مختصات: ۰۷ h ۴۵ m ۱۹٫۴ s٬ +۲۸° ۰۱′ ۳۵″
مکان سرپسین در نقشه دوپیکر.
مبدا J۲۰۰۰٫۰ اعتدال J۲۰۰۰٫۰
صورت فلکی دوپیکر
بعد ۰۷ h ۴۵ m ۱۹٫۴ s
میل ۳۵″ ۰۱′ +۲۸°
قدر ظاهری (V) ۱٫۱۵
رده K0IIIb راهنمای رنگ U-B 0٫۸۶
راهنمای رنگ B-V 1٫۰۰ اخترسنجی حرکت مخصوص (μ) RA: −۶۲۵٫۶۹ mas/ yr Dec.: −۴۵٫۹۵ mas/ yr اختلاف منظر (π) ۹۶٫۷۴ ± 0٫۸۷ mas قدر مطلق (M V) ۱٫۰۹
جزئیات جرم ۱٫۸۶ M ☉ شعاع ۸٫۰ R ☉ درخشندگی ۳۲ L ☉ دما ۴٬۸۶۵ K فلزات ۹۰٪ خورشید چرخش ۳۸ روز
SAO ۷۹۶۶۶ منابع سیمباد اطلاعات
سَرپسین یا  رأس پـِیکَر پَسین  (بتا دوپیکر، beta Geminorum، Pollux) درخشانترین ستارهٔ صورت فلکی دوپیکر از قدر ۱/۲ است که سر یکی از دو پیکر را نشان میدهد.
این ستاره، شانزدهمین
ستارهٔ پرنور آسمان است.
صورت فلکی دوپیکر، بهخاطر وجود دوستارهٔ سرپسین و سرپیشین (رأس التوأم مقدم) اینگونه نامیده شدهاست.
جمع سرپسین و سرپیشین را در
پارسی میانه رَخوَت مینامیدند.
↑ مجموعهٔ واژههای مصوّب فرهنگستان زبان فارسی تا پایان سال ۱۳۸۹.
Position of Pollux, in Gemini
Epoch J2000.0 Equinox J2000.0
Right ascension 07 h 45 m 18.94987 s
+28° 01′ 34.3160″
Apparent magnitude (V) 1.14
 Astrometry Radial velocity (R v) +3.23 km/s  Proper motion (μ) RA: –626.55  mas/ yr Dec.: –45.80  mas/ yr Parallax (π) 96.54 ± 0.27  mas Distance 33.78 ± 0.09 ly (10.36 ± 0.03 pc) Absolute magnitude (M V) +1.08 ±0.02 
Details Mass 1.91 ±0.09  M ☉ Radius 8.8 ±0.1  R ☉ Luminosity 43  L ☉ Surface gravity (log g) 2.685 ±0.09  cgs Temperature 4666 ±95  K [Fe/H] Metallicity –0.07 to +0.19  dex Rotation 558 days  Rotational velocity ( v sin i) 2.8 km/s  Age 724  Myr
 Database references SIMBAD data
ARICNS data Pollux , designated  β Geminorum ( Latinised to Beta Geminorum, abbreviated Beta Gem, β Gem), is an orange-hued evolved giant star about 34 light-years from the Sun in the constellation of Gemini. It is the brightest star in Gemini and the closest giant star to the Sun.
Since 1943, the
spectrum of this star has served as one of the stable anchor points by which other stars are classified. In 2006 an  extrasolar planet (designated Pollux b or β Geminorum b, later named Thestias) was confirmed to be orbiting it.
Nomenclature β Geminorum ( Latinised to Beta Geminorum) is the star's Bayer designation.
The traditional name
Pollux refers to the twins Castor and Pollux in Greek and Roman mythology. In 2016, the  International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included  Pollux for this star.
 Castor and Pollux are the two "heavenly twin" stars giving the constellation Gemini ( Latin, 'the twins') its name. The stars, however, are quite different in detail. Castor is a complex sextuple system of hot, bluish-white A-type stars and dim red dwarfs, while Pollux is a single, cooler yellow-orange giant. In Percy Shelley's 1818 poem Homer's Hymn To Castor And Pollux, the star is referred to as "..mild Pollux, void of blame."
Originally the planet was designated Pollux b. In July 2014 the
International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names.  In December 2015, the IAU announced the winning name was Thestias for this planet.  The winning name was based on that originally submitted by  theSkyNet of Australia; namely Leda, Pollux's mother. At the request of the IAU, 'Thestias' (the patronym of Leda, a daughter of Thestius) was substituted. This was because 'Leda' was already attributed to an asteroid and to one of Jupiter's satellites. 
In the catalogue of stars in the
Calendarium of Al Achsasi Al Mouakket, this star was designated Muekher al Dzira, which was translated into Latin as Posterior Brachii, meaning the end in the paw.
Chinese, 北河 ( Běi Hé), meaning , refers to an asterism consisting of Pollux, North River ρ Geminorum, and Castor. Consequently, Pollux itself is known as  北河三 ( Běi Hé sān, English: the Third Star of North River.)
Size comparison of Pollux (left) and The
apparent visual magnitude of 1.14, Pollux is the  brightest star in its constellation, even brighter than its neighbor Castor (α Geminorum). Pollux is 6.7 degrees north of the ecliptic, too far north to be occulted by the moon and planets, but in the distant future it will be close enough.
Parallax measurements by the Hipparcos astrometry satellite  place Pollux at a distance of about 33.78  light-years (10.36 parsecs) from the Sun.
The star is larger than the Sun, with about two
times  its mass and almost nine times its radius. Once an A-type  main sequence star, Pollux has exhausted the hydrogen at its core and  evolved into a giant star with a stellar classification of K0 III. The  effective temperature of this star's outer envelope is about , 4666 K which lies in the range that produces the characteristic orange hue of K-type stars.  Pollux has a  projected rotational velocity of 2.8 km·s. −1 The abundance of elements other than hydrogen and helium, what astronomers term the star's  metallicity, is uncertain, with estimates ranging from 85% to 155% of the Sun's abundance. 
Evidence for a low level of
magnetic activity came from the detection of weak X-ray emission using the ROSAT orbiting telescope. The X-ray emission from this star is about 10 27 erg s −1, which is roughly the same as the X-ray emission from the Sun. A magnetic field with a strength below 1 Gauss has since been confirmed on the surface of Pollux; one of the weakest fields ever detected on a star. The presence of this field suggests that Pollux was once an Ap star with a much stronger magnetic field. The star displays small amplitude  radial velocity variations, but is not photometrically variable.
Since 1993 scientists have suspected an
extrasolar planet orbiting Pollux, from measured  radial velocity oscillations. The existence of the planet, Pollux b, was confirmed and announced on June 16, 2006. Pollux b is calculated to have a mass at least 2.3 times that of Jupiter. The planet is orbiting Pollux with a period of about 590 days.
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Coordinates: 07 h 45 m 19.4 s, 28° 01′ 35″