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Polaris

Topic: Astronomy

 From HandWiki - Reading time: 17 min
Short description: Brightest star in the constellation Ursa Minor
Polaris
Ursa Minor constellation map.svg
Red circle.svg
Location of Polaris (circled)
Observation data
{{#ifeq:J2000|J2000.0 (ICRS)|Epoch J2000.0      Equinox J2000.0 (ICRS)| Epoch J2000      [[Astronomy:Equinox (celestial coordinates)|Equinox J2000}}
Constellation Ursa Minor
Pronunciation /pəˈlɛərɪs, -ˈlær-/;
UK: /pəˈlɑːrɪs/[1]
α UMi A
Right ascension  02h 31m 49.09s[2]
Declination +89° 15′ 50.8″[2]
Apparent magnitude (V) 1.98[3] (1.86 – 2.13)[4]
α UMi B
Right ascension  02h 30m 41.63s[5]
Declination +89° 15′ 38.1″[5]
Apparent magnitude (V) 8.7[3]
Characteristics
α UMi A
Spectral type F7Ib[6]
U−B color index 0.38[3]
B−V color index 0.60[3]
Variable type Classical Cepheid[4]
α UMi B
Spectral type F3V[3]
U−B color index 0.01[7]
B−V color index 0.42[7]
Variable type suspected[4]
Astrometry
Radial velocity (Rv)−17[8] km/s
Proper motion (μ) RA: 198.8±0.20[2] mas/yr
Dec.: −15±0.30[2] mas/yr
Parallax (π)7.54 ± 0.11[2] mas
Distance323–433[9] ly
(99–133[9] pc)
Absolute magnitude (MV)−3.6 (α UMi Aa)[3]
3.6 (α UMi Ab)[3]
3.1 (α UMi B)[3]
Position (relative to α UMi Aa)
Componentα UMi Ab
Epoch of observation2005.5880
Angular distance0.172″
Position angle231.4°
Position (relative to α UMi Aa)
Componentα UMi B
Epoch of observation2005.5880
Angular distance18.217″
Position angle230.540°
Orbit[10]
Primaryα UMi Aa
Companionα UMi Ab
Period (P)29.59±0.02 yr
Semi-major axis (a)0.1204±0.0059"
(≥2.90±0.03 astronomical unit|AU[11])
Eccentricity (e)0.608±0.005
Inclination (i)146.2±10.9°
Longitude of the node (Ω)191.4±4.9°
Periastron epoch (T)1987.66±0.13
Argument of periastron (ω)
(secondary)		123.01±0.75°
Semi-amplitude (K1)
(primary)		3.72±0.03 km/s
Details
α UMi Aa
Mass5.4[12] M☉
Radius37.5[12] R☉
Luminosity (bolometric)1,260[12] L☉
Surface gravity (log g)2.2[13] cgs
Temperature6015[7] K
Metallicity112% solar[14]
Rotation119 days[6]
Rotational velocity (v sin i)14[6] km/s
Age45 - 67[15] Myr
α UMi Ab
Mass1.26[3] M☉
Radius1.04[3] R☉
Luminosity (bolometric)3[3] L☉
Age>500[15] Myr
α UMi B
Mass1.39[3] M☉
Radius1.38[7] R☉
Luminosity (bolometric)3.9[7] L☉
Surface gravity (log g)4.3[7] cgs
Temperature6900[7] K
Rotational velocity (v sin i)110[7] km/s
Age1.5[15] Gyr
Other designations
α UMi A: {{{names2}}}
α UMi B: {{{names3}}}
Database references
SIMBADα UMi A
α UMi B

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 or Pole 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.

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 433 light-years (133 parsecs), while the successor mission Gaia gives a distance of about 448 light-years (137 parsecs). Calculations by other methods vary widely.

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.

