The Moon lines up with the twins of Gemini tonight. Pollux, the brighter of the two, is above the Moon at nightfall. Castor is about the same distance to the upper left of Pollux.

Castor is a family of six stars. Some of them are big and bright, while others are tiny and faint.

As far as we know, Pollux is a single star. But it’s an impressive one. It’s classified as a giant — it’s much bigger and brighter than the Sun. In fact, it’s the closest giant star to the solar system — just 34 light-years away.

Pollux has puffed up because it’s at the end of its normal lifetime. The nuclear reactions in its core have switched over to a new mode. That’s pushed the surrounding layers outward, making Pollux big and bright.

Just because Pollux is a solo star doesn’t mean it’s alone, though — it has at least one planet.

Astronomers at McDonald Observatory found evidence of the planet three decades ago. It was confirmed in 2006.

The planet is about three times the mass of Jupiter, the giant of the solar system. It orbits Pollux once every 19 and a half months.

Scientists called the planet Pollux b. A few years ago, it was assigned a proper name: Thestias. That comes from a Greek name referring to the mother of Pollux. The name hasn’t really caught on yet — it doesn’t show up in scientific papers about the system. But at least it gives science-fiction writers a more lyrical name for the companion of Gemini’s brighter twin.
 

Script by Damond Benningfield

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