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Moon and Leo

May 24, 2015

Binary star systems are among an astronomer’s best friends. Measuring the mutual orbit of the two stars reveals the stars’ masses. Comparing the characteristics of the binary stars to individual stars provides good estimates of the masses of those stars. And that, in turn, helps reveal the workings of all stars.

But it can take a while to get the details of a binary system. An example is Algieba, the “forehead” of Leo, the lion. Leo’s brightest star, Regulus, stands above the Moon tonight, with Algieba farther to the upper right of Regulus.

Both of Algieba’s stars are much bigger, brighter, and heavier than the Sun. But some of the details are still unclear. That’s because the stars are a long way apart, so it takes centuries for them to complete one orbit around each other. Astronomers have been plotting that orbit for only around a century, though, which isn’t long enough to lock down the exact timing. And without that, they can’t get the exact masses of Algieba’s stars.

Instead, they have to make some approximations. One of the stars is about twice as massive as the Sun, with the other a bit heavier. Each is a good bit bigger than the Sun, and scores of times brighter, indicating that they’re nearing the ends of their lives. They’re undergoing changes that have made them puff up.

A more precise picture of the system will take a better determination of the star’s masses — something that’ll require many more decades of observations.


Script by Damond Benningfield, Copyright 2015

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