Moon and Regulus

Regulus is one of the brightest stars in the night sky, so people have been looking at it since the beginning. And astronomers have been studying it since the invention of the telescope. And it’s quite close — less than 80 light-years away. So you might think that we’ve known all the important details about it for a long time.

You’d be wrong. Astronomers continue to learn about the system. Less than a decade ago, for example, they found that the bright star we see as Regulus has a close companion. That star tells us a lot about the bright star’s history.

The companion is small, faint, and quite close to the bright star, which is known as Regulus A. So it’s impossible to see the companion directly. Instead, astronomers detected it by measuring the system’s individual wavelengths of light. They reveal a slight shift in the star’s motion caused by the gravitational tug of the companion.

The companion is a white dwarf — the tiny corpse of a once-normal star. That star had to be born with more mass than Regulus A, so it aged faster. It puffed up, then dumped much of its outer layers of gas onto Regulus A. That made Regulus A bigger and hotter, and it made the star spin much faster.

That discovery shows that there’s still a lot to learn about the stars — even the ones we think we know well.

Look for Regulus just above the Moon as they climb into view in mid-evening, and a little farther to the right of the Moon at first light tomorrow.

Script by Damond Benningfield