| 词条 | HD 117939 | ||||||||||||||||||||||||||||
| 释义 |
| name = HD 117939 }}{{Starbox observe | epoch=J2000 | ra={{RA|13|34|32.64965}}[1] | dec={{DEC|-38|54|25.9713}}[1] | appmag_v= 7.27[2] | constell=Centaurus }}{{Starbox character | class = G4V[2] | b-v = }}{{Starbox astrometry | prop_mo_ra = 446.17[1] | prop_mo_dec =-394.11[1] | parallax = 33.27 | p_error =0.61 | parallax_footnote =[1] | absmag_v = }}{{Starbox detail | mass = | radius = | gravity = | temperature = 5,730[2] | metal_fe =-0.29[2] | age_gyr = 6.1[2] }}{{Starbox catalog | names = {{odlist|CD=-38° 8635|HD=117939|HIP=66238|GJ=9450|SAO=204606}} }}{{Starbox reference | Simbad = HD+117939 | EPE = | ARICNS = }}{{Starbox end}} HD 117939 is a Sun-like star 98 light years (30.23 parsecs) from the Sun. HD 117939 is a G-type star and a near solar twin, It is much older than the sun at 6.1 billion years, compared to the sun at 4.6 billion years old.[2] HD 117939 is found in the constellation of Centaurus. HD 117939 has an apparent magnitude of 7.291. 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 considered solar twins by the majority of the public. An exact solar twin would be a G2V star with a 5,778K temperature, would be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation.[3] G2V stars with an age of 4.6 billion years are at their most stable state. Proper metallicity and size are also very important to low luminosity variation. [4][5] Sun comparisonChart compares the sun to HD 117939.
See also
References1. ^1 2 3 4 {{cite journal|title=Validation of the new Hipparcos reduction|url=http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...474..653VFUL|author1=van Leeuwen, F.|display-authors=etal|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|date=2007|arxiv=0708.1752|bibcode=2007A&A...474..653V|doi=10.1051/0004-6361:20078357}} {{Stars of Centaurus}}2. ^1 2 3 4 5 {{cite simbad|title=HD 117939|accessdate=2016-09-26 }} 3. ^[https://science.nasa.gov/science-news/science-at-nasa/2013/08jan_sunclimate/ NASA, Science News, Solar Variability and Terrestrial Climate, Jan. 8, 2013] 4. ^University of Nebraska-Lincoln astronomy education group, Stellar Luminosity Calculator 5. ^National Center for Atmospheric Research, The Effects of Solar Variability on Earth's Climate, 2012 Report 6. ^{{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 }} 6 : Henry Draper Catalogue objects|G-type main-sequence stars|Solar analogs|Hipparcos objects|Durchmusterung objects|Gliese and GJ objects |
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