Editing Polaris (section)

{{short description|Brightest star in the constellation 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}}
{{starbox begin
|name=Polaris
}}
{{Starbox image
 | image=
   {{Location mark
     | image=Ursa Minor constellation map.svg
     | float=center | width=250 | position=right
     | mark=Red circle.svg | mark_width=12 | mark_link=Polaris (star)
     | x%=49.5 | y%=4.5
   }}
 | caption=Location of Polaris (circled)
}}
{{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]]
| component1 = α UMi A
| ra1 = {{RA|02|31|49.09}}<ref name=hipparcos2/>
| dec1 = {{DEC|+89|15|50.8}}<ref name=hipparcos2/>
| appmag_v1 = 1.98<ref name=hst>{{Cite journal |last1 = Evans |first1 = N. R. |last2 = Schaefer |first2 = G. H. |last3 = Bond |first3 = H. E. |last4 = Bono |first4 = G. |last5 = Karovska |first5 = M. |last6 = Nelan |first6 = E. |last7 = Sasselov |first7 = D. |last8 = Mason |first8 = B. D. |doi = 10.1088/0004-6256/136/3/1137 |title = Direct Detection of the Close Companion of Polaris with The Hubble Space Telescope |journal = The Astronomical Journal |volume = 136 |issue = 3 |pages = 1137 |year = 2008 |arxiv = 0806.4904 |bibcode = 2008AJ....136.1137E |s2cid = 16966094 }}</ref> (1.86{{snd}}2.13)<ref name=gcvs/>
| component2 = α UMi B
| ra2 = {{RA|02|30|41.63}}<ref name="Gaia_DR3"/>
| dec2 = {{DEC|+89|15|38.1}}<ref name="Gaia_DR3"/>
| appmag_v2 = 8.7<ref name=hst/>
}}
{{Starbox character
| component = α UMi A
| type = <!--Type of star (e.g., main sequence star, protostar, white dwarf, neutron star, etc.)-->
| class = F7Ib + F6V<ref name=lee/>
| r-i = <!--R−I color-->
| v-r = <!--V−R color-->
| b-v = 0.60<ref name=hst/>
| u-b = 0.38<ref name=hst/>
| j-h = <!--J−H color-->
| j-k = <!--J−K color-->
| variable = [[Classical Cepheid]]<ref name=gcvs>{{cite journal | last1=Samus | first1=N. N. | last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V. | last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N. | display-authors=2 | title=General Catalogue of Variable Stars | version=5.1 | journal=Astronomy Reports | date=2017 | volume=61 | issue=1 | pages=80–88 | doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=125853869 }}</ref>
| component2 = α UMi B
| type2 = <!--Type of star (e.g., main sequence star, protostar, white dwarf, neutron star, etc.)-->
| class2 = F3V<ref name=hst/>
| r-i2 = <!--R−I color-->
| v-r2 = <!--V−R color-->
| b-v2 = 0.42<ref name=usenko/>
| u-b2 = 0.01<ref name=usenko/>
| j-h2 = <!--J−H color-->
| j-k2 = <!--J−K color-->
| variable2 = suspected<ref name=gcvs/>
}}
{{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_dec = {{val|-15|0.30}}<ref name=hipparcos2/>
 | parallax = 7.54
 | p_error = 0.11
 | parallax_footnote = <ref name=hipparcos2/>
 | dist_ly = {{val|{{convert|136.9|pc|ly|sigfig=4|disp=number}}|{{convert|0.34|pc|ly|sigfig=2|disp=number}}}}
 | dist_pc = {{val|136.90|0.34}}
 | dist_footnote = <ref name=evans2024/>
 | absmag_v = −3.6 (''α UMi Aa'')<ref name=hst/><br/>3.6 (''α UMi Ab'')<ref name=hst/><br/>3.1 (''α UMi B'')<ref name=hst/>
}}
{{Starbox relpos
| reference = <!-- Grand reference -->
| epoch = 2005.5880
| primary = α UMi Aa
| component = α UMi Ab
| angdistsec = 0.172
| angdistmas = <!--Angular distance, in milliarcseconds (alternatively, use angdistsec) -->
| angdistref = <!--Reference for angular distance -->
| posang = 231.4
| posangref = <!--Reference for position angle -->
| projsep = <!--Observed projected separation, in AU -->
| projsepref = <!--Reference for projected separation -->
}}
{{Starbox relpos
| reference = <!-- Grand reference -->
| epoch = 2005.5880
| primary = α UMi Aa
| component = α UMi B
| angdistsec = 18.217
| angdistmas = <!--Angular distance, in milliarcseconds (alternatively, use angdistsec) -->
| angdistref = <!--Reference for angular distance -->
| posang = 230.540
| posangref = <!--Reference for position angle -->
| projsep = <!--Observed projected separation, in AU -->
| projsepref = <!--Reference for projected separation -->
}}
{{Starbox orbit
| reference = <ref name=evans2024/>
| primary = α UMi Aa
| name = α UMi Ab
| period = {{val|29.416|0.028}}
| axis = {{val|0.12955|0.00205}}
| axis_unitless = {{val|2.90|0.03|p=≥|ul=AU}}<ref name=Anderson2019/>
| eccentricity = {{val|0.6354|0.0066}}
| inclination = {{val|127.57|1.22}}
| node = {{val|201.28|1.18}}
| periastron = {{val|2016.831|0.044}}
| periarg_primary = {{val|304.54|0.84}}
| k1 = {{val|3.762|0.025}}
| k2 = <!-- Velocity semi-amplitude (secondary in SB2), in km/s -->
}}
<!-- note, I have only included the Aa/Ab orbital information above. The A/B orbital information is below, should someone decide to either update the functionality of starbox orbit or add another instance of it.
