's sightline. In any case, distance estimate uncertainties have far exceeded 0.2%, with only Gaia approaching the latter precision, when neglecting systematic uncertainties.<ref name=Khan2023B/> Future Gaia data may enable solving this outer orbit, constraining the [[apsides]] and thus precisely determining the distance between the components.}} Gravitational binding of this pair is well supported by observations, and the presumption of common distance is widely adopted in historical and recent estimates.<ref name=Fernie1966/><ref name=Turner1977/><ref name=GauthierFernie1978/><ref name=Kamper1996/><ref name=Turner2005/><ref name=turner2012/><ref name=bond/><ref name=evans2024/>
+For [[Stellar_parallax#19th_and_20th_centuries|most of the 20th century]], available observation technologies remained inadequate to precisely measure absolute parallax.<ref name=Brown2021/><ref name=turner2012/> Instead, the main technique was to use theoretical models of [[stellar evolution]] for both [[main sequence fitting|main sequence]] and [[giant stars]], combined with [[spectroscopic]] and [[Photometry (astronomy)|photometric]] data to estimate distances. Such modeling relies on theoretical assumptions and guesses, and contains much [[systematic error]] and statistical uncertainties in population data. Even by 2013, these techniques were still struggling to achieve even 10% precision in either main sequence<ref name=vanLeeuwen2013>{{cite journal |last1=Van Leeuwen |first1=F. |title=The HIPPARCOS parallax for Polaris |journal=Astronomy and Astrophysics |date=2013 |volume=550 |pages=L3 |doi=10.1051/0004-6361/201220871 |arxiv=1301.0890 |bibcode=2013A&A...550L...3V }}</ref> or Cepheid<ref name=bond/> modeling.
+Further progress was thus limited until the advent of [[Hipparcos]], the first instrument able to engage in all-sky absolute parallax astrometry.<ref name=Brown2021/> Its first data release was in 1997.
 {| class="wikitable plainrowheaders" style="margin-right: 0; margin-left: 1em; text-align: center;"
 |+ Selected distance estimates to Polaris
-! scope="col" | Year
+<!-- Beware rounding, these table values are (relatively) carefully rounded from whatever source unit was given -->
-! scope="col" | Component
+! scope="col" rowspan="2" | Published
-! scope="col" | Distance, [[light-year|ly]] ([[parsec|pc]])
+! scope="col" rowspan="2" | Component
-! scope="col" | Notes
+! scope="col" colspan="2" | Distance
+! scope="col" rowspan="2" | Source
+! scope="col" rowspan="2" | Notes
 |-
-! scope="row" | 2006
+! scope="col" | {{nobold|[[Lightyears|ly]]}}
+! scope="col" | {{nobold|[[Parsecs|pc]]}}
+|-
+! scope="row" | 1966
+| B
+| ({{val|359}}){{efn|name=table1966|The paper only estimates an absolute magnitude of roughly 3.3 with an apparent magnitude of 8.51. That implies a [[distance modulus]] of 5.21, implying a distance around 110 pc. A notional magnitude error of ±0.3 would correspond to roughly ±16 pc error.}}
+| ({{val|110}}){{efn|name=table1966}}
+| Fernie<ref name=Fernie1966>{{cite journal |last1=Fernie |first1=J. D. |title=Classical Cepheids with companions. II. Polaris.|journal=Astronomical Journal |date=1966 |volume=71 |page=732 |doi=10.1086/110179 |bibcode=1966AJ.....71..732F}}</ref>
+| Photometry and modeling of B{{efn|name=table1966}}
+|-
+! scope="row" | 1977
+| B
+| ({{val|399}}){{efn|name=table1977}}
+| ({{val|122}}){{efn|name=table1977}}
+| Turner<ref name=Turner1977>{{cite journal |last1=Turner |first1=D. G. |title=A Note on the Reddening of Polaris B |journal=Publications of the Astronomical Society of the Pacific |date=1977 |volume=89 |page=550 |doi=10.1086/130161 |bibcode=1977PASP...89..550T }}</ref>
