Editing Thuban

{{Short description|Star in the constellation of Draco}}
{{About|the star|AMD's Thuban processor core|Phenom II}}
{{Starbox begin}}
{{Starbox image
 | image=
{{Location mark
|image=Draco constellation map.svg|alt=|float=center|width=260
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=Thuban
|x=828|y=622
}}
|caption=Location of Thuban (circled)
}}
{{Starbox observe
 |epoch=J2000
 | ra={{RA|14|04|23.3500}}<ref name=hipparcos/>
 | dec={{DEC|+64|22|33.062}}<ref name=hipparcos/>
 | appmag_v=3.67<ref name=Anderson_Francis_2012>{{cite journal| last1=Anderson | first1=E. | last2=Francis | first2=Ch. | title=XHIP: An extended hipparcos compilation | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | arxiv=1108.4971 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref>
 | constell=[[Draco (constellation)|Draco]]
}}
{{Starbox character
 | class=A0IV + A1V<ref name=Pavlovski/>
 | b-v={{val|−0.049|0.005}}<ref name=Anderson_Francis_2012/>
 | u-b=−0.08
 | variable=suspected [[Maia variable|Maia]]<ref name=kallinger>{{Cite journal | doi = 10.1017/S1743921305009865| title = The puzzling Maia candidate star α Draconis| year = 2005| last1 = Kallinger | first1 = T. | last2 = Iliev | first2 = I.| last3 = Lehmann | first3 = H.| last4 = Weiss | first4 = W. W. | journal = Proceedings of the International Astronomical Union| volume = 2004| pages = 848–852| bibcode = 2004IAUS..224..848K| doi-access = free}}</ref>
}}
{{Starbox astrometry
 | radial_v=−13.0
 | prop_mo_ra=−56.34<ref name=hipparcos/>
 | prop_mo_dec= 17.21<ref name=hipparcos/>
 | gal_lat=+50.9588
 | gal_lon=110.5237
 | parallax=10.76
 | p_error=0.17
 |parallax_footnote=<ref name=hipparcos>{{cite journal|bibcode=2007A&A...474..653V|title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|last1=Van Leeuwen|first1=F.|year=2007|doi=10.1051/0004-6361:20078357|arxiv = 0708.1752 |s2cid=18759600}}</ref>
 |absmag_v=−1.20<ref name=murphy>{{cite journal|bibcode=2017MNRAS.466..546M|arxiv=1612.01528|title=Gaia's view of the λ Boo star puzzle|journal=Monthly Notices of the Royal Astronomical Society|volume=466|issue=1|pages=546|last1=Murphy|first1=Simon J.|last2=Paunzen|first2=Ernst|year=2017|doi=10.1093/mnras/stw3141|doi-access=free |s2cid=119328659}}</ref>
}}
{{Starbox orbit
| reference = <ref name=Pavlovski>{{cite journal|doi=10.1051/0004-6361/202142292|title=Dynamical parallax, physical parameters, and evolutionary status of the components of the bright eclipsing binary α Draconis|year=2022|last1=Pavlovski|first1=K.|last2=Hummel|first2=C. A.|last3=Tkachenko|first3=A.|last4=Dervişoğlu|first4=A.|last5=Kayhan|first5=C.|last6=Zavala|first6=R. T.|last7=Hutter|first7=D. J.|last8=Tycner|first8=C.|last9=Şahin|first9=T.|last10=Audenaert|first10=J.|last11=Baeyens|first11=R.|last12=Bodensteiner|first12=J.|last13=Bowman|first13=D. M.|last14=Gebruers|first14=S.|last15=Jannsen|first15=N. E.|last16=Mombarg|first16=J. S. G.|journal=Astronomy & Astrophysics|volume=658|pages=A92|arxiv=2111.03887|bibcode=2022A&A...658A..92P|s2cid=243847585}}</ref>
| period_unitless = 51.417350 d
| periastron = JD&nbsp;2453498.8
| eccentricity = 0.43
| periarg = 22.4
| node = 252.6
| inclination = 85.4
| axis_unitless = 5.52 mas
| k1 = 48.512
| k2 = 63.58
}}
{{Starbox detail
| source = <ref name=Pavlovski/>
| component1 = α Draconis A<br />Alpha Draconis A
| mass = 3.186
| radius = 4.932
| gravity = 3.555
| temperature = 10225
| luminosity = 240<!-- log(L) = 2.380 -->
| rotational_velocity = 25.4
| age_myr = 280
| component2 = α Draconis B<br />Alpha Draconis B
| mass2 = 2.431
| radius2 = 2.326
| gravity2 = 4.090
| temperature2 = 9930
| luminosity2 = 47.5<!-- log(L) = 1.677 -->
| rotational_velocity2 = 168
| age_myr2 = 345
}}
{{Starbox catalog
| names= {{odlist | B=Alpha Dra, α Dra | GSC=04174-01262 | 2MASS=J14042335+6422331 | F=11&nbsp;Dra | HD=123299 | AG=+64°666 | PLX=3209 | TYC=4174-1262-1 | BD=+65°978 | FK5=521 | HIP=68756 | PPM=18861 | GC=19019 | HR=5291 | IRAS=14030+6436 | SAO=16273 }}
}}
{{Starbox reference |
  Simbad=Alpha+Draconis
}}
{{Starbox end
}}

