Understanding Spica (Alpha Virginis)

The familiar star Spica (Alpha Virginis) is the fifteenth brightest star in the night sky, in part because it is relatively nearby, only about 250 light-years away. It is easy to find by following the arc of the Big Dipper's handle and using the mnemonic, "Arc to Arcturus (Alpha Bootes) and then spike to Spica." In fact Spica is a "spectroscopic" binary, two stars orbiting each other and too close together to separate visually. They were revealed as being a binary pair in 1890 when spectroscopic...