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{{short description|Најсјајнија звезда у сазвежђу Малог медведа}}{{rut}}
[[Датотека:Polaris alpha ursae minoris.jpg|мини|300п|Severnjača i [[sazvežđe]] [[Veliki medved (sazvežđe)|Velikog]] i [[Mali medved (sazvežđe)|Malog medveda]] (levo). Komponente sistema snimljene [[Teleskop Habl|Habl svemirskim teleskopom]] (desno).]]
{{starbox begin
'''Zvezda severnjača''' ({{jez-lat-lat|Polaris}}) je zvezda najbliža [[nebeski ekvatorijalni koordinatni sistem|severnom nebeskom polu]] [[Zemlja|Zemlje]] ([[2006]] godine je bila udaljena od njega 42'). Najsjanija je zvezda [[sazvežđe|sazvežđa]] [[Mali medved (sazvežđe)|Mali medved]] ([[prividna zvezdana veličina|relativna magnituda]] 1,97), pa nosi i oznaku α -{Ursa Minoris}- (α-{UMi}-). Vidi se samo sa severne hemisfere, na kojoj je i [[cirkumpolarnost|cirkumpolarna]]. Zahvaljujući svom položaju na noćnom nebu kao i relativno lakoj uočljivosti, koristi se za orijentaciju. Od Zemlje je udaljena 430±30 [[svetlosna godina|svetlosnih godina]].
|name=Polaris
}}
{{Starbox image-lat
| image =
{{Location mark
| image = Ursa Minor IAU.svg | width = 280 | float = center
| alt = Chart showing star positions and boundaries of the Ursa Minor constellation
| mark = Red circle.svg | mark_width = 15
| x = 499 | y = 220
}}
| caption = Polaris (α Ursae Minoris, circled in red) in the constellation Ursa Minor (white area)
}}
{{Starbox observe 3s-lat
| 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 Aa
| ra1 = {{RA|02|31|49.09}}
| dec1 = {{DEC|+89|15|50.8}}
| 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> (variable 1.86–2.13)
| component2 = α UMi Ab
| ra2 = <!--Right Ascension of the second component-->
| dec2 = <!--Declination of the second component-->
| appmag_v2 = 9.2<ref name=hst/>
| component3 = α UMi B
| ra3 = {{RA|02|30|41.63}}
| dec3 = {{DEC|+89|15|38.1}}
| appmag_v3 = 8.7<ref name=hst/>
}}
{{Starbox character-lat
| component = α UMi Aa
| type = <!--Type of star (e.g., main sequence star, protostar, white dwarf, neutron star, etc.)-->
| class = F7Ib<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 Ab
| type2 = <!--Type of star (e.g., main sequence star, protostar, white dwarf, neutron star, etc.)-->
| class2 = F6V<ref name=hst/>
}}
{{Starbox character-lat |no_heading=y
| component = α UMi B
| type = <!--Type of star (e.g., main sequence star, protostar, white dwarf, neutron star, etc.)-->
| class = F3V<ref name=hst/>
| r-i = <!--R−I color-->
| v-r = <!--V−R color-->
| b-v = 0.42<ref name=usenko/>
| u-b = 0.01<ref name=usenko/>
| j-h = <!--J−H color-->
| j-k = <!--J−K color-->
| variable =
}}
{{Starbox astrometry-lat
| radial_v = −17
| prop_mo_ra = 198.8±0.20
| prop_mo_dec = -15±0.30
| parallax = 7.54
| p_error = 0.11
| parallax_footnote = <ref name=hipparcos2/>
| dist_ly = 323–433<ref name=turner2012/>
| dist_pc = 99–133<ref name=turner2012/>
| 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 orbit-lat
| reference = <ref name=hst2>{{Cite journal
| title=The Orbit of the Close Companion of Polaris: Hubble Space Telescope Imaging, 2007 to 2014
| last1=Evans | first1=N. R. | last2=Marovska | first2=M.
| last3=Bond | first3=H. E. | last4=Schaefer | first4=G. H.
| last5=Sahu | first5=K. C. | last6=Mack | first6=J.
| last7=Nelan | first7=E. P. | last8=Gallene | first8=A.
| last9=Tingle | first9=E. D. | display-authors=1
| journal=The Astrophysical Journal
| volume=863 | issue=2 | pages=187 | year=2018
| arxiv=1807.06115 | bibcode=2018ApJ...863..187E
| doi=10.3847/1538-4357/aad410 | s2cid=119392532 }}</ref>
| primary = α UMi Aa
| name = α UMi Ab
| period = 29.59 ± 0.02
| axis = 0.1204 ± 0.0059
| axis_unitless = {{val|2.90|0.03|p=≥|ul=AU}}<ref name=Anderson2019/>
| eccentricity = 0.608 ± 0.005
| inclination = 146.2 ± 10.9
| node = 191.4 ± 4.9
| periastron = 1987.66 ± 0.13
| periarg = 123.01 ± 0.75
| periarg_primary = <!--Argument of periastron (in degrees), primary -->
| k1 = 3.72 ± 0.03
| k2 =
}}
{{Starbox detail-lat
| component1 = α UMi Aa
| source = <!--[source url]-->
| mass = 5.4<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. |s2cid=118517157}}</ref>
| radius = 37.5<ref name=fadeyev/>
| luminosity_bolometric = 1,260<ref name=fadeyev/>
| 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 = 70<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 |last1 = Wielen |first1 = R. |last2 = Jahreiß |first2 = H. |last3 = Dettbarn |first3 = C. |last4 = Lenhardt |first4 = H. |last5 = Schwan |first5 = H. |year = 2000 }}</ref>
}}
{{Starbox detail-lat
|no_heading=y
| source = <!--[source url]-->
| component1 = α UMi Ab
| mass = 1.26<ref name=hst/>
| radius = 1.04<ref name=hst/>
| luminosity_bolometric = 3<ref name=hst/>
| age_myr = 70<ref name=Wielen/>
| 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 |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/>
| age2_myr = 70<ref name=Wielen/>
}}
{{Starbox relpos-lat
| 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-lat
| 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 catalog-lat
| names = {{odlist | name=Polaris, North Star, Cynosura, Alruccabah, Phoenice, Navigatoria, Star of Arcady, Yilduz, Mismar | B=Alpha UMi, α UMi | F=1 Ursae Minoris | HR=424 | BD=+88° 8 | HD=8890 | SAO=308 | FK5=907 | GC=2243 | ADS=1477 | CCDM=J02319+8915 | HIP=11767 }}
}}
{{Starbox reference-lat
| Simbad = Polaris|sn=α UMi A
| Simbad2 = Polaris+B|sn2=α UMi B
}}
{{starbox end}}