'''Thuban''' ({{IPAc-en|'|θj|uː|b|æ|n}}),<ref name=Kunitzsch>{{cite book
 |last1=Kunitzsch |first1=Paul
 |last2=Smart |first2=Tim
 |date = 2006 |edition = 2nd rev.
 |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
 |publisher = Sky Pub |location = Cambridge, Massachusetts
 |isbn = 978-1-931559-44-7
}}</ref> with [[Bayer designation]] '''Alpha Draconis''' or '''α Draconis''', is a [[binary star]] system in the [[Northern celestial hemisphere|northern]] [[constellation]] of [[Draco (constellation)|Draco]]. A relatively inconspicuous star in the night sky of the [[Northern Hemisphere]], it is historically significant as having been the north [[pole star]] from the 4th to 2nd millennium BC.

[[Johann Bayer]] gave Thuban the designation [[Alpha]] and placed it as the only member of his ''secundae'' magnitude class in Draco, although its current [[apparent magnitude]] of 3.65 means it is 3.7 times fainter than the brightest star in the constellation, [[Gamma Draconis]] (Eltanin), which Bayer placed in his ''tertiae'' magnitude class although its current apparent magnitude is 2.24.<ref name="Bayer1603">{{cite book|author=Johann Bayer|title=Uranometria: Omnivm Asterismorvm Continens Schemata, Nova Methodo Delineata, Aereis Laminis Expressa|url=https://books.google.com/books?id=ivZeAAAAcAAJ|year=1603}}</ref>

==Nomenclature==
''α Draconis'' ([[Latinisation of names|Latinised]] to ''Alpha Draconis'') is the star's [[Bayer designation]].

The traditional name ''Thuban'' is derived from the [[Arabic]] word {{lang|ar|ثعبان}} ''{{Transliteration|ar|DIN|thuʿbān}}'' ('large snake' (e.g. a python or a legendary draconian serpent)). It is sometimes known as the ''Dragon's Tail'' and as ''Adib'' {{IPAc-en|@|'|d|iː|b}}.<ref name=Kunitzsch/> In 2016, the [[International Astronomical Union]] organized a [[Working Group on Star Names]] (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|access-date=22 May 2016}}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref> included a table of the first two batches of names approved by the WGSN; which included ''Thuban'' for this star. It is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref>

In [[Chinese astronomy|Chinese]], {{lang|zh|紫微右垣}} ({{lang|zh-Latn|Zǐ Wēi Yòu Yuán}}), meaning ''[[Purple Forbidden enclosure|Right Wall of Purple Forbidden Enclosure]]'', refers to an [[Asterism (astronomy)|asterism]] consisting of Alpha Draconis, [[Kappa Draconis]], [[Lambda Draconis]], [[24 Ursae Majoris]], [[43 Camelopardalis]], [[Alpha Camelopardalis]] and [[BK Camelopardalis]].<ref>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref> Consequently, the [[Chinese star name|Chinese name]] for Alpha Draconis itself is {{lang|zh|紫微右垣一}} ({{lang|zh-Latn|Zǐ Wēi Yòu Yuán yī}}, {{langx|en|the First Star of Right Wall of Purple Forbidden Enclosure}}),<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20100819122914/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm |date=2010-08-19 }}, Hong Kong Space Museum. Retrieved 2010-11-23.</ref> representing {{lang|zh|右樞}} ({{lang|zh-Latn|Yòushū}}), meaning ''Right Pivot''.<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm#PrupleForbiddenEnclosure English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name] {{webarchive|url=https://web.archive.org/web/20100810114313/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm |date=2010-08-10 }}, Hong Kong Space Museum. Retrieved 2010-11-23.</ref>

