{{Short description|Star in the constellation Centaurus}} {{Starbox begin}} {{Starbox observe | epoch = J2000 | constell = [[Centaurus]]<ref name=Anderson_Francis_2012/> | ra = {{RA|13|34|32.64979}}<ref name=GaiaDR3/> | dec = {{DEC|-38|54|25.9678}}<ref name=GaiaDR3/> | appmag_v = 7.29<ref name=Anderson_Francis_2012/> }} {{Starbox character | type = [[Main sequence]]<ref name=GaiaDR3/> | class = G4V<ref name=Gray_et_al_2006/> | b-v = {{val|0.669|0.006}}<ref name=Anderson_Francis_2012/> | u-b = | variable = }} {{Starbox astrometry | radial_v = {{val|+82.23|0.12}}<ref name=GaiaDR3/> | prop_mo_ra = +445.183<ref name=GaiaDR3/> | prop_mo_dec = −393.880<ref name=GaiaDR3/> | parallax = 33.1088 | p_error = 0.0267 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = 4.90<ref name=Anderson_Francis_2012/> }} {{Starbox detail | mass = 0.92<ref name=Fuhrmann_Chini_2019/> | luminosity = 1.00<ref name=tic/> | temperature = 5,690<ref name=tic/> | radius = {{val|1.01|0.04}}<ref name=Fuhrmann_Chini_2019/> | gravity = 4.43<ref name=tic/> | metal_fe = {{val|−0.22|0.07}}<ref name=Fuhrmann_Chini_2019/> | rotation = 2.18 days<ref name=oelkers2018/> | rotational_velocity = {{val|1.0|1.0}}<ref name=Fuhrmann_Chini_2019/> | age_gyr = 6.1<ref name=Porto_de_Mello_et_al_2014/> }} {{Starbox catalog | names = {{odlist | CD=-38°8635 | HD=117939 | HIP=66238 | GJ=9450 | LHS=2760 | SAO=204606 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = HD+117939 }} {{Starbox end}}
'''HD 117939''' is a Sun-like star in the southern [[constellation]] of [[Centaurus]]. With an [[apparent visual magnitude]] of 7.29<ref name=Anderson_Francis_2012/> it is too faint to be viewed with the naked eye, but is within the range of binoculars or a small telescope. It is located at a distance of 98.5 [[light year]]s from the [[Sun]] based on [[stellar parallax|parallax]] measurements, and is drifting further away with a [[radial velocity]] of +82 km/s. This is an intermediate disk<ref name=Fuhrmann_Chini_2019/> star with a high [[proper motion]], traversing the [[celestial sphere]] at an [[angular rate]] of {{val|0.68|u=arcsec yr<sup>−1</sup>}}.<ref name=Bakos_et_al_2002/>
An ordinary [[G-type main-sequence star]] with a [[stellar classification]] of G4V,<ref name=Gray_et_al_2006/> this star is an "excellent [[Photometry (astronomy)|photometric]] match for the Sun";<ref name=Porto_de_Mello_et_al_2014/> the atmospheric properties of the star make it a near [[solar twin]]. It is older than the sun at 6.1 billion years, but is more [[magnetic activity|chromospherically active]].<ref name=Porto_de_Mello_et_al_2014/>
To date no exact solar twin (precisely matching all important properties of the Sun) has been found. However, there are some stars that come very close to being identical to the Sun, and as such are dubbed [[solar twin]]s by astronomers. An exact solar twin would be a 4.6 billion years old G2V star with a 5,772K temperature, the correct metallicity, and a 0.1% [[solar luminosity]] variation.<ref name=NASA_2013/> G2V stars with an age of 4.6 billion years or more have typically reached their most stable state. Proper metallicity and size are also important to low luminosity variation.<ref name=UNL/><ref name=NAP/>
==Sun comparison== Chart compares the sun to HD 117939.
{| class="wikitable" style="text-align: center; white-space: nowrap;" ! Identifier ! [[Stellar classification|Stellar<br>Class]] ! Temperature<br>(K) ! Metallicity<br>(dex) ! Age<br>([[Gigayear|Gyr]]) ! Notes |- |style="text-align:left;"| [[Sun]] | G2V | 5,778 | +0.00 | 4.6 | <ref name=nssdc/> |- |style="text-align:left;"| '''HD 117939''' | G4V | 5,765 | −0.22 | 6.1 | <ref name=Porto_de_Mello_et_al_2014/><ref name=Fuhrmann_Chini_2019/> |}
== See also == * [[List of nearest stars]]
==References== {{Reflist|refs=
<ref name=SIMBAD>{{cite simbad|title=HD 117939|accessdate=2016-09-26 }}</ref>
<ref name=GaiaDR3>{{Cite Gaia DR3|6161806515182527616}}</ref>
<ref name=Anderson_Francis_2012>{{cite XHIP|66238}}</ref>
