Pollux

Star

Pollux - the brighter of Gemini's twin stars and the nearest giant star to the Sun with a known planet, 33.8 light-years away. An orange giant about nine times the Sun's width, it has swollen and cooled at the end of its life. Its planet, Pollux b (Thestias), is a super-Jupiter on a nearly circular orbit.

Open in 3D viewSee Pollux in the live, interactive 3D map

Key facts

Mass

3.98 × 10³⁰ kg

2 M☉

Radius

6,191,730 km

8.9× wider than the Sun

Surface temperature

4,893 K (4,620 °C)

Luminosity

1.57 × 10²⁸ W

Spectral type

K0III (orange giant)

Science

Physical

Mass: 3.98 × 10³⁰ kg · 2 M☉
Radius: 6,191,730 km · 8.9× wider than the Sun
Density: 4 kg/m³ · 0.004× water; Computed from mass and radius
Spectral type: K0III (orange giant)

Motion through space

Proper motion: 0.628 arcseconds per year · its drift across our sky; SIMBAD — 2007A&A...474..653V, 2018A&A...616A...7S
Radial velocity: +3.4 km/s · moving away from the Sun; SIMBAD — 2007A&A...474..653V, 2018A&A...616A...7S
Speed across our line of sight: 30.8 km/s; Computed from proper motion and parallax
Speed through space, relative to the Sun: 31 km/s; Computed from proper motion, parallax and radial velocity

Rotation

Note: A slowly-rotating giant; its steady, low-amplitude wobble revealed the orbiting planet.

Composition

By mass: An evolved orange giant of about two solar masses that has exhausted its core hydrogen, swelling to some nine times the Sun's width and cooling to an orange glow. It shines about 40 times as bright as the Sun — a preview of what our own star will become in billions of years.

Temperature

Surface: 4,893 K (4,620 °C)

Radiation & temperature

Luminosity: 1.57 × 10²⁸ W · 40.9 L☉
Surface temperature: 4,893 K (4,620 °C)
Peak wavelength: 592 nm · orange light; Computed (Wien's law) from the surface temperature

Discovery & history

Method: Naked-eye star
Name: Its IAU proper name Pollux is one of the mythological Gemini twins (with Castor); it is Beta Geminorum, though in fact the brightest star of Gemini.

Known since antiquity as one of the Gemini twins, Pollux was found in 2006 to host a giant planet from a decades-long radial-velocity wobble tracked at McDonald Observatory - one of the first planets found around a giant star.

Images

Where to find it — in Gemini, the Twins (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image