'''Zvezda severnjača''' ({{jez-lat-lat|Polaris}}) je zvezda najbliža [[nebeski ekvatorijalni koordinatni sistem|severnom nebeskom polu]] [[Zemlja|Zemlje]] ([[2006]] godine je bila udaljena od njega 42').<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> Najsjanija je zvezda [[sazvežđe|sazvežđa]] [[Mali medved (sazvežđe)|Mali medved]] ([[prividna zvezdana veličina|relativna magnituda]] 1,97), pa nosi i oznaku α&nbsp;-{Ursa Minoris}- (α-{UMi}-). Vidi se samo sa severne hemisfere, na kojoj je i [[cirkumpolarnost|cirkumpolarna]]. Zahvaljujući svom položaju na noćnom nebu kao i relativno lakoj uočljivosti, koristi se za orijentaciju. Od Zemlje je udaljena 430±30 [[svetlosna godina|svetlosnih godina]].


== Komponente sistema ==
== Komponente sistema ==
[[Датотека:Polaris alpha ursae minoris.jpg|мини|250п|left|Severnjača i [[sazvežđe]] [[Veliki medved (sazvežđe)|Velikog]] i [[Mali medved (sazvežđe)|Malog medveda]] (levo). Komponente sistema snimljene [[Teleskop Habl|Habl svemirskim teleskopom]] (desno).]]

Zvezda severnjača predstavlja sistem sastavljen od 3 zvezde. Najsjanija je Polaris A, [[Cefeida]] [[HR dijagram|-{F7}-]] klase. Oko Polarisa A orbitiraju druge dve zvezde – bliža Polaris -{Ab}- i dalja Polaris -{B}-.
Zvezda severnjača predstavlja sistem sastavljen od 3 zvezde. Najsjanija je Polaris A, [[Cefeida]] [[HR dijagram|-{F7}-]] klase. Oko Polarisa A orbitiraju druge dve zvezde – bliža Polaris -{Ab}- i dalja Polaris -{B}-.


