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March 2, 2014

The twins of Gemini — the stars Castor and Pollux — stride boldly across the sky on March evenings. Tonight, they’re high in the east as night falls, not far from Jupiter, the brightest pinpoint of light in the sky at that hour and the largest planet in the solar system.

Pollux is the brighter of Gemini’s twins. In fact, it’s among the 20 brightest stars in the night sky — and the brightest that’s known to have a planet.

Astronomers at McDonald Observatory found evidence of a planet in the early 1990s. They detected a slight back-and-forth “wobble” in the star’s spectrum — the “barcode” that reveals the star’s chemical composition.

One possible explanation for that wobble was the gravitational pull of an orbiting planet. At the time, though, the astronomers couldn’t rule out other possible explanations. But they did rule out the other possibilities and confirm the planet in 2006.

The planet, known as Pollux b, wouldn’t be an especially hospitable place to visit. It’s bigger and heavier than Jupiter, so it’s probably a big ball of gas. And it’s close enough to the star that it’s quite hot. Still, it makes Pollux one of the few bright stars in the night sky with a known planet — a distinction to keep in mind as you watch it swing high across the sky on March evenings.

While Pollux b was discovered through the wobble in Pollux’s light, many other planets have been found with a different technique. More about that tomorrow.


Script by Damond Benningfield, Copyright 2014

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