Moon and Regulus

The Moon cozies up to the star Regulus tonight — the bright heart of Leo, the celestial lion. At their closest as viewed from most of the U.S., they’ll be separated by just a whisker.

We see Regulus as a single point of light. But it appears to consist of at least four stars. One of them is big and bright — the only one visible to the eye alone. A second one is a dead star. It’s so faint, and so close to the bright star, that it wasn’t discovered until this century.

The other members of the system are far away from the bright star — roughly 5,000 times the distance between Earth and the Sun. Astronomers deