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September 29, 2015

The range of stars in the universe is tough to grasp. Some are faint cosmic embers, shining just one ten-thousandth as bright as the Sun. Others are eye-searing monsters that are tens of thousands of times brighter than the Sun — and up to hundreds of times bigger.

One example of that variety is the binary system known as Mirach. It forms the second-brightest star in the constellation Andromeda, the princess, which is well up in the east and northeast as night falls.

The system’s main star — the one that’s visible to the unaided eye — is a giant. It’s almost a hundred times wider than the Sun, and almost 2,000 times brighter.

The star is so big because it’s approaching the end of its life. It’s used up the hydrogen fuel in its core, so it’s having to “fuse” other elements to produce energy. The core is smaller than it was originally, but it’s also much hotter. The extra energy pushes on the star’s outer layers, causing them to puff up to giant proportions.

The system’s other star is at least a billion-and-a-half miles away from the giant. And it’s at the opposite end of the size scale. It’s only a fraction the size of the Sun, and only about a third as bright. Unlike its flashier companion, it’s still burning through the original hydrogen in its core. And it’ll keep on doing so for billions of years after the brighter star expires — a faint little star with a long, long lifetime.

We’ll have more about Andromeda tomorrow.


Script by Damond Benningfield, Copyright 2015

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