Moon and Spica

In astronomy, just because you can’t see something doesn’t mean you can’t study it. That’s the case for a lot of stars. Many systems consist of two or more stars. But in a lot of those systems, one or more stars are hidden from even the biggest telescopes.

A prime example is Spica, the brightest star in Virgo. That bright point is the combined light of two stars. But only one of them is visible.

H.C. Vogel discovered Spica’s dual nature in 1890. He used a spectroscope to break the star’s light into its individual wavelengths. That produced a “barcode” that revealed the star’s temperature, motion, and composition.

Vogel found a second barcode, which was quite faint. It was produced by a companion star.

Detailed study since then has provided details on both stars. The main star is so massive that it will blast itself apart as a supernova. It’s more than 20,000 times brighter than the Sun. The companion is a little less massive, but it’s still more than two thousand times the Sun’s brightness.

The two stars are only about six million miles apart. The smaller, fainter star is so close to the main star that it’s overpowered by the flashier star’s light. So while astronomers have been studying the faint star for more than a century, they’ve never actually seen it.

We can see Spica tonight near the Moon. It climbs up below the Moon by about 9 or 9:30. It’ll be closer to the upper right of the Moon tomorrow night.
 

Script by Damond Benningfield