StarDate: September 8, 2009

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As the year 1992 drew to a close, Czechoslovakia was preparing to split into two countries. Bill Clinton was getting ready to start his first term as president. And light from the star Altair began a journey through space that will end tonight -- when it reaches Earth.

Altair is the brightest star of the constellation Aquila, the eagle. It's high in the southeast at nightfall, forming one of the points of the Summer Triangle. It shines pure white, indicating that it's a good bit hotter than our own star, the Sun.

One reason that Altair looks so bright is that it's close -- a bit less than 17 light-years away. That means that Altair's light takes a bit less than 17 years to reach Earth. So when you look at Altair tonight, you're actually seeing it as it looked almost 17 years ago -- in late 1992.

It's not likely that the star has changed since then, though. Like the Sun, Altair is a sedate star in the prime of its life. It's steadily converting the hydrogen in its core to helium -- a process known as nuclear fusion.

But Altair is almost twice as massive as the Sun. Heavier stars burn through their hydrogen more quickly, so they shine hotter and brighter -- hence Altair's white surface. They also live shorter lives; Altair will live for only around two billion years, compared to more than 10 billion years for the Sun. So our nearby neighbor will pay a price for its showiness.

More about Aquila tomorrow.

Script by Damond Benningfield, Copyright 2009

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