Pollux (Beta Geminorum)
Pollux (Beta Geminorum) is a star in the constellation Gemini, magnitude 1.1.
The nearest giant star to the Sun — an orange twin that is nothing like its brother Castor.
Castor and Pollux are the heavenly twins of Greek and Roman myth, but the stars are anything but identical. Castor is a family of six stars; Pollux is a single orange giant — the closest giant star to the Sun. It began life as a hot white star rather like Sirius. Having used up the hydrogen in its core, it has swollen to about nine times the Sun’s width, with about twice its mass, and its surface has cooled to about 4,800 K.
In 2006 astronomers announced a planet circling it every 590 days, at least 2.3 times as massive as Jupiter. A public vote named it Thestias. The winning idea was Leda, the twins’ mother, but that name was already taken, so it became Thestias, after her father Thestius. Some doubt remains: the star’s own magnetic activity might mimic the planet’s signal.
Pollux (Beta Geminorum) is 34 light-years away: the light we see from it set off in 1992, around the time the Hubble Space Telescope was launched.
Did you know?
- A whisper of magnetism. Pollux has a magnetic field of under one gauss — one of the weakest ever detected on a star. It may be the faded remnant of a much stronger field from its youth.
- Out of the Moon’s reach. Pollux lies too far north of the Moon’s path to be hidden by it today. The last lunar occultation visible from Earth was on 30 September 117 BC.
- Mild Pollux. In Shelley’s 1818 poem Homer’s Hymn to Castor and Pollux, the star is “mild Pollux, void of blame”.
The brighter of the Gemini twins, a clear orange-yellow beside whiter Castor. Together the two mark the heads of the Twins. Compare their colours side by side — the contrast is easy to see in binoculars.
When and where to see it
It is best placed in the evening sky around February, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere north of 62°S and never sets north of 62°N.
At its highest it stands 68° up from 50°N, 83° up from 35°N, 62° up from the equator, 27° up from 35°S.
Facts
- Type
- Star
- Constellation
- Gemini
- Designations
- Beta Geminorum, β Gem, 78 Gem, HR 2990, HD 62509, HIP 37826
- Magnitude
- 1.1
- Position
- RA 7h 45.3m, Dec +28° 2′ (J2000)
- Spectral type
- K0IIIb
- Colour
- orange (B−V 1.00)
- Distance
- 34 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Pollux (Beta Geminorum) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.