Stellar system

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 (M☉). It is the first classical Cepheid to have a mass determined from its orbit. The two smaller companions are Polaris B, a 1.39 M☉ F3 main-sequence star orbiting at a distance of 2,400 astronomical units (AU),[17] and Polaris Ab (or P), a very close F6 main-sequence star with a mass of 1.26 M☉.[3] Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a reflecting telescope of his own,[18] one of the best telescopes of the time. In January 2006, NASA released images, from the Hubble telescope, that showed the three members of the Polaris ternary system.[19][20]

The variable radial velocity of Polaris A was reported by W. W. Campbell in 1899, which suggested this star is a binary system.[21] 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.[22] 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.[23]

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.[24] K. W. Kamper in 1996 produced refined elements with a period of 29.59±0.02 years and an eccentricity of 0.608±0.005.[25] In 2019, a study by R. I. Anderson gave a period of 29.32±0.11 years with an eccentricity of 0.620±0.008.[11]

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.[17][26]

Observation

Variability

A light curve for Polaris, plotted from TESS data[27]

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,[11] is heavily studied. The variability of Polaris had been suspected since 1852; this variation was confirmed by Ejnar Hertzsprung in 1911.[28]

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]

Polaris and its surrounding 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 (lower temperature) evolution across the Cepheid instability strip, but it may be due to interference between the primary and the first-overtone pulsation modes.[20][29][30] 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.[12][30][31]

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.[13]

Research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, changing from third to second magnitude.[32] 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".

Role as pole star

Main page: Astronomy:Pole star
A typical Northern Hemisphere star trail with Polaris in the center.

Because Polaris lies nearly in a direct line with the Earth's rotational axis "above" the North Pole—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 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.[33] 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[34] 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.[35] 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.

The celestial pole was close to Thuban around 2750 BC,[35] and during classical antiquity it was slightly closer to Kochab (β UMi) than to Polaris, although still about 10° from either star.[36] 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".[37] In Shakespeare's play Julius Caesar, 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 lying half way between the asterisms Cassiopeia and the Big Dipper

Polaris was referenced in Nathaniel Bowditch's 1802 book, American Practical Navigator, where it is listed as one of the navigational stars.[38]

Names

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

The modern name Polaris[39] is shortened from Neo-Latin stella polaris "polar star", coined in the Renaissance when the star had approached the celestial pole to within a few degrees. 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.[40]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[41] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[42] 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 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") [citation needed]. In the Old English rune poem, the T-rune is apparently associated with "a circumpolar constellation", or the planet Mars.[43]

In the Hindu Puranas, it became personified under the name Dhruva ("immovable, fixed").[44] 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)[45] An older English name, attested since the 14th century, is lodestar "guiding star", cognate with the Old Norse leiðarstjarna, Middle High German leitsterne.[46]

The ancient name of the constellation Ursa Minor, Cynosura (from the Greek κυνόσουρα "the dog's tail"),[47] 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. [citation needed]

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),[48] and that name was used in medieval Islamic astronomy as well.[49][50] 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.

Polaris pictured in the flag of Nunavut

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." In Julius Caesar, he has Caesar 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, but this is only noticeable over centuries.[citation needed]

In Inuit astronomy, Polaris is known as Niqirtsuituq (syllabics: ᓂᕿᕐᑦᓱᐃᑐᖅ). It is depicted on the flag and coat of arms of the Canada Inuit territory of Nunavut, as well as on the flag of the United States state of Alaska.[51]

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 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.[52]

The Plains Cree call the star in Nehiyawewin: acâhkos êkâ kâ-âhcît "the star that does not move" (syllabics: ᐊᒑᐦᑯᐢ ᐁᑳ ᑳ ᐋᐦᒌᐟ).[53] In Mi'kmawi'simk the star is named Tatapn.[54]

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.[citation needed]

Distance

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)

Many recent papers calculate the distance to Polaris at about 433 light-years (133 parsecs),[20] 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).[9] Polaris is the closest Cepheid variable to Earth so its physical parameters are of critical importance to the whole astronomical distance scale.[9] It is also the only one with a dynamically measured mass.

Selected distance estimates to Polaris
Year Component Distance, ly (pc) Notes
2006 A 330 ly (101 pc) Turner[29]
2007[A] A 433 ly (133 pc) Hipparcos[2]
2008 B 359 ly (110 pc) Usenko & Klochkova[7]
2013 B 323 ly (99 pc) Turner, et al.[9]
2014 A ≥ 385 ly (≥ 118 pc) Neilson[55]
2018 B 521 ly (160pc) Bond et al.[56]
2018 B 445.3 ly (136.6 pc)[B] Gaia DR2[57]
2020 B 447.6 ly (137.2pc) Gaia DR3[5]
A New revision of observations from 1989–1993, first published in 1997
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 milliarcseconds (970 microarcseconds), and it obtained accurate measurements for stellar distances up to 1,000 pc away.[58] The Hipparcos data was examined again with more advanced error correction and statistical techniques.[2] 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.[9] The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about the distance.[59]

