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The Question

(Submitted February 02, 1998)

I have a couple of questions for you on binary stars. I would just like to know how the stars got their name "Binary," which scientist discovered them, and why people find them so interesting.

The Answer

'Binary' just means having two parts, and you will find it used in many places (whenever there are two of something) and not just in connection with stars. The English astronomer William Herschel coined the term binary star, after an investigation in the 1790s of stars that appear close together in the sky showed that many were indeed pairs of stars traveling together. Binary stars are very important in astronomy, because a lot of things which are hard to discover when stars are on their own can be easily measured when two are together. When two things are close together, the effect each other in many ways, and we can learn a lot from those effects. For example, two stars close together exert a gravitational pull on each other changing the way they move. By measuring their movements very carefully we can often figure out how much material is in each star - how heavy it is.

Paul Butterworth
for the Ask an Astrophysicist team

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