Mu Herculis

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Our Sun rings like a bell. Sound waves travel through the Sun's interior, causing its surface to rise and fall just a little bit. Astronomers have measured similar quakes in the surfaces of several other stars, including one in the constellation Hercules.

Mu Herculis is bright enough to see with the unaided eye, but faint enough that you'll need a star chart to pick it out from its mates in Hercules. It rises around nightfall and climbs high across the sky later on.

Mu Herculis is only 27 light-years away, so it's one of our closer neighbors. It's similar to the Sun -- it has nearly the same temperature and color -- but it's in a more advanced stage of life.

The Sun generates energy by converting hydrogen into helium at its center. But Mu Herculis has consumed so much of the hydrogen at its center that it can no longer generate nuclear reactions there. Instead, it shines by burning hydrogen in a layer around the center.

This change has caused the star to expand and brighten, so it's about three times brighter than the Sun. It's what astronomers call a subgiant. Eventually, it'll become a red giant, so it'll be even bigger and brighter, but a good bit cooler.

Recently, astronomers discovered that Mu Herculis oscillates just like the Sun does. And just as earthquakes help geologists probe the interior of Earth, the "starquakes" in Mu Herculis will help astronomers investigate the interior of this nearby star.

Script by Ken Croswell, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.