The Moon has an especially close companion at dawn tomorrow: Spica, the brightest star of Virgo. Depending on your location, they might be separated by as little as the width of a pencil held at arm’s length. And from some parts of the world, the Moon will briefly cover the star.
Spica is a binary – two stars locked in orbit around each other. They’re so close together that we can’t see them as individual stars.
If we could line up the Sun and the system’s main star, Spica A, at the same distance, Spica A would look more than 2,000 times brighter than the Sun. But that’s only part of the story. The surface of Spica A is tens of thousands of degrees hotter than the Sun. Such hot stars produce much of their light in the ultraviolet. If you add that to the equation, Spica A is about 20 thousand times the Sun’s brightness.
The star is so hot because it’s especially heavy – roughly a dozen times the mass of the Sun. Gravity squeezes the star’s core much more tightly than the Sun’s core. That makes the core extremely hot, which revs up its nuclear fusion reactions. Energy from those reactions heats the surrounding layers.
But such massive stars don’t live long. Spica A is only about 12 million years old, compared to four and a half billion years for the Sun. Yet it’s already completed the prime phase of its life. Within a few million years, it’s likely to explode as a supernova – a brilliant demise for a brilliant star.
Script by Damond Benningfield