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When you look into the starry night sky, you're not seeing a true sample of the galaxy's multitude of stars. Instead, most of the stars that are visible to the eye alone are overachievers. They're far brighter than the Sun and the vast majority of the other stars in the galaxy. They're also bigger and hotter than most of the other stars.
A good example is in the constellation Cassiopeia, the queen, which is in the northwest at nightfall. Its brightest stars form an easy-to-spot letter W. Another bright star is just below the lower right point of the W: Zeta Cassiopeia — Zeta Cas for short.
The star is about eight or nine times as massive as the Sun, so its core is tens of millions of degrees hotter than the Sun's. Some of that heat reaches the star's surface, which is tens of thousands of degrees hotter than the Sun.
Zeta Cas is also much bigger than the Sun, so there's a lot more surface area to radiate energy into space. The combination of size and temperature makes Zeta Cas thousands of times brighter than the Sun, so it's easily visible even though it's about 600 light-years away. By comparison, a star like the Sun would fade from view at about 50 light-years.
Stars like Zeta Cas pay a price for their showiness, though. Because their cores are so hot, they burn through their nuclear fuel in a hurry. So while our smaller, cooler Sun will live for about 10 billion years, Zeta Cas will burn out in just 25 million years.
Script by Damond Benningfield, Copyright 2013
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