Moon and Spica

StarDate logo
Moon and Spica

When astronomers look at Spica, they see double. Or at least their instruments do. The system consists of two stars. But they’re so close together that even the biggest telescopes see them as a single point of light. So it took a technique called spectroscopy to “see” the system as a binary.

The technique splits the light from a star into its individual wavelengths. Each chemical element imprints its own “barcode” in that spectrum of light.

In the case of Spica, there are two sets of those barcodes. And they shift back and forth a tiny bit — the result of the orbital motion of the stars around each other.

Careful study of the two spectra has revealed many details about the system.

For example, the main star is much bigger and more massive than the Sun. It’s destined to explode as a supernova. The other star isn’t quite as impressive, but still far more impressive than the Sun. It probably won’t explode, but instead will leave a small but heavy corpse.

The stars orbit each other once every four days. Their surfaces are only a few million miles apart — so close that the gravity of each star distorts the shape of the other — one more amazing finding about this impressive double star.

To the eye alone, Spica looks like a single bright star. Tonight, it’s close to the lower left of the Moon at nightfall. The Moon slides toward it during the night, so they’re especially close as they set, in the wee hours of the morning.

Script by Damond Benningfield

Shopping Cart
Scroll to Top