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).[60] 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.[61] 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".[62] Gaia Data Release 2 does not include a parallax for Polaris, but a distance inferred from it is 136.6±0.5 pc (445.5 ly) for Polaris B,[57] somewhat further than most previous estimates and several times more accurate. This was further improved to 137.2±0.3 pc (447.6 ly), upon publication of the Gaia Data Release 3 catalog on 13 June 2022 which superseded Gaia Data Release 2.[5]

Gallery

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

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

  • Polaris pictured in the coat of arms of Utsjoki[citation needed]

See also

References

  1. ↑ "Polaris | meaning in the Cambridge English Dictionary". https://dictionary.cambridge.org/dictionary/english/polaris. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 Evans, N. R.; Schaefer, G. H.; Bond, H. E.; Bono, G.; Karovska, M.; Nelan, E.; Sasselov, D.; Mason, B. D. (2008). "Direct Detection of the Close Companion of Polaris with The Hubble Space Telescope". The Astronomical Journal 136 (3): 1137. doi:10.1088/0004-6256/136/3/1137. Bibcode: 2008AJ....136.1137E. 
  4. ↑ 4.0 4.1 4.2 4.3 Samus, N. N.; Kazarovets, E. V. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  5. ↑ 5.0 5.1 5.2 5.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  6. ↑ 6.0 6.1 6.2 6.3 Lee, B. C.; Mkrtichian, D. E.; Han, I.; Park, M. G.; Kim, K. M. (2008). "Precise Radial Velocities of Polaris: Detection of Amplitude Growth". The Astronomical Journal 135 (6): 2240. doi:10.1088/0004-6256/135/6/2240. Bibcode: 2008AJ....135.2240L. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Usenko, I. A.; Klochkova, V. G. (2008). "Polaris B, an optical companion of the Polaris (α UMi) system: Atmospheric parameters, chemical composition, distance and mass". Monthly Notices of the Royal Astronomical Society: Letters 387 (1): L1. doi:10.1111/j.1745-3933.2008.00426.x. Bibcode: 2008MNRAS.387L...1U. 
  8. ↑ Campbell, William Wallace (1913). "The radial velocities of 915 stars". Lick Observatory Bulletin 229: 113. doi:10.5479/ADS/bib/1913LicOB.7.113C. Bibcode: 1913LicOB...7..113C. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Turner, D. G.; Kovtyukh, V. V.; Usenko, I. A.; Gorlova, N. I. (2013). "The Pulsation Mode of the Cepheid Polaris". The Astrophysical Journal Letters 762 (1): L8. doi:10.1088/2041-8205/762/1/L8. Bibcode: 2013ApJ...762L...8T. 
  10. ↑ Evans, N. R. et al. (2018). "The Orbit of the Close Companion of Polaris: Hubble Space Telescope Imaging, 2007 to 2014". The Astrophysical Journal 863 (2): 187. doi:10.3847/1538-4357/aad410. Bibcode: 2018ApJ...863..187E. 
  11. ↑ 11.0 11.1 11.2 Anderson, R. I. (March 2019). "Probing Polaris' puzzling radial velocity signals. Pulsational (in-)stability, orbital motion, and bisector variations". Astronomy & Astrophysics 623: 17. doi:10.1051/0004-6361/201834703. A146. Bibcode: 2019A&A...623A.146A. 
  12. ↑ 12.0 12.1 12.2 12.3 Fadeyev, Y. A. (2015). "Evolutionary status of Polaris". Monthly Notices of the Royal Astronomical Society 449 (1): 1011–1017. doi:10.1093/mnras/stv412. Bibcode: 2015MNRAS.449.1011F. 
  13. ↑ 13.0 13.1 Usenko, I. A.; Miroshnichenko, A. S.; Klochkova, V. G.; Yushkin, M. V. (2005). "Polaris, the nearest Cepheid in the Galaxy: Atmosphere parameters, reddening and chemical composition". Monthly Notices of the Royal Astronomical Society 362 (4): 1219. doi:10.1111/j.1365-2966.2005.09353.x. Bibcode: 2005MNRAS.362.1219U. 