+| Photometry and modeling of B{{efn|name=table1977|The paper only estimates an absolute magnitude of roughly 3.16. Taken with the quoted apparent magnitude 8.6, that implies a [[distance modulus]] of 5.44, implying a distance around 122 pc. A notional magnitude error of ±0.1 would correspond to roughly ±6 pc error. Extinction was concluded to be negligible.}}
+|-
+! scope="row" | 1978
 | A
-| 330 ly (101 pc)
+| {{val|356}}{{ref|nostddev|*|*}}
-| Turner<ref name=turner/>
+| {{val|109}}{{ref|nostddev|*|*}}
+| Gauthier and Fernie<ref name=GauthierFernie1978>{{cite journal |last1=Gauthier |first1=R. P. |last2=Fernie |first2=J. D. |title=The reddening of Polaris |journal=Publications of the Astronomical Society of the Pacific |date=1978 |volume=90 |page=739 |doi=10.1086/130422 |bibcode=1978PASP...90..739G }}</ref>
+| Modeling extinction and Cepheid evolution of A
+|-
+! scope="row" | 1996
+| B
+| {{val|359}}{{ref|nostddev|*|*}}
+| {{val|110}}{{ref|nostddev|*|*}}
+| Kamper<ref name=Kamper1996/>
+| Photometry and modeling of B, reproducing prior estimates
 |-
-! scope="row" | 2007{{ref label|2007|A|A}}
+! scope="row" | 1997
 | A
-| 433 ly (133 pc)
+| {{val|431|29}}
-| Hipparcos<ref name=hipparcos2/>
+| {{val|132|9}}
+| [[Hipparcos]]<ref name=FeastCatchpole1997>{{cite journal |last1=Feast |first1=M. W. |last2=Catchpole |first2=R. M. |title=The Cepheid period-luminosity zero-point from HIPPARCOS trigonometrical parallaxes |journal=Monthly Notices of the Royal Astronomical Society |date=1997 |volume=286 |issue=1 |pages=L1–L5 |doi=10.1093/mnras/286.1.L1 |doi-access=free |bibcode=1997MNRAS.286L...1F }}</ref>
+| All-sky/absolute<ref name=Brown2021>{{cite journal |last1=Brown |first1=Anthony G. A. |title=Microarcsecond Astrometry: Science Highlights from Gaia |journal=Annual Review of Astronomy and Astrophysics |date=2021 |volume=59 |page=59 |doi=10.1146/annurev-astro-112320-035628 |arxiv=2102.11712 |bibcode=2021ARA&A..59...59B }}</ref> parallax observations, of the primary variable{{efn|name=table1997|Parallax {{val|7.56|0.48|u=mas}}}}
+|-
+! scope="row" rowspan=3 | 2004-2013
+| rowspan=3 | A, B
+| {{val|307|13}}
+| {{val|94|4}}
+| rowspan=3 | Turner/Turner et al
+| rowspan=3 | Cepheid evolution modeling<ref name=turner/>, cluster kinematics and [[ZAMS]] fitting<ref name=turner/><ref name=Turner2005>{{cite journal |last1=Turner |first1=D. G. |title=Is Polaris Leaving the Cepheid Instability Strip? |journal=Odessa Astronomical Publications |date=2005 |volume=18 |page=115 |bibcode=2005OAP....18..115T }}</ref>, photometry and modeling of B<ref name=Turner2005/>, [[spectral line ratios]] of A calibrated on yellow supergiants<ref name=turner2012/>
+|-
+| {{val|329|10}}
+| {{val|101|3}}
+|-
+| {{val|323|7}}
+| {{val|99|2}}
+|-
+! scope="row" | 2007{{efn|name=table2007}}
+| A
+| {{val|432|6}}
+| {{val|133|2}}
+| Hipparcos<ref name=hipparcos2>{{Cite journal | last1 = Van Leeuwen | first1 = F. | title = Validation of the new Hipparcos reduction | doi = 10.1051/0004-6361:20078357 | journal = Astronomy and Astrophysics | volume = 474 | issue = 2 | pages = 653–664 | year = 2007 |arxiv = 0708.1752 |bibcode = 2007A&A...474..653V | s2cid = 18759600 }}</ref><ref name=vanLeeuwen2013/>
+| All-sky/absolute parallax observations, revised analysis, of the primary variable{{efn|name=table2007|Parallax {{val|7.54|0.11|u=mas}}; observations from 1989 to 1993, first analysis published 1997, revised analysis published 2007.}}
 |-
 ! scope="row" | 2008
 | B
-| 359 ly (110 pc)
+| {{val|357}}{{ref|nostddev|*|*}}
+| {{val|109.5}}{{ref|nostddev|*|*}}
 | Usenko & Klochkova<ref name=usenko/>
-|-
+| Photometry and modeling of B
