Eclipsing binaries are the most useful, giving us sizes as well as masses of the pair.

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Eclipsing binaries allow us to observe the periodic eclipses of one star by another, which provides us with information on their sizes as well as masses, making them highly useful in astronomy. Eclipsing binaries are useful in determining both the mass and size of the celestial objects involved, making them important tools for astronomers.

Eclipsing Binaries Are the Most Useful, Giving Us Sizes as Well