Ред 15: Ред 177:


Međutim, kako Severnjača nije uvek bila ovako blizu seversnog pola, radi preciznije orijentacije određivan je i položaj β i γ Malog medveda ([[Kohab]] i [[Ferkad]]). Radi lakšeg izvođenja korekcije, konstruisano je nekoliko instrumenata ([[Kortezov rog]], [[nokturnal]], [[polarni teleskop]]).
Međutim, kako Severnjača nije uvek bila ovako blizu seversnog pola, radi preciznije orijentacije određivan je i položaj β i γ Malog medveda ([[Kohab]] i [[Ferkad]]). Radi lakšeg izvođenja korekcije, konstruisano je nekoliko instrumenata ([[Kortezov rog]], [[nokturnal]], [[polarni teleskop]]).

== Zvezdani sistem ==

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/> 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
| title=An Anthology of Visual Double Stars
| display-authors=1 | first1=Bob | last1=Argyle
| first2=Mike | last2=Swan | first3=Andrew | last3=James
| date=August 29, 2019 | page=265 | isbn=9781108601702
| publisher=Cambridge University Press
| url=https://www.google.com/books/edition/An_Anthology_of_Visual_Double_Stars/jSmqDwAAQBAJ?gbpv=1&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/>

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
| title=On the variable velocity of Polaris in the line of sight
| last=Campbell | first=W. W.
| journal=Publications of the Astronomical Society of the Pacific
| volume=11 | pages=195–199| date=October 1899
| doi=10.1086/121339 | bibcode=1899PASP...11..195C
}}</ref> Since Polaris A is a known cepheid variable, [[Joseph Haines Moore|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 [[stellar pulsation|pulsation]] period combined with a much longer [[orbital period]] and a large [[orbital eccentricity|eccentricity]] of around 0.6.<ref>{{cite journal
| title=Note on the Longitude of the Lick Observatory
| last=Moore | first=J. H.
| journal=Publications of the Astronomical Society of the Pacific
| volume=39 | issue=230 | page=249 | date=August 1927
| doi=10.1086/123734 | bibcode=1927PASP...39..249M
}}</ref> 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 [[Boris Gerasimovich|B. P. Gerasimovič]] in 1939.<ref name=Roemer1965>{{citation
| title=Orbital Motion of Alpha Ursae Minoris from Radial Velocities
| last=Roemer | first=Elizabeth
| journal=Astrophysical Journal
| volume=141 | page=1415 | date=May 1965
| doi=10.1086/148230 | bibcode=1965ApJ...141.1415R
}}</ref>

As part of her doctoral thesis, in 1955 [[Elizabeth Roemer|E. Roemer]] used radial velocity data to derive an orbital period of 30.46&nbsp;y for the Polaris A system, with an eccentricity of 0.64.<ref>{{citation
| title=Parallax and orbital motion of spectroscopic binary Polaris from photographs taken with the 24-inch Sproul refractor.
| last=Wyller | first=A. A.
| journal=Astronomical Journal
| volume=62 | pages=389–393 | date=December 1957
| doi=10.1086/107559 | bibcode=1957AJ.....62..389W }}</ref> [[Karl Walter Kamper|K. W. Kamper]] in 1996 produced refined elements with a period of {{val|29.59|0.02|u=years}} and an eccentricity of {{val|0.608|0.005}}.<ref name=Kamper1996>{{cite journal
| title=Polaris Today
| last=Kamper | first=Karl W.
| journal=Journal of the Royal Astronomical Society of Canada
| volume=90 | page=140 | date=June 1996
| bibcode=1996JRASC..90..140K }}</ref> In 2019, a study by R. I. Anderson gave a period of {{val|29.32|0.11|u=years}} with an eccentricity of {{val|0.620|0.008}}.<ref name=Anderson2019>{{cite journal
| title=Probing Polaris' puzzling radial velocity signals. Pulsational (in-)stability, orbital motion, and bisector variations
| last=Anderson | first=R. I.
| journal=Astronomy & Astrophysics
| volume=623 | id=A146 | pages=17 | date=March 2019
| doi=10.1051/0004-6361/201834703 | arxiv=1902.08031
| bibcode=2019A&A...623A.146A | s2cid=119467242 }}</ref>

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.<ref name=Wielen/><ref>{{cite journal|bibcode=2010AJ....139.1968E|title=Chandra Observation of Polaris: Census of Low-mass Companions|journal=The Astronomical Journal|volume=139|issue=5|pages=1968|last1=Evans|first1=Nancy Remage|last2=Guinan|first2=Edward|last3=Engle|first3=Scott|last4=Wolk|first4=Scott J.|last5=Schlegel|first5=Eric|last6=Mason|first6=Brian D.|last7=Karovska|first7=Margarita|last8=Spitzbart|first8=Bradley|year=2010|doi=10.1088/0004-6256/139/5/1968|doi-access=free}}</ref>