-! scope="row" | 2013
-| B
-| 323 ly (99 pc)
-| Turner, et al.<ref name=turner2012/>
 |-
 ! scope="row" | 2014
 | A
-| ≥ 385 ly (≥ 118 pc)
+| {{val|385|p=> }}
+| {{val|118|p=> }}
 | Neilson<ref name=neilson2>{{cite journal|bibcode=2014A&A...563A..48N|title=Revisiting the fundamental properties of the Cepheid Polaris using detailed stellar evolution models|journal=Astronomy & Astrophysics|volume=563|pages=A48|last1=Neilson|first1=H. R.|date=2014|doi=10.1051/0004-6361/201423482|arxiv = 1402.1177 |s2cid=119252434}}</ref>
+| Cepheid evolution modeling, independent of any distance [[prior probability|prior]]
 |-
 ! scope="row" | 2018
 | B
-| 521 ly (160pc)
+| {{val|521|20}}
-| Bond et al.<ref name=bond>{{cite journal|bibcode=2018ApJ...853...55B|title=Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid|journal=The Astrophysical Journal|volume=853|issue=1|pages=55|last1=Bond|first1=Howard E|last2=Nelan|first2=Edmund P|last3=Remage Evans|first3=Nancy|last4=Schaefer|first4=Gail H|last5=Harmer|first5=Dianne|year=2018|arxiv=1712.08139|doi=10.3847/1538-4357/aaa3f9|s2cid=118875464 |doi-access=free }}</ref>
+| {{val|160|6}}
+| [[Hubble]], Bond et al.<ref name=bond>{{cite journal|bibcode=2018ApJ...853...55B|title=Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid|journal=The Astrophysical Journal|volume=853|issue=1|pages=55|last1=Bond|first1=Howard E|last2=Nelan|first2=Edmund P|last3=Remage Evans|first3=Nancy|last4=Schaefer|first4=Gail H|last5=Harmer|first5=Dianne|year=2018|arxiv=1712.08139|doi=10.3847/1538-4357/aaa3f9|s2cid=118875464 |doi-access=free }}</ref>
+| Relative<ref name=Brown2021/> parallax of the wide component referencing photometrically-calibrated background stars
 |-
 ! scope="row" | 2018
 | B
-| 445.3 ly (136.6 pc){{ref label|2018|B|B}}
+| {{val|445.3|1.7}}
-| Gaia DR2<ref name=bailer-jones/>
+| {{val|136.6|0.5}}
+| [[Gaia]] DR2<ref name=bailer-jones/>
+| All-sky/absolute<ref name=Brown2021/> parallax observations, of the wide component{{efn|name=table2018|Statistical distance calculated using a weak distance prior}}
 |-
 ! scope="row" | 2020
 | B
-| 447.6 ly (137.2pc)
+| {{val|446.5|1.1}}
-| Gaia DR3<ref name="Gaia_DR3"/>
+| {{val|136.9|0.3}}
+| Gaia DR3<ref name="Gaia_DR3"/><ref name=evans2024/>
+| All-sky/absolute parallax observations, of the wide component{{efn|name=table2020|The raw parallax is {{val|7.2869|0.0178|u=mas}}; applying a basic systematic<ref name=Khan2023B/> correction<ref name=LindegrenEA2021>{{cite journal |last1=Lindegren |first1=L. |last2=Bastian |first2=U. |last3=Biermann |first3=M. |last4=Bombrun |first4=A. |last5=De Torres |first5=A. |last6=Gerlach |first6=E. |last7=Geyer |first7=R. |last8=Hernández |first8=J. |last9=Hilger |first9=T. |last10=Hobbs |first10=D. |last11=Klioner |first11=S. A. |last12=Lammers |first12=U. |last13=McMillan |first13=P. J. |last14=Ramos-Lerate |first14=M. |last15=Steidelmüller |first15=H. |last16=Stephenson |first16=C. A. |last17=Van Leeuwen |first17=F. |title=Gaia Early Data Release 3. Parallax bias versus magnitude, colour, and position |journal=Astronomy and Astrophysics |date=2021 |volume=649 |doi=10.1051/0004-6361/202039653 |arxiv=2012.01742 |bibcode=2021A&A...649A...4L }}</ref> gives {{val|7.3045|0.0178|u=mas}}}}
 |}
 {| style="margin-right: 0; margin-left: 1em;"
+|-
+| {{note label|nostddev|*|none}}<nowiki>*</nowiki> This estimate didn't state its uncertainty
 |-
-|{{note label|2007|A|A}} New revision of observations from 1989 to 1993, first published in 1997
-|-
-|{{note label|2018|B|B}} Statistical distance calculated using a weak distance prior
 |}