  14. ↑ Cayrel de Strobel, G.; Soubiran, C.; Ralite, N. (2001). "Catalogue of [Fe/H] determinations for FGK stars: 2001 edition". Astronomy and Astrophysics 373: 159–163. doi:10.1051/0004-6361:20010525. Bibcode: 2001A&A...373..159C. 
  15. ↑ 15.0 15.1 15.2 Neilson, H. R.; Blinn, H. (2021). "The Curious Case of the North Star: The Continuing Tension Between Evolution Models and Measurements of Polaris". RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators. 529. p. 72. Bibcode: 2021ASPC..529...72N. 
  16. ↑ 16.0 16.1 Kaler, Jim. "Polaris (Alpha Ursae Minoris)". http://stars.astro.illinois.edu/sow/polaris.html. 
  17. ↑ 17.0 17.1 Wielen, R.; Jahreiß, H.; Dettbarn, C.; Lenhardt, H.; Schwan, H. (2000). "Polaris: Astrometric orbit, position, and proper motion". Astronomy and Astrophysics 360: 399–410 [400–402, 406]. Bibcode: 2000A&A...360..399W. 
  18. ↑ Argyle, Bob et al. (August 29, 2019). An Anthology of Visual Double Stars. Cambridge University Press. p. 265. ISBN 9781108601702. https://books.google.com/books?id=jSmqDwAAQBAJ&pg=PT265. 
  19. ↑ "There's More to the North Star Than Meets the Eye". Hubblesite.org. 2006-01-09. https://hubblesite.org/contents/news-releases/2006/news-2006-02.html. 
  20. ↑ 20.0 20.1 20.2 Evans, N. R.; Sasselov, D. D.; Short, C. I. (2002). "Polaris: Amplitude, Period Change, and Companions". The Astrophysical Journal 567 (2): 1121. doi:10.1086/338583. Bibcode: 2002ApJ...567.1121E. 
  21. ↑ Campbell, W. W. (October 1899). "On the variable velocity of Polaris in the line of sight". Publications of the Astronomical Society of the Pacific 11: 195–199. doi:10.1086/121339. Bibcode: 1899PASP...11..195C. 
  22. ↑ Moore, J. H. (August 1927). "Note on the Longitude of the Lick Observatory". Publications of the Astronomical Society of the Pacific 39 (230): 249. doi:10.1086/123734. Bibcode: 1927PASP...39..249M. 
  23. ↑ Roemer, Elizabeth (May 1965). "Orbital Motion of Alpha Ursae Minoris from Radial Velocities". Astrophysical Journal 141: 1415. doi:10.1086/148230. Bibcode: 1965ApJ...141.1415R. 
  24. ↑ Wyller, A. A. (December 1957). "Parallax and orbital motion of spectroscopic binary Polaris from photographs taken with the 24-inch Sproul refractor.". Astronomical Journal 62: 389–393. doi:10.1086/107559. Bibcode: 1957AJ.....62..389W. 
  25. ↑ Kamper, Karl W. (June 1996). "Polaris Today". Journal of the Royal Astronomical Society of Canada 90: 140. Bibcode: 1996JRASC..90..140K. 
  26. ↑ Evans, Nancy Remage; Guinan, Edward; Engle, Scott; Wolk, Scott J.; Schlegel, Eric; Mason, Brian D.; Karovska, Margarita; Spitzbart, Bradley (2010). "Chandra Observation of Polaris: Census of Low-mass Companions". The Astronomical Journal 139 (5): 1968. doi:10.1088/0004-6256/139/5/1968. Bibcode: 2010AJ....139.1968E. 
  27. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  28. ↑ Hertzsprung, Ejnar (August 1911). "Nachweis der Veränderlichkeit von α Ursae Minoris" (in de). Astronomische Nachrichten 189 (6): 89. doi:10.1002/asna.19111890602. Bibcode: 1911AN....189...89H. https://zenodo.org/record/1424878. 
  29. ↑ 29.0 29.1 Turner, D. G.; Savoy, J.; Derrah, J.; Abdel‐Sabour Abdel‐Latif, M.; Berdnikov, L. N. (2005). "The Period Changes of Polaris". Publications of the Astronomical Society of the Pacific 117 (828): 207. doi:10.1086/427838. Bibcode: 2005PASP..117..207T. 
