Editing Polaris (section)

===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: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]].]]
Because Polaris lies nearly in a direct line with the [[Earth's rotation]]al 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.<ref name=Kaler/>

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.<ref>{{cite journal |bibcode=1990JBAA..100..212M |title=Polaris and the North Pole |last1=Meeus |first1=J. |journal=Journal of the British Astronomical Association |year=1990 |volume=100 |page=212 }}</ref> Because it is so close to the celestial north pole, its [[right ascension]] is changing rapidly due to the [[Axial precession|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<ref name="kaizad_co_uk" /> is made using the leading edge of the "[[Big Dipper]]" [[Asterism (astronomy)|asterism]] in the constellation Ursa Major. The leading edge (defined by the stars [[Alpha Ursae Majoris|Dubhe]] and [[Beta Ursae Majoris|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]].<ref name="Nor">{{cite book | title=Norton's Star Atlas | date=2004 | publisher=Pearson Education | isbn=978-0-13-145164-3 | editor-last=Ridpath | editor-first=Ian | location=New York | page=[https://archive.org/details/nortonsstaratlas00ianr/page/5 5] | quote=Around 4800 years ago Thuban ({{GreekFont|α}} Draconis) lay a mere 0°.1 from the pole. Deneb ({{GreekFont|α}} Cygni) will be the brightest star near the pole in about 8000 years' time, at a distance of 7°.5. | url-access=registration | url=https://archive.org/details/nortonsstaratlas00ianr/page/5 }}</ref> The celestial pole will move away from α UMi after the 21st century, passing close by [[Gamma Cephei]] by about the [[5th millennium#Astronomical events|41st century]], moving towards [[Deneb]] by about the [[10th millennium#Astronomical events|91st century]].{{fact|date=January 2025}}

The celestial pole was close to [[Thuban]] around 2750 BCE,<ref name="Nor" /> and during [[classical antiquity]] it was slightly closer to [[Beta Ursae Minoris|Kochab]] (β UMi) than to Polaris, although still about {{val|10|ul=°}} from either star.<ref>{{cite web | first=Ian | last=Ridpath | url=http://www.ianridpath.com/startales/ursaminor.html#polaris | work=Star Tales | title=Ursa Minor, the Little Bear | date=2018 | access-date=20 August 2016 }}</ref> 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".<ref>{{cite book | title=The Life of the Admiral Christopher Columbus by His Son Fredinand | first=Ferdinand | last=Columbus | author-link=Ferdinand Columbus |translator-link=Benjamin Keen | translator1-first=Benjamin | translator1-last=Keen | publication-place=London | publisher=Folio Society | date=1960 | page=74 }}</ref> In [[William Shakespeare|Shakespeare's]] play [[Julius Caesar (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.<ref>{{Cite news |last=Geary |first=Aidan |date=June 30, 2018 |title=Look up, be patient and 'think about how big the universe is': Expert tips for stargazing this summer |url=https://www.cbc.ca/news/canada/manitoba/stargazing-constellations-how-to-1.4726939 |access-date=June 29, 2024 |work=[[Canadian Broadcasting Corporation]]}}</ref>

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]].<ref name="BowditchAgency2002">{{cite book | title=The American practical navigator : an epitome of navigation | first1=Nathaniel | last1=Bowditch | author2=National Imagery and Mapping Agency | publisher=Paradise Cay Publications | year=2002 | isbn=978-0-939837-54-0 | page=248 | chapter=15 | author1-link=Nathaniel Bowditch | chapter-url=https://books.google.com/books?id=pXjHDnIE_ygC&pg=PR1}}</ref>