-The ''Hipparcos'' spacecraft used [[stellar parallax]] to take measurements from 1989 and 1993 with the accuracy of 0.97&nbsp;[[Minute of arc|milliarcsecond]]s  (970 microarcseconds), and it obtained accurate measurements for stellar distances up to 1,000&nbsp;pc away.<ref name=hipparcos>{{Cite journal | doi = 10.1023/A:1005081918325| year = 1997| last1 = Van Leeuwen | first1 = F. | journal = Space Science Reviews| volume = 81| issue = 3/4| pages = 201–409| title = The Hipparcos Mission|bibcode = 1997SSRv...81..201V | s2cid = 189785021}}</ref> The Hipparcos data was examined again with more advanced error correction and statistical techniques.<ref name=hipparcos2>{{Cite journal | last1 = Van Leeuwen | first1 = F. | title = Validation of the new Hipparcos reduction | doi = 10.1051/0004-6361:20078357 | journal = Astronomy and Astrophysics | volume = 474 | issue = 2 | pages = 653–664 | year = 2007 |arxiv = 0708.1752 |bibcode = 2007A&A...474..653V | s2cid = 18759600 }}</ref> Despite the advantages of Hipparcos [[astrometry]], 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.<ref name=turner2012/> The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about the distance.<ref name=polaris-hipparcos>{{cite journal|bibcode=2013A&A...550L...3V|title=The HIPPARCOS parallax for Polaris|journal=Astronomy & Astrophysics|volume=550|pages=L3|last1=Van Leeuwen|first1=F.|date=2013|doi=10.1051/0004-6361/201220871|arxiv = 1301.0890 |s2cid=119284268}}</ref>
+After the arrival of the Hipparcos data, the distance to Polaris and consequent analysis of its Cepheid variation was controversial. The Hipparcos distance for Polaris was broadly but not universally adopted.<ref name="evans" /> Immediately, the Hipparcos data for the nearest few hundred Cepheids appeared to clarify Cepheid models and to clear up then-tension in higher rungs of the distance ladder.<ref name=FeastCatchpole1997/> However alternatives remained; particularly by Turner et al, who published several papers between 2004 and 2013.<ref name="turner2012">{{cite journal|bibcode=2013ApJ...762L...8T|title=The Pulsation Mode of the Cepheid Polaris|journal=The Astrophysical Journal Letters|volume=762|issue=1|pages=L8|last1=Turner|first1=D. G.|last2=Kovtyukh|first2=V. V.|last3=Usenko|first3=I. A.|last4=Gorlova|first4=N. I.|date=2013|doi=10.1088/2041-8205/762/1/L8|arxiv = 1211.6103 |s2cid=119245441}}</ref>
+[[Image:Stellarparallax parsec1.svg|thumb|right|Stellar parallax is the basis for the [[parsec]], which is the distance from the [[Sun]] to an [[astronomical object]] which has a [[parallax]] angle of one [[arcsecond]]. (1 [[astronomical unit|AU]] and 1 [[Parsec|pc]] are not to scale, 1 pc = about 206265 AU)]]
+In 2018, Bond et al<ref name=bond/> used the [[Hubble Space Telescope]] to provide an alternate direct measurement of Polaris's parallax; they summarize the back-and-forth:
+{{Blockquote
+|source=<ref name=bond/>
+|text=
+However, Turner et al. (2013, hereafter TKUG13)<ref name=turner2012/> argue that the parallax of Polaris is considerably larger, 10.10 ± 0.20 mas (d = {{val|99|2}} pc). The evidence cited by TKUG13 for this “short” distance includes (1) a photometric parallax for Polaris B based on measured photometry, spectral classification, and main-sequence fitting; (2) a claim that there is a sparse cluster of A-, F-, and G-type stars within 3° of Polaris, with proper motions and radial velocities similar to that of the Cepheid, for which the Hipparcos parallaxes combined with main-sequence fitting give a distance of 99 pc; and (3) a determination of the absolute visual magnitude of Polaris based on line ratios in high-resolution spectra, calibrated against supergiants with well-established luminosities. [...]