  30. ↑ 30.0 30.1 Neilson, H. R.; Engle, S. G.; Guinan, E.; Langer, N.; Wasatonic, R. P.; Williams, D. B. (2012). "The Period Change of the Cepheid Polaris Suggests Enhanced Mass Loss". The Astrophysical Journal 745 (2): L32. doi:10.1088/2041-8205/745/2/L32. Bibcode: 2012ApJ...745L..32N. 
  31. ↑ Engle, Scott G; Guinan, Edward F; Harmanec, Petr (2018). "Toward Ending the Polaris Parallax Debate: A Precise Distance to Our Nearest Cepheid from Gaia DR2". Research Notes of the AAS 2 (3): 126. doi:10.3847/2515-5172/aad2d0. Bibcode: 2018RNAAS...2..126E. 
  32. ↑ Irion, R (2004). "American Astronomical Society meeting. As inconstant as the Northern Star". Science 304 (5678): 1740–1. doi:10.1126/science.304.5678.1740b. PMID 15205508. 
  33. ↑ Meeus, J. (1990). "Polaris and the North Pole". Journal of the British Astronomical Association 100: 212. Bibcode: 1990JBAA..100..212M. 
  34. ↑ "A visual method to correct a ship's compass using Polaris using Ursa Major as a point of reference". http://www.kaizad.co.uk/data/Nav/Polaris.xls. 
  35. ↑ 35.0 35.1 Ridpath, Ian, ed (2004). Norton's Star Atlas. New York: Pearson Education. p. 5. ISBN 978-0-13-145164-3. https://archive.org/details/nortonsstaratlas00ianr/page/5. "Around 4800 years ago Thuban (α Draconis) lay a mere 0°.1 from the pole. Deneb (α Cygni) will be the brightest star near the pole in about 8000 years' time, at a distance of 7°.5." 
  36. ↑ Ridpath, Ian (2018). "Ursa Minor, the Little Bear". Star Tales. http://www.ianridpath.com/startales/ursaminor.html#polaris. 
  37. ↑ Columbus, Ferdinand (1960). The Life of the Admiral Christopher Columbus by His Son Fredinand. London: Folio Society. p. 74. 
  38. ↑ Bowditch, Nathaniel; National Imagery and Mapping Agency (2002). "15". The American practical navigator : an epitome of navigation. Paradise Cay Publications. p. 248. ISBN 978-0-939837-54-0. https://books.google.com/books?id=pXjHDnIE_ygC&pg=PR1. 
  39. ↑ IAU Working Group on Star Names "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt. 
  40. ↑ Gemmae Frisii de astrolabo catholico liber: quo latissime patentis instrumenti multiplex usus explicatur, & quicquid uspiam rerum mathematicarum tradi possit continetur. Steelsius. 1556. p. 20. https://books.google.com/books?id=8XE6AAAAcAAJ&pg=PA20. ; see also Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Publishing. p. 23. ISBN 978-1-931559-44-7. 
  41. ↑ "International Astronomical Union | IAU". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  42. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1". https://www.iau.org/static/science/scientific_bodies/working_groups/280/WGSN_bulletin1.pdf. 
  43. ↑ Dickins, Bruce (1915). Runic and heroic poems of the old Teutonic peoples. p. 18. ; Dickins' "a circumpolar constellation" is attributed to L. Botkine, La Chanson des Runes (1879).
  44. ↑ Daniélou, Alain (1991). The Myths and Gods of India: The Classic Work on Hindu Polytheism. Princeton/Bollingen (1964); Inner Traditions/Bear & Co. p. 186. ISBN 978-0-892-813544. https://books.google.com/books?id=1HMXN9h6WX0C&pg=PA186. 
  45. ↑ Halliwell, J. O., ed (1856). The Works of William Shakespeare. 5. p. 40. https://books.google.com/books?id=7NVfAAAAcAAJ&pg=PA40. 
  46. ↑ Kluge, Friedrich; Götze, Alfred (1943). Etymologisches Wörterbuch der deutschen Sprache. Walter de Gruyter. p. 355. ISBN 978-3-111-67185-7. https://books.google.com/books?id=R1K9DwAAQBAJ&pg=PA355. 
