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Gamma Cephei

September 2, 2012

The constellation Cepheus, the king, circles high across the northern sky on September nights. Its brightest stars form a shape that looks like a child’s drawing of a house, with a square topped by a triangle. It’s upside down during the evening, but turns over as it wheels around the sky during the night.

The star at the top of the roof is actually a system of two stars, plus at least one planet.

Gamma Cephei is 45 light-years away. Its primary star is larger and more massive than the Sun, and farther along in its life cycle. It’s used up the hydrogen in its core, and is now beginning to burn the helium that it created through billions of years of nuclear fusion. As a result, it’s puffing up to form a red giant.

Gamma Cephei’s other star is a red dwarf, which is far smaller, cooler, and less massive than the Sun. Because of its low mass, it will continue to shine for billions of years after its heftier companion expires.

The planet orbits the larger star once every two-and-a-half years. Astronomers discovered it by measuring a tiny “wobble” in the star’s light, which is caused by the planet’s gravitational pull. This technique shows that the planet is at least twice as massive as Jupiter, the largest planet in our own solar system, and perhaps a good bit larger.

Over the last few years, a team has been trying to get a more precise measurement of the planet’s mass, as well as the exact layout of the Gamma Cephei system. They’re using a technique that precisely measures the position of the planet’s parent star in the sky. More about that tomorrow.


Script by Damond Benningfield, Copyright 2012

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