== Visibility ==
Given good viewing conditions, Thuban is relatively easy to spot in the night sky, due to its location in relation to the [[Big Dipper]] (aka the Plough) [[Asterism (astronomy)|asterism]] of [[Ursa Major]]. While it is well known that the two outer stars of the 'dipper' point to the modern-day [[pole star]] [[Polaris]], it is less well known that the two inner stars, [[Phecda]] and [[Megrez]], point to Thuban, just 15 degrees of arc from Megrez. Thuban is not bright enough to be viewed from badly [[light pollution|light-polluted]] areas.

=== Pole star ===
[[File:Precession N.gif|thumb|left|Precession of the equinoxes for the Pole Star. Thuban is toward the right of the image, below the −2000 mark.]]
Due to the [[Precession (astronomy)|precession]] of [[Earth]]'s rotational axis, Thuban was the naked-eye star closest to the [[north pole]] from 3942&nbsp;BC, when it superseded [[Tau Herculis]] as the pole star, until 1793&nbsp;BC, when it was superseded by [[Kappa Draconis]]. It was closest to the pole in 2830&nbsp;BC, when it was less than 10&nbsp;[[arcminutes]] away from the pole.<ref name="MOORE">{{Cite book |doi=10.1007/978-1-4471-3613-2 |title=The Observer's Year |year=1998 |last1=Moore |first1=Patrick |isbn=978-3-540-76147-1 |url-access=registration |url=https://archive.org/details/observersyear36600moor}}</ref> It remained within one degree of celestial north for nearly 200 years afterwards, and even 900 years after its closest approach, was just 5° off the pole. Thuban was considered the pole star until about 1800&nbsp;BC, when the much brighter [[Beta Ursae Minoris]] (Kochab) began to approach the pole as well.

Having gradually drifted away from the pole over the last 4800 years, Thuban is now seen in the night sky at a [[declination]] of {{DEC|64|20|45.6}}, [[Right ascension|RA]] {{RA|14|04|33.58}}. After moving nearly 47° off the pole by [[List of future astronomical events#After 10,000 AD|10,000&nbsp;AD]], Thuban will gradually move back toward the north celestial pole. In [[List of future astronomical events#After 10,000 AD|20,346&nbsp;AD]], it will again be the pole star, that year reaching a maximum declination of {{DEC|88|43|17.3}}, at right ascension {{RA|19|08|54.17}}.{{citation needed|date=July 2015}}

{| class="wikitable" style="margin: 1em auto 1em auto; text-align:center;"
! Preceded by
! [[Pole star]]
! Succeeded by
|-
| [[Tau Herculis]]
| c. 3900–1800 BC
| [[Kochab]]
|}

==Binary system==
[[File:AlphaDraLightCurve.png|thumb|left|A [[light curve]] for Thuban, plotted from ''[[Transiting Exoplanet Survey Satellite|TESS]]'' data.<ref name=MAST>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=16 October 2022}}</ref> The main plot shows the entire light curve, and the inset plots show the primary and secondary minima with an expanded scale.]]
Thuban is a single-lined [[spectroscopic binary]]. For a long time, only the primary star could be detected in the [[stellar spectrum|spectrum]]. The radial velocity variations of the stars can be measured and the pair have a somewhat eccentric orbit of 51.4 days.<ref name=Pavlovski/> The secondary is a [[main-sequence star]] slightly cooler than the primary, with an A1 spectral class.<ref name=Pavlovski/>