  47. ↑ Ridpath, Ian (28 June 2018). Star Tales. Lutterworth Press. ISBN 978-0-7188-4782-1. https://books.google.com/books?id=-dXYDwAAQBAJ. 
  48. ↑ ʻAbd al-Raḥmān ibn ʻUmar Ṣūfī (1874). Description des Etoiles fixes. Commissionnaires de lÁcadémie Impériale des sciences. p. 45. https://books.google.com/books?id=nJRHAAAAYAAJ&pg=PA45. 
  49. ↑ Al-Sufi, AbdulRahman (964). "Book Of Fixed Stars". http://gallica.bnf.fr/ark:/12148/btv1b60006156/f48.item. 
  50. ↑ Schjellerup, Hans (1874). Description des Etoiles fixes. p. 45. https://books.google.com/books?id=nJRHAAAAYAAJ&pg=PA45. 
  51. ↑ "The Coat of Arms of Nunavut. (n.d.)". https://assembly.nu.ca/about-legislative-assembly/coat-arms-nunavut. 
  52. ↑ "Winter Solstice is Sacred Time a Time to Carry One Another by Dakota Wind". https://lastrealindians.com/news/2019/12/26/winter-solstice-is-sacred-time-a-time-to-carry-one-another-by-dakota-wind. 
  53. ↑ "Polaris". https://dictionary.plainscree.atlas-ling.ca/. 
  54. ↑ Lebans, Jim (29 September 2022). "Mi'kmaw astronomer says we should acknowledge we live under Indigenous skies". Canadian Broadcasting Corporation. https://www.cbc.ca/radio/quirks/oct-1-redirecting-an-asteroid-rainforest-politics-wildlife-and-covid-and-more-1.6599378/mi-kmaw-astronomer-says-we-should-acknowledge-we-live-under-indigenous-skies-1.6600279. 
  55. ↑ Neilson, H. R. (2014). "Revisiting the fundamental properties of the Cepheid Polaris using detailed stellar evolution models". Astronomy & Astrophysics 563: A48. doi:10.1051/0004-6361/201423482. Bibcode: 2014A&A...563A..48N. 
  56. ↑ Bond, Howard E; Nelan, Edmund P; Remage Evans, Nancy; Schaefer, Gail H; Harmer, Dianne (2018). "Hubble Space Telescope Trigonometric Parallax of Polaris B, Companion of the Nearest Cepheid". The Astrophysical Journal 853 (1): 55. doi:10.3847/1538-4357/aaa3f9. Bibcode: 2018ApJ...853...55B. 
  57. ↑ 57.0 57.1 Bailer-Jones, C. A. L; Rybizki, J; Fouesneau, M; Mantelet, G; Andrae, R (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal 156 (2): 58. doi:10.3847/1538-3881/aacb21. Bibcode: 2018AJ....156...58B. 
  58. ↑ Van Leeuwen, F. (1997). "The Hipparcos Mission". Space Science Reviews 81 (3/4): 201–409. doi:10.1023/A:1005081918325. Bibcode: 1997SSRv...81..201V. 
  59. ↑ Van Leeuwen, F. (2013). "The HIPPARCOS parallax for Polaris". Astronomy & Astrophysics 550: L3. doi:10.1051/0004-6361/201220871. Bibcode: 2013A&A...550L...3V. 
  60. ↑ Liu, C.; Bailer-Jones, C. A. L.; Sordo, R.; Vallenari, A. et al. (2012). "The expected performance of stellar parametrization with Gaia spectrophotometry". Monthly Notices of the Royal Astronomical Society 426 (3): 2463. doi:10.1111/j.1365-2966.2012.21797.x. Bibcode: 2012MNRAS.426.2463L. 
  61. ↑ Martín-Fleitas, J.; Sahlmann, J.; Mora, A.; Kohley, R.; Massart, B.; l'Hermitte, J.; Le Roy, M.; Paulet, P. (2014). "Enabling Gaia observations of naked-eye stars". Space Telescopes and Instrumentation 2014: Optical. Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave 9143: 91430Y. doi:10.1117/12.2056325. Bibcode: 2014SPIE.9143E..0YM. 
  62. ↑ T. Prusti (2016), "The Gaia mission", Astronomy and Astrophysics 595: A1, doi:10.1051/0004-6361/201629272, Bibcode: 2016A&A...595A...1G 


Coordinates: Sky map 02h 31m 48.7s, +89° 15′ 51″

Preceded by
Kochab & Pherkad 		Pole star
500–3000 		Succeeded by
Gamma Cephei



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