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Tau Boötis

April 7, 2013

The gap between discovery and knowledge can be a lengthy one. Astronomers have discovered close to a thousand confirmed planets in other star systems, for example. But they’re still filling in the details on many of those planets - a process that can take years.

Consider one of the first exoplanets ever found. Astronomers discovered it in 1996, orbiting Tau Boötis, a fairly bright star in Boötes, the herdsman. And they measured the length of the planet’s “year” - the time it takes to complete one orbit around the star - at about three-and-a-third days. That means the planet is quite close to the star, so it’s quite hot.

But astronomers couldn’t measure the tilt of the planet’s orbit. And without that, they couldn’t measure the planet’s mass, so they couldn’t be sure just what kind of planet it was.

But recent observations by two teams of astronomers have revealed the orbital tilt, and thus the planet’s mass: It’s six times as massive as Jupiter, the largest planet in our own solar system. The finding will help astronomers learn more about the Tau Boötis planet, and about the birth and evolution of all planetary systems.

Under dark skies, Tau Boötis is visible to the eye alone. Look east in early to mid-evening for the bright yellow-orange star Arcturus. Tau Bootis is a few degrees above it. It’s much fainter than Arcturus but it’s worth the effort, because it’s one of the few stars with a known planet that you can see with your own eyes.


Script by Ken Croswell, Copyright 2013

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