The secondary star was detected in high spatial resolution observations using the [[Navy Precision Optical Interferometer]]. The secondary star is 1.8 magnitudes (at 700 [[Nanometre|nm]]) fainter than the primary star and was detected at separations ranging from 6.2 to 2.6 [[milliarcseconds]].<ref>{{Cite journal|last1=Hutter|first1=D. J.|last2=Zavala|first2=R. T.|last3=Tycner|first3=C.|last4=Benson|first4=J. A.|last5=Hummel|first5=C. A.|last6=Sanborn|first6=J.|last7=Franz|first7=O. G.|last8=Johnston|first8=K. J.|date=2016-11-01|title=Surveying the Bright Stars by Optical Interferometry. I. A Search for Multiplicity among Stars of Spectral Types F-K|journal=The Astrophysical Journal Supplement Series|volume=227|issue=1|pages=4|doi=10.3847/0067-0049/227/1/4|issn=0067-0049|bibcode=2016ApJS..227....4H|arxiv = 1609.05254 |s2cid=118803592 |doi-access=free }}</ref> Eclipses were detected using data obtained with the [[Transiting Exoplanet Survey Satellite]] (TESS).<ref>{{Cite journal|last1=Bedding|first1=Timothy R.|last2=Hey|first2=Daniel R.|last3=Murphy|first3=Simon J.|date=2019-10-31|title=A Dance with Dragons: TESS Reveals α Draconis is a Detached Eclipsing Binary|journal=Research Notes of the AAS|language=en|volume=3|issue=10|pages=163|doi=10.3847/2515-5172/ab5112|arxiv=1910.12449|bibcode=2019RNAAS...3..163B|s2cid=213224065 |issn=2515-5172 |doi-access=free }}</ref> The presence of eclipses places Thuban into the class of binaries known as [[eclipsing binaries]].<ref name=Pavlovski/>

== Properties ==
[[Image:Alpha Draconis.jpg|right|upright 1.2|thumb|Thuban (α Dra) in optical light]]
Thuban has a [[spectral class]] of A0III, indicating its similarity to [[Vega]] in temperature and [[electromagnetic spectrum|spectrum]], but more [[Luminosity|luminous]] and more massive. It has been used as an MK spectral standard for the A0III type.<ref name=mk>{{Cite journal|bibcode=1978rmsa.book.....M|title=Revised MK Spectral Atlas for stars earlier than the sun|journal=Williams Bay: Yerkes Observatory|last1=Morgan|first1=W. W.|last2=Abt|first2=Helmut A.|last3=Tapscott|first3=J. W.|year=1978}}</ref>

Thuban is not a main-sequence star; it has now ceased [[hydrogen]] [[nuclear fusion|fusion]] in its core. That makes it a white [[giant star]], being 120 times more [[Solar luminosity|luminous than the Sun]]. It is 300 light-years away and its brightness is only decreased by 0.003 of a magnitude by intervening gas and dust.<ref name=murphy/>

==References==
{{Reflist}}

== External links ==
* Jim Kaler's Stars, University of Illinois: [http://stars.astro.illinois.edu/sow/thuban.html THUBAN (Alpha Draconis)]
* NASA's: [http://www-istp.gsfc.nasa.gov/stargaze/Sprecess.htm History of Precession]
* {{not a typo|Crystalinks}}: [http://www.crystalinks.com/precession.html Precession of the Equinoxes]

{{Sky|14|04|23.3498|+|64|22|33.062|310}}
{{Stars of Draco|state=collapsed}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}
{{Pole star}}

<!-- Properties -->

{{DEFAULTSORT:Thuban}}
[[Category:A-type giants]]
[[Category:Suspected variables]]
[[Category:Spectroscopic binaries]]
<!-- Other -->
[[Category:Draco (constellation)]]
[[Category:Bayer objects|Draconis, Alpha]]
[[Category:Durchmusterung objects|BD+65 0978]]
[[Category:Flamsteed objects|Draconis, 11]]
[[Category:Henry Draper Catalogue objects|123299]]
[[Category:Hipparcos objects|068756]]
[[Category:Bright Star Catalogue objects|5291]]
[[Category:Northern pole stars]]
[[Category:Stars with proper names|Thuban]]