| primsec_2 = B/A
| period_unitless_2 = ~100,000 years
| axis_unitless_2 = 32" (0.02 pc)
-->
{{Starbox detail
| component1              = α UMi Aa
| source                 =   <!--[source url]-->
| mass                   = {{val|5.13|0.28}}<ref name=evans2024/>
| radius                 =   {{val|46.27|0.42}}<ref name=evans2024/>
| luminosity_bolometric  =   1,260<ref name=fadeyev>{{cite journal |bibcode=2015MNRAS.449.1011F |arxiv=1502.06463 |doi = 10.1093/mnras/stv412 |title=Evolutionary status of Polaris|journal=Monthly Notices of the Royal Astronomical Society |volume=449 |issue=1 |pages=1011–1017 |year=2015 |last1=Fadeyev |first1=Y. A. |doi-access=free |s2cid=118517157}}</ref>
| gravity                =   2.2<ref name=usenko2005>{{Cite journal |last1 = Usenko |first1 = I. A. |last2 = Miroshnichenko |first2 = A. S. |last3 = Klochkova |first3 = V. G. |last4 = Yushkin |first4 = M. V. |title = Polaris, the nearest Cepheid in the Galaxy: Atmosphere parameters, reddening and chemical composition |doi = 10.1111/j.1365-2966.2005.09353.x |journal = Monthly Notices of the Royal Astronomical Society |volume = 362 |issue = 4 |pages = 1219 |year = 2005 |bibcode = 2005MNRAS.362.1219U |doi-access = free}}</ref>
| temperature            =   6015<ref name=usenko/>
| metal                  =   112% solar<ref name=strobel>{{Cite journal | last1 = Cayrel de Strobel | first1 = G. | last2 = Soubiran | first2 = C. | last3 = Ralite | first3 = N. | year = 2001 | title = Catalogue of [Fe/H] determinations for FGK stars: 2001 edition | journal = Astronomy and Astrophysics | volume = 373 | pages = 159–163 | arxiv = astro-ph/0106438| bibcode = 2001A&A...373..159C| doi = 10.1051/0004-6361:20010525 | s2cid = 17519049 }}</ref>
| 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>
}}
{{Starbox detail|no_heading=y
| source                 =   <!--[source url]-->
| component1             =   α UMi Ab
| mass                   =   1.316<ref name=evans2024/>
| radius                 =   1.04<ref name=hst/>
| luminosity_bolometric  =   3<ref name=hst/>
| age_myr                =   >500<ref name=neilson2021/>
| component2             =   α UMi B
| mass2                  =   1.39<ref name=hst/>
| radius2                =   1.38<ref name=usenko/>
| luminosity_bolometric2 =   3.9<ref name=usenko>{{Cite journal | last1 = Usenko | first1 = I. A. | last2 = Klochkova | first2 = V. G. | doi = 10.1111/j.1745-3933.2008.00426.x | title = Polaris B, an optical companion of the Polaris (α UMi) system: Atmospheric parameters, chemical composition, distance and mass | journal = Monthly Notices of the Royal Astronomical Society: Letters | volume = 387 | issue = 1 | pages = L1 | year = 2008 | doi-access = free |arxiv = 0708.0333 |bibcode = 2008MNRAS.387L...1U | s2cid = 18848139 }}</ref>
| gravity2               =   4.3<ref name=usenko/>
| temperature2           =   6900<ref name=usenko/>
| rotational_velocity2   =   110<ref name=usenko/>
| age_gyr2               =   1.5<ref name=neilson2021/>
}}
{{Starbox catalog
| names = {{odlist | name=Polaris, North Star, Cynosura | B=Alpha UMi, α UMi | ADS=1477 | CCDM=J02319+8915 }}
| component2 = α UMi A
| names2 = {{odlist | F=1 Ursae Minoris | HR=424 | BD=+88°8 | HD=8890 | SAO=308 | FK5=907 | GC=2243 | HIP=11767 }}
| component3 = α UMi B
| names3 = {{odlist | BD=+88°7 | SAO=305 | GC=2226 | NSV=631 }}
}}
{{Starbox reference
| Simbad = Polaris|sn=α UMi A
| Simbad2 = Polaris+B|sn2=α UMi B
}}
{{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>

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 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.