== Vidi još ==
== Vidi još ==
Ред 21: Ред 234:
* [[Navigacija]]
* [[Navigacija]]
* [[Precesija]]
* [[Precesija]]

== Reference ==
{{Reflist|refs=
<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="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>

<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=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>

}}


== Spoljašnje veze ==
== Spoljašnje veze ==

Верзија на датум 15. јун 2022. у 23:50

Polaris
Chart showing star positions and boundaries of the Ursa Minor constellation
Polaris (α Ursae Minoris, circled in red) in the constellation Ursa Minor (white area)
Opservacioni podaci
Epoha J2000      Ravnodnevnica
Sazvežđe Ursa Minor
Izgovor /pəˈlɛərɪs, -ˈlær-/;
UK: /pəˈlɑːrɪs/[1]
α UMi Aa
Rektascenzija 02h 31m 49.09s
Deklinacija +89° 15′ 50.8″
Prividna magnituda (V) 1.98[2] (variable 1.86–2.13)
α UMi Ab
Rektascenzija
Deklinacija
Prividna magnituda (V) 9.2[2]
α UMi B
Rektascenzija 02h 30m 41.63s
Deklinacija +89° 15′ 38.1″
Prividna magnituda (V) 8.7[2]
Karakteristike
α UMi Aa
Spektralni tip F7Ib[3]
U−B indeks boja 0.38[2]
B−V indeks boja 0.60[2]
Varijabilni tip Classical Cepheid[4]
α UMi Ab
Spektralni tip F6V[2]
α UMi B
Spektralni tip F3V[2]
U−B indeks boja 0.01[5]
B−V indeks boja 0.42[5]
Astrometrija
Radijalna brzina (Rv)−17 km/s
Sopstveno kretanje (μ) RA: 198.8±0.20 mas/g
Dek.: -15±0.30 mas/g
Paralaksa (π)7.54 ± 0.11[6] mas
Rastojanje323–433[7] sg
(99–133[7] pf)
Apsolutna magnituda (MV)−3.6 (α UMi Aa)[2]
3.6 (α UMi Ab)[2]
3.1 (α UMi B)[2]
Orbita[8]
Primarnaα UMi Aa
Kompanjonα UMi Ab
Period (P)29.59 ± 0.02 g
Velika poluosa (a)0.1204 ± 0.0059"
(≥2,90±0,03 AU[9])
Ekscentricitet (e)0.608 ± 0.005
Inklinacija (i)146.2 ± 10.9°
Longituda uzlaznog čvora (Ω)191.4 ± 4.9°
Apsidna epoha (T)1987.66 ± 0.13
Argument perihela (ω)
(sekundarni)		123.01 ± 0.75°
Poluamplituda (K1)
(primarna)		3.72 ± 0.03 km/s
Detalji
α UMi Aa
Masa5.4[10] M☉
Poluprečnik37.5[10] R☉
Luminoznost (bolometrijska)1,260[10] L☉
Površinska gravitacija (log g)2.2[11] cgs
Temperatura6015[5] K
Metaličnost112% solar[12]
Rotacija119 days[3]
Rotaciona brzina (v sin i)14[3] km/s
Starost70[13] Myr
α UMi Ab
Masa1.26[2] M☉
Poluprečnik1.04[2] R☉
Luminoznost (bolometrijska)3[2] L☉
Starost70[13] Myr
α UMi B
Masa1.39[2] M☉
Poluprečnik1.38[5] R☉
Luminoznost (bolometrijska)3.9[5] L☉
Površinska gravitacija (log g)4.3[5] cgs
Temperatura6900[5] K
Rotaciona brzina (v sin i)110[5] km/s
Pozicija (relativno na α UMi Aa)
Komponentaα UMi Ab
Epoha posmatranja2005.5880
Ugaona udaljenost0.172″
Ugao položaja231.4°
Pozicija (relativno na α UMi Aa)
Komponentaα UMi B
Epoha posmatranja2005.5880
Ugaona udaljenost18.217″
Ugao položaja230.540°
Druge oznake
Polaris, North Star, Cynosura, Alruccabah, Phoenice, Navigatoria, Star of Arcady, Yilduz, Mismar, Alpha UMi, α UMi, 1 Ursae Minoris, BD+88° 8, FK5 907, GC 2243, HD 8890, HIP 11767, HR 424, SAO 308, ADS 1477, CCDM J02319+8915
Referentne baze podataka
SIMBADα UMi A
α UMi B

