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Epsilon Aurigae

November 23, 2014

It’s not unusual for a star to change brightness over a period of days, months, or even years. In many cases, such a star is actually a binary — two stars bound by gravity. The stars periodically pass in front of each other, eclipsing some of the system’s light.

But Epsilon Aurigae takes things to the extreme. Its light fades once every 27 years, and the star remains dim for two full years.

The most recent of its eclipses ended in August of 2011. Astronomers kept an eye on it with telescopes on the ground and in space. Their observations helped refine the explanation for this odd system.

Although Epsilon Aurigae is a binary, we see only one of its stars. It’s more than a hundred times wider than the Sun, and tens of thousands of times brighter. The other star is embedded in a cocoon of dust that forms a disk, like a Frisbee. Once every 27 years, the disk passes in front of the bright star, creating a two-year eclipse that cuts the system’s brightness by half.

The star inside the disk is probably heavier than the visible star. It’s blowing a thick “wind” of gas from its surface. Out in space, the atoms cool and stick together to form solid grains, which hide the star from view.

Epsilon Aurigae is in Auriga, the charioteer, which is in the northeast this evening. Look for its brightest star, brilliant Capella. Epsilon Aurigae is close to its right. It’s fairly bright — and will remain so until the next eclipse begins in 2036.


Script by Damond Benningfield, Copyright 2014

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