+[...]
+In a critique of the TKUG13 paper, van Leeuwen (2013, hereafter L13)<ref name=vanLeeuwen2013/> defended the Hipparcos parallax by presenting details of the solution, concluding that “the Hipparcos data cannot in any way support” the large parallax advocated by TKUG13. Using Hipparcos data, L13 also questioned the reality of the sparse cluster proposed by TKUG13, presenting evidence against it both from the color versus absolute-magnitude diagram for stars within 3° of Polaris, and their non-clustered distribution of proper motions. Lastly, L13 examined the absolute magnitudes of nearly 400 stars of spectral type F3 V in the Hipparcos catalog with parallax errors of less than 10%, and showed that the absolute magnitude of Polaris B would fall well within the observed MV distribution for F3 V stars, based on either the Hipparcos parallax of A or the larger parallax proposed by TKUG13. Thus, he concluded that the photometric parallax of B does not give a useful discriminant.
+}}
+Bond et al go on to find a trigonometric parallax (independent of Hipparcos) that implies a distance further-still than the "long" Hipparcos distance, well outside the plausible range of the "short" distance estimates.
+The next major step in high precision parallax measurements comes from [[Gaia (spacecraft)|''Gaia'']], a space astrometry mission launched in 2013 and intended to measure stellar parallax to within {{val|25|ul=microarcsecond{{!}}microarcseconds}} (μas).<ref name=gaia>{{cite journal|bibcode=2012MNRAS.426.2463L|title=The expected performance of stellar parametrization with Gaia spectrophotometry|journal=Monthly Notices of the Royal Astronomical Society|volume=426|issue=3|pages=2463|last1=Liu|first1=C.|display-authors=4|last2=Bailer-Jones|first2=C. A. L.|last3=Sordo|first3=R.|last4=Vallenari|first4=A.|last5=Borrachero|first5=R.|last6=Luri|first6=X.|last7=Sartoretti|first7=P.|date=2012|doi=10.1111/j.1365-2966.2012.21797.x|doi-access=free |arxiv = 1207.6005 |s2cid=1841271}}</ref> 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.<ref>{{cite journal |bibcode=2014SPIE.9143E..0YM |title=Enabling Gaia observations of naked-eye stars |last1=Martín-Fleitas |first1=J. |last2=Sahlmann |first2=J. |last3=Mora |first3=A. |last4=Kohley |first4=R. |last5=Massart |first5=B. |last6=l'Hermitte |first6=J. |last7=Le Roy |first7=M. |last8=Paulet |first8=P. |editor-first1=Jacobus M |editor-first2=Mark |editor-first3=Giovanni G |editor-first4=Howard A |editor-last1=Oschmann |editor-last2=Clampin |editor-last3=Fazio |editor-last4=MacEwen |journal=Space Telescopes and Instrumentation 2014: Optical |series=Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave |year=2014 |volume=9143 |pages=91430Y |doi=10.1117/12.2056325 |arxiv=1408.3039 |s2cid=119112009 }}</ref> 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".<ref>{{ Citation | author = T. Prusti | collaboration = GAIA Collaboration | date = 2016 | title = The ''Gaia'' mission | type = forthcoming article | journal = Astronomy and Astrophysics | volume = 595 | pages = A1 | doi = 10.1051/0004-6361/201629272 | arxiv = 1609.04153 | bibcode = 2016A&A...595A...1G | s2cid = 9271090 }}</ref>