Zvezda severnjača (lat. Polaris) je zvezda najbliža severnom nebeskom polu Zemlje (2006 godine je bila udaljena od njega 42').[14] Najsjanija je zvezda sazvežđa Mali medved (relativna magnituda 1,97), pa nosi i oznaku α Ursa Minoris (αUMi). Vidi se samo sa severne hemisfere, na kojoj je i cirkumpolarna. Zahvaljujući svom položaju na noćnom nebu kao i relativno lakoj uočljivosti, koristi se za orijentaciju. Od Zemlje je udaljena 430±30 svetlosnih godina.

Komponente sistema

Severnjača i sazvežđe Velikog i Malog medveda (levo). Komponente sistema snimljene Habl svemirskim teleskopom (desno).

Zvezda severnjača predstavlja sistem sastavljen od 3 zvezde. Najsjanija je Polaris A, Cefeida F7 klase. Oko Polarisa A orbitiraju druge dve zvezde – bliža Polaris Ab i dalja Polaris B.

Polaris B je F3V klase i pripada glavnom nizu. Kreće se na oko 2400 AJ oko Polarisa A, tako da se može videti i relativno malim teleskopima. Otkrio ju je Vilhelm Heršel 1780. godine.

Postojanje Polarisa Ab je pretpostavljeno 1929. godine analizom spektra Polarisa A, a potvrđeno je 2006. nakon što je svemirski teleskop „Habl“ snimio sve tri komponente sistema. Polaris Ab se kreće na svega 18,5 AJ oko Polarisa A, zbog čega ju je teško razlučiti.

Novija istraživanja sugerišu da je ovaj trojni sistem zapravo deo razvejanog otvorenog zvezdanog jata sastavljenog od zvezda klasa A i F.

Upotreba za orijentaciju

Severnjača je trenutno zvezda (odnosno zvezdani sistem) najbliža severnom nebeskom polu, zbog čega se može koristiti za orijantaciju. Severnjača rotira oko nebeskog pola po krugu prečnika 1°,5. Zbog precesije, zvezda koja pokazuje sever menja se kroz vreme, tako da je upotreba αUMi kao severnjače počela početkom nove ere i moći će se koristiti u tu svrhu još oko 2000 godina.

Međutim, kako Severnjača nije uvek bila ovako blizu seversnog pola, radi preciznije orijentacije određivan je i položaj β i γ Malog medveda (Kohab i Ferkad). Radi lakšeg izvođenja korekcije, konstruisano je nekoliko instrumenata (Kortezov rog, nokturnal, polarni teleskop).

Zvezdani sistem

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),[13] and Polaris Ab (or P), a very close F6 main-sequence star with a mass of 1.26 M☉.[2] Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a reflecting telescope of his own,[15] 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.[16][17]

The variable radial velocity of Polaris A was reported by W. W. Campbell in 1899, which suggested this star is a binary system.[18] 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.[19] 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.[20]

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.[21] 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.[22] 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.[9]

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.[13][23]

