The Sun is 93 million miles away, but that's plenty close to keep us nice and comfortable. But many of the other stars in the galaxy are much hotter and brighter than the Sun, so planets would have to be much farther out to achieve that same level of comfort.
An example is a star known as Zeta Puppis -- Zeta Pup for short. It's the brightest star in the constellation Puppis, which represents the stern of the legendary ship Argo.
Zeta Pup has a couple of claims to fame. One is that it's one of the fastest-moving stars in the galaxy; more about that tomorrow. The other is that it's the hottest star that's visible to the unaided eye: Its surface is more than 60,000 degrees hotter than the Sun's.
Zeta Pup is about 1400 light-years away. But if you lined up Zeta Pup and the Sun at the same distance, Zeta Pup would look about 20,000 times brighter, shining an eyeball-searing blue-white. But because it's so hot, the star actually produces most of its energy not in the form of visible light, but as ultraviolet light. So when you add that in, Zeta Pup actually shines about 750,000 times brighter than the Sun.
If any planets orbit Zeta Pup, they must be a long way out. Anything that was born in a close orbit would have long since been vaporized.
To maintain a comfortable, Earth-like environment, a planet orbiting Zeta Pup would have to be more than 700 times farther out than Earth is from the Sun.
Script by Damond Benningfield, Copyright 2008
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