+[[Gaia DR2]] does not include a parallax for Polaris A, but a distance inferred from Polaris B is {{val|136.6|0.5|ul=pc}} ({{val|445.5|1.7|ul=ly}}),<ref name=bailer-jones>{{cite journal|bibcode=2018AJ....156...58B|title=Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2|journal=The Astronomical Journal|volume=156|issue=2|pages=58|last1=Bailer-Jones|first1=C. A. L|last2=Rybizki|first2=J|last3=Fouesneau|first3=M|last4=Mantelet|first4=G|last5=Andrae|first5=R|year=2018|doi=10.3847/1538-3881/aacb21|arxiv=1804.10121|s2cid=119289017 |doi-access=free }}</ref> somewhat further than most previous estimates and (in principle) considerably more accurate. There are known to be considerable systematic uncertainties in DR2.<ref name=Khan2019>{{cite journal |last1=Khan |first1=S. |last2=Miglio |first2=A. |last3=Mosser |first3=B. |last4=Arenou |first4=F. |last5=Belkacem |first5=K. |last6=Brown |first6=A. G. A. |last7=Katz |first7=D. |last8=Casagrande |first8=L. |last9=Chaplin |first9=W. J. |last10=Davies |first10=G. R. |last11=Rendle |first11=B. M. |last12=Rodrigues |first12=T. S. |last13=Bossini |first13=D. |last14=Cantat-Gaudin |first14=T. |last15=Elsworth |first15=Y. P. |last16=Girardi |first16=L. |last17=North |first17=T. S. H. |last18=Vallenari |first18=A. |title=New light on the Gaia DR2 parallax zero-point: Influence of the asteroseismic approach, in and beyond the Kepler field |journal=Astronomy and Astrophysics |date=2019 |volume=628 |pages=A35 |doi=10.1051/0004-6361/201935304 |arxiv=1904.05676 |bibcode=2019A&A...628A..35K }}</ref>
+[[Gaia DR3]] significantly improved both the statistical and systematic uncertainties, although the latter remain numerous and on the order of {{val|10|-|60|u=μas}}<ref name=Khan2023B>{{cite journal |last1=Khan |first1=S. |last2=Anderson |first2=R. I. |last3=Miglio |first3=A. |last4=Mosser |first4=B. |last5=Elsworth |first5=Y. P. |title=Investigating Gaia EDR3 parallax systematics using asteroseismology of cool giant stars observed by Kepler, K2, and TESS. II. Deciphering Gaia parallax systematics using red clump stars |journal=Astronomy and Astrophysics |date=2023 |volume=680 |pages=A105 |doi=10.1051/0004-6361/202347919 |arxiv=2310.03654 |bibcode=2023A&A...680A.105K }}</ref>; the new estimate is {{val|136.9|0.3|ul=pc}} ({{val|446.5|1.1|ul=ly}}) using the baseline parallax zeropoint correction.<ref name="Gaia_DR3">{{cite Gaia DR3|576402619921510144}}</ref><ref name=evans2024/>{{efn|name=table2020}}
-The next major step in high precision parallax measurements comes from [[Gaia (spacecraft)|''Gaia'']], a space astrometry mission launched in 2013 and intended to measure stellar parallax to within 25&nbsp;microarcseconds (μas).<ref name=gaia>{{cite journal|bibcode=2012MNRAS.426.2463L|title=The expected performance of stellar parametrization with Gaia spectrophotometry|journal=Monthly Notices of the Royal Astronomical Society|volume=426|issue=3|pages=2463|last1=Liu|first1=C.|display-authors=4|last2=Bailer-Jones|first2=C. A. L.|last3=Sordo|first3=R.|last4=Vallenari|first4=A.|last5=Borrachero|first5=R.|last6=Luri|first6=X.|last7=Sartoretti|first7=P.|date=2012|doi=10.1111/j.1365-2966.2012.21797.x|doi-access=free |arxiv = 1207.6005 |s2cid=1841271}}</ref> 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.<ref>{{cite journal |bibcode=2014SPIE.9143E..0YM |title=Enabling Gaia observations of naked-eye stars |last1=Martín-Fleitas |first1=J. |last2=Sahlmann |first2=J. |last3=Mora |first3=A. |last4=Kohley |first4=R. |last5=Massart |first5=B. |last6=l'Hermitte |first6=J. |last7=Le Roy |first7=M. |last8=Paulet |first8=P. |editor-first1=Jacobus M |editor-first2=Mark |editor-first3=Giovanni G |editor-first4=Howard A |editor-last1=Oschmann |editor-last2=Clampin |editor-last3=Fazio |editor-last4=MacEwen |journal=Space Telescopes and Instrumentation 2014: Optical |series=Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave |year=2014 |volume=9143 |pages=91430Y |doi=10.1117/12.2056325 |arxiv=1408.3039 |s2cid=119112009 }}</ref> 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".