Vidi još

Reference

  1. ^ „Polaris | meaning in the Cambridge English Dictionary”. Cambridge English Dictionary. Приступљено 11. 12. 2020. 
  2. ^ а б в г д ђ е ж з и ј к л љ м 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. Bibcode:2008AJ....136.1137E. S2CID 16966094. arXiv:0806.4904 Слободан приступ. doi:10.1088/0004-6256/136/3/1137. 
  3. ^ а б в 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. Bibcode:2008AJ....135.2240L. S2CID 12176373. arXiv:0804.2793 Слободан приступ. doi:10.1088/0004-6256/135/6/2240. 
  4. ^ Samus, N. N.; Kazarovets, E. V.; et al. (2017). „General Catalogue of Variable Stars”. Astronomy Reports. 5.1. 61 (1): 80—88. Bibcode:2017ARep...61...80S. S2CID 125853869. doi:10.1134/S1063772917010085. 
  5. ^ а б в г д ђ е ж 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. Bibcode:2008MNRAS.387L...1U. S2CID 18848139. arXiv:0708.0333 Слободан приступ. doi:10.1111/j.1745-3933.2008.00426.x. 
  6. ^ Van Leeuwen, F. (2007). „Validation of the new Hipparcos reduction”. Astronomy and Astrophysics. 474 (2): 653—664. Bibcode:2007A&A...474..653V. S2CID 18759600. arXiv:0708.1752 Слободан приступ. doi:10.1051/0004-6361:20078357. 
  7. ^ а б 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. Bibcode:2013ApJ...762L...8T. S2CID 119245441. arXiv:1211.6103 Слободан приступ. doi:10.1088/2041-8205/762/1/L8. 
  8. ^ 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. Bibcode:2018ApJ...863..187E. S2CID 119392532. arXiv:1807.06115 Слободан приступ. doi:10.3847/1538-4357/aad410. 
  9. ^ а б Anderson, R. I. (март 2019). „Probing Polaris' puzzling radial velocity signals. Pulsational (in-)stability, orbital motion, and bisector variations”. Astronomy & Astrophysics. 623: 17. Bibcode:2019A&A...623A.146A. S2CID 119467242. arXiv:1902.08031 Слободан приступ. doi:10.1051/0004-6361/201834703. A146. 
  10. ^ а б в Fadeyev, Y. A. (2015). „Evolutionary status of Polaris”. Monthly Notices of the Royal Astronomical Society. 449 (1): 1011—1017. Bibcode:2015MNRAS.449.1011F. S2CID 118517157. arXiv:1502.06463 Слободан приступ. doi:10.1093/mnras/stv412. 
  11. ^ 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. Bibcode:2005MNRAS.362.1219U. doi:10.1111/j.1365-2966.2005.09353.x Слободан приступ. 
  12. ^ 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. Bibcode:2001A&A...373..159C. S2CID 17519049. arXiv:astro-ph/0106438 Слободан приступ. doi:10.1051/0004-6361:20010525. 
  13. ^ а б в г Wielen, R.; Jahreiß, H.; Dettbarn, C.; Lenhardt, H.; Schwan, H. (2000). „Polaris: Astrometric orbit, position, and proper motion”. Astronomy and Astrophysics. 360: 399. Bibcode:2000A&A...360..399W. arXiv:astro-ph/0002406 Слободан приступ. 
  14. ^ Kaler, Jim. „Polaris (Alpha Ursae Minoris)”. Stars. Приступљено 2020-09-09. 
  15. ^ Argyle, Bob; et al. (29. 8. 2019). An Anthology of Visual Double Stars. Cambridge University Press. стр. 265. ISBN 9781108601702. 
  16. ^ „There's More to the North Star Than Meets the Eye”. Hubblesite.org. 2006-01-09. Приступљено 2020-02-27. 
  17. ^ Evans, N. R.; Sasselov, D. D.; Short, C. I. (2002). „Polaris: Amplitude, Period Change, and Companions”. The Astrophysical Journal. 567 (2): 1121. Bibcode:2002ApJ...567.1121E. doi:10.1086/338583 Слободан приступ. 
  18. ^ Campbell, W. W. (октобар 1899). „On the variable velocity of Polaris in the line of sight”. Publications of the Astronomical Society of the Pacific. 11: 195—199. Bibcode:1899PASP...11..195C. doi:10.1086/121339. 
  19. ^ Moore, J. H. (август 1927). „Note on the Longitude of the Lick Observatory”. Publications of the Astronomical Society of the Pacific. 39 (230): 249. Bibcode:1927PASP...39..249M. doi:10.1086/123734. 
  20. ^ Roemer, Elizabeth (мај 1965), „Orbital Motion of Alpha Ursae Minoris from Radial Velocities”, Astrophysical Journal, 141: 1415, Bibcode:1965ApJ...141.1415R, doi:10.1086/148230 
  21. ^ Wyller, A. A. (децембар 1957), „Parallax and orbital motion of spectroscopic binary Polaris from photographs taken with the 24-inch Sproul refractor.”, Astronomical Journal, 62: 389—393, Bibcode:1957AJ.....62..389W, doi:10.1086/107559 
  22. ^ Kamper, Karl W. (јун 1996). „Polaris Today”. Journal of the Royal Astronomical Society of Canada. 90: 140. Bibcode:1996JRASC..90..140K. 
  23. ^ 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. Bibcode:2010AJ....139.1968E. doi:10.1088/0004-6256/139/5/1968 Слободан приступ. 

Spoljašnje veze

Mediji vezani za članak Zvezda severnjača na Vikimedijinoj ostavi

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