Pollux is the brightest star in the constellation Gemini and the 17th-brightest star in the night sky. Located approximately 34 light-years from Earth, it is the closest giant star to the Sun and may be orbited by a massive planet whose existence remains debated.
Easy to Find Beside Castor in Gemini
Pollux and Castor form a conspicuous pair marking the heads of Gemini’s celestial twins. From mid-northern latitudes, they are especially prominent on winter and early-spring evenings. To find them, draw an imaginary line from Rigel through Betelgeuse in Orion and continue it roughly three times the distance between those stars. Pollux is the slightly brighter and more golden-orange member of the pair, while Castor appears whiter. Pollux also forms one corner of the Winter Hexagon, alongside Capella, Aldebaran, Rigel, Sirius and Procyon.
The 17th-Brightest Star in the Night Sky
Pollux has an apparent magnitude of approximately 1.14, making it Gemini’s brightest star and one of the brightest stars in the night sky, ranking 17th overall. Curiously, it carries the designation Beta Geminorum, while the slightly fainter Castor is Alpha Geminorum. Bayer letters often reflect brightness, but they were not assigned with complete consistency. Pollux’s prominence is also helped by its proximity, at only 34 light-years from Earth.
Pollux and Castor Are Not Really Twins
Although Pollux and Castor appear close together in our sky, they are not physically connected. Pollux lies approximately 34 light-years from Earth, while Castor is around 51 light-years away, placing the two stars roughly 18 light-years apart in space. They are also very different systems: Pollux is a single orange giant, whereas Castor consists of six stars arranged in three gravitationally bound pairs. Their apparent pairing is simply a line-of-sight effect seen from Earth.
The Closest Giant Star to the Sun
At approximately 34 light-years away, Pollux is the closest giant star to the Sun. It began life as a much hotter blue-white main-sequence star but expanded and cooled after exhausting the hydrogen in its core. Pollux is probably around one billion years old—far younger than the 4.6-billion-year-old Sun—because more massive stars consume their nuclear fuel much more rapidly. Since 1943, Pollux’s spectrum has also served as one of the standard references used to classify other K-type giant stars.
About Nine Times Wider Than the Sun
Pollux has approximately 1.9 times the Sun’s mass but has expanded to around nine times its radius, making the star about 12.5 million kilometers (7.8 million miles) across. Its surface temperature is approximately 4,800 kelvins, compared with about 5,800 kelvins for the Sun, which gives Pollux its orange color. Despite its cooler surface, its much greater size allows it to radiate roughly 40 times as much energy as the Sun.
Destined to Become a White Dwarf
Pollux is not massive enough to end its life as a supernova. As it continues through its stellar life cycle, the star will expand further before eventually shedding its outer layers into space, possibly producing a glowing planetary nebula. Its exposed core will then become a white dwarf—a small, dense stellar remnant that will gradually cool and fade over billions of years.
Its Giant Planet May Not Be a Planet
In 2006, astronomers announced that repeating shifts in Pollux’s spectrum were caused by a giant planet later named Thestias. If the planetary interpretation is correct, Thestias has at least 2.3 times Jupiter’s mass and completes an orbit every 590 days at an average distance of approximately 1.64 astronomical units. However, Pollux appears to rotate over a similarly long period, and magnetic activity on its surface could produce much the same signal. Some catalogues still list Thestias as a planet, but its existence remains disputed.
Pollux Shared His Immortality With Castor
In Greek mythology, Pollux was the immortal son of Zeus, while Castor was the mortal son of King Tyndareus. Despite having different fathers, the brothers were inseparable and were celebrated together as the Dioscuri. After Castor was killed, Pollux begged Zeus not to separate them. Zeus allowed him to share his immortality with his brother, and the pair were ultimately placed among the stars as Gemini—the Twins.