<ref>{{ Citation | author = T. Prusti | collaboration = GAIA Collaboration | date = 2016 | title = The ''Gaia'' mission | type = forthcoming article | journal = Astronomy and Astrophysics | volume = 595 | pages = A1 | doi = 10.1051/0004-6361/201629272 | arxiv = 1609.04153 | bibcode = 2016A&A...595A...1G | s2cid = 9271090 }}</ref> [[Gaia Data Release 2]] does not include a parallax for Polaris, but a distance inferred from it is {{val|136.6|0.5|ul=pc}} (445.5 ly) for Polaris B,<ref name=bailer-jones>{{cite journal|bibcode=2018AJ....156...58B|title=Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2|journal=The Astronomical Journal|volume=156|issue=2|pages=58|last1=Bailer-Jones|first1=C. A. L|last2=Rybizki|first2=J|last3=Fouesneau|first3=M|last4=Mantelet|first4=G|last5=Andrae|first5=R|year=2018|doi=10.3847/1538-3881/aacb21|arxiv=1804.10121|s2cid=119289017 |doi-access=free }}</ref> somewhat further than most previous estimates and several times more accurate. This was further improved to {{val|137.2|0.3|ul=pc}} (447.6 ly), upon publication of the [[Gaia Data Release 3]] catalog on 13 June 2022 which superseded Gaia Data Release 2.<ref name="Gaia_DR3">{{cite Gaia DR3|576402619921510144}}</ref>
+[[Gaia DR4]] (expected December 2026) will further improve the statistical and systematic uncertainties in general, and the data pipelines for variable and multiple stars in particular.<ref name=brown2025>{{cite arXiv |last1=Brown |first1=Anthony G. A. |eprint=2503.01533v1 |title=Gaia: Ten Years of Surveying the Milky Way and Beyond |date=2025 |class=astro-ph.GA }}</ref> Multistar orbital solutions will become available, greatly aiding the study of Cepheids and Polaris, and in particular, may enable solving the outer AB orbit.<ref name=evans2024/>
 ==In popular culture==
@@ Line 390: / Line 481: @@
 Utsjoki.vaakuna.svg|Coat of arms of [[Utsjoki]]{{citation needed|date=August 2022}}
 </gallery>
+=== Ships ===
+* The [[Chinese spy ship Beijixing|Chinese spy ship ''Beijixing'']] is named after Polaris.
+* [[USS Polaris]] is named after Polaris
 ==Gallery==
@@ Line 396: / Line 491: @@
 Ursa Major - Ursa Minor - Polaris.jpg|[[Big Dipper]] and [[Ursa Minor]] in relation to Polaris
 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.
+File:Integrated Flux Nebula Surrounding Polaris - Kush Chandaria.jpg|Polaris, its surrounding [[Integrated Flux Nebula|integrated flux nebula]], and [[NGC188]]{{dubious|Photo of Polaris and IFN|date=October 2025|reason=This image is unlikely to be Polaris or an IFN}}
 </gallery>
-=== Ships ===
-* The [[Chinese spy ship Beijixing|Chinese spy ship ''Beijixing'']] is named after Polaris.
-* [[USS Polaris]] is named after Polaris
 ==See also==
@@ Line 411: / Line 501: @@
 * [[Polaris Flare]]
 * [[Regiment of the North Pole]]
+==Notes==
+{{notelist}}
 ==References==
@@ Line 450: / Line 543: @@
 [[Category:Suspected variables]]
 [[Category:Triple star systems]]
+[[Category:Population I stars]]
+[[Category:Lucidae]]

Polaris: Difference between revisions

Latest revision as of 00:58, 13 November 2025

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