Editing Polaris (section)

==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)]]
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.

{| class="wikitable plainrowheaders" style="margin-right: 0; margin-left: 1em; text-align: center;"
|+ Selected distance estimates to Polaris
! scope="col" | Year
! scope="col" | Component
! scope="col" | Distance, [[light-year|ly]] ([[parsec|pc]])
! scope="col" | Notes
|-
! scope="row" | 2006
| A
| 330 ly (101 pc)
| Turner<ref name=turner/>
|-
! scope="row" | 2007{{ref label|2007|A|A}}
| A
| 433 ly (133 pc)
| Hipparcos<ref name=hipparcos2/>
|-
! scope="row" | 2008
| B
| 359 ly (110 pc)
| Usenko & Klochkova<ref name=usenko/>
|-
! scope="row" | 2013
| B
| 323 ly (99 pc)
| Turner, et al.<ref name=turner2012/>
|-
! scope="row" | 2014
| A
| ≥ 385 ly (≥ 118 pc)
| 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>
|-
! scope="row" | 2018
| B
| 521 ly (160pc)
| 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>
|-
! scope="row" | 2018
| B
| 445.3 ly (136.6 pc){{ref label|2018|B|B}}
| Gaia DR2<ref name=bailer-jones/>
|-
! scope="row" | 2020
| B
| 447.6 ly (137.2pc)
| Gaia DR3<ref name="Gaia_DR3"/>
|}
{| style="margin-right: 0; margin-left: 1em;"
|-
|{{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>

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>