<ref name=tic>{{cite journal |last1=Stassun |first1=Keivan G. |last2=Oelkers |first2=Ryan J. |last3=Paegert |first3=Martin |last4=Torres |first4=Guillermo |last5=Pepper |first5=Joshua |last6=De Lee |first6=Nathan |last7=Collins |first7=Kevin |last8=Latham |first8=David W. |last9=Muirhead |first9=Philip S. |last10=Chittidi |first10=Jay |last11=Rojas-Ayala |first11=Bárbara |last12=Fleming |first12=Scott W. |last13=Rose |first13=Mark E. |last14=Tenenbaum |first14=Peter |last15=Ting |first15=Eric B. |last16=Kane |first16=Stephen R. |last17=Barclay |first17=Thomas |last18=Bean |first18=Jacob L. |last19=Brassuer |first19=C. E. |last20=Charbonneau |first20=David |last21=Ge |first21=Jian |last22=Lissauer |first22=Jack J. |last23=Mann |first23=Andrew W. |last24=McLean |first24=Brian |last25=Mullally |first25=Susan |last26=Narita |first26=Norio |last27=Plavchan |first27=Peter |last28=Ricker |first28=George R. |last29=Sasselov |first29=Dimitar |last30=Seager |first30=S. |display-authors=1 |title=The Revised TESS Input Catalog and Candidate Target List |journal=The Astronomical Journal |date=2019 |volume=158 |issue=4 |page=138 |doi=10.3847/1538-3881/ab3467 |doi-access=free |arxiv=1905.10694 |bibcode=2019AJ....158..138S }}</ref>
<ref name=oelkers2018>{{cite journal |last1=Oelkers |first1=Ryan J. |last2=Rodriguez |first2=Joseph E. |last3=Stassun |first3=Keivan G. |last4=Pepper |first4=Joshua |last5=Somers |first5=Garrett |last6=Kafka |first6=Stella |last7=Stevens |first7=Daniel J. |last8=Beatty |first8=Thomas G. |last9=Siverd |first9=Robert J. |last10=Lund |first10=Michael B. |last11=Kuhn |first11=Rudolf B. |last12=James |first12=David |last13=Gaudi |first13=B. Scott |title=Variability Properties of Four Million Sources in the TESS Input Catalog Observed with the Kilodegree Extremely Little Telescope Survey |journal=The Astronomical Journal |date=2018 |volume=155 |issue=1 |page=39 |doi=10.3847/1538-3881/aa9bf4 |doi-access=free |arxiv=1711.03608 |bibcode=2018AJ....155...39O }}</ref>
<ref name=Bakos_et_al_2002>{{cite journal | title=Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog | display-authors=1 | last1=Bakos | first1=Gáspár Á. | last2=Sahu | first2=Kailash C. | last3=Németh | first3=Péter | journal=The Astrophysical Journal Supplement Series | volume=141 | issue=1 | pages=187–193 | date=July 2002 | doi=10.1086/340115 | arxiv=astro-ph/0202164 | bibcode=2002ApJS..141..187B | s2cid=36667868 }}</ref>
<ref name=Gray_et_al_2006>{{cite journal | title=Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample | last1=Gray | first1=R. O. | last2=Corbally | first2=C. J. | last3=Garrison | first3=R. F. | last4=McFadden | first4=M. T. | last5=Bubar | first5=E. J. | last6=McGahee | first6=C. E. | last7=O'Donoghue | first7=A. A. | last8=Knox | first8=E. R. | display-authors=1 | journal=[[The Astronomical Journal]] | volume=132 | issue=1 | pages=161–170 | date=July 2006 | doi=10.1086/504637 | arxiv=astro-ph/0603770 | bibcode=2006AJ....132..161G | s2cid=119476992 }}</ref>
<ref name=Fuhrmann_Chini_2019>{{cite journal | title=On ancient solar-type stars | last1=Fuhrmann | first1=Klaus | last2=Chini | first2=Rolf | journal=Monthly Notices of the Royal Astronomical Society | volume=482 | issue=1 | pages=471–489 | date=January 2019 | doi=10.1093/mnras/sty2660 | bibcode=2019MNRAS.482..471F | doi-access=free }}</ref>
<ref name=Porto_de_Mello_et_al_2014>{{cite journal | title=A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun. I. Atmospheric parameters and color similarity to the Sun | last1=Porto de Mello | first1=G. F. | last2=da Silva | first2=R. | last3=da Silva | first3=L. | last4=de Nader | first4=R. V. | display-authors=1 | journal=Astronomy & Astrophysics | volume=563 | id=A52 | pages=25 | date=March 2014 | doi=10.1051/0004-6361/201322277 | arxiv=1312.7571 | bibcode=2014A&A...563A..52P | s2cid=119111150 }}</ref>
<ref name=nssdc>{{cite web | last=Williams | first=D. R. | url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html | title=Sun Fact Sheet | publisher=[[NASA]] | year=2004 | accessdate=2009-06-23 }}</ref>
<ref name=NASA_2013>{{cite web | url=https://science.nasa.gov/science-news/science-at-nasa/2013/08jan_sunclimate/ | publisher=NASA | work=Science News | date=January 8, 2013 | title=Solar Variability and Terrestrial Climate }}</ref>
<ref name=UNL>{{cite web | url=http://astro.unl.edu/classaction/animations/stellarprops/stellarlum.html | publisher=University of Nebraska-Lincoln astronomy education group | title=Stellar Luminosity Calculator }}</ref>
<ref name=NAP>{{cite news | url=http://www.nap.edu/catalog/13519/the-effects-of-solar-variability-on-earths-climate-a-workshop | publisher=National Center for Atmospheric Research | title=The Effects of Solar Variability on Earth's Climate, 2012 Report }}</ref>
}}
{{Stars of Centaurus}} <!-- Properties --> [[Category:G-type main-sequence stars]] [[Category:Solar analogs]] <!-- Other --> [[Category:Centaurus]] [[Category:Durchmusterung objects]] [[Category:Gliese and GJ objects|9450]] [[Category:Henry Draper Catalogue objects|117939]] [[Category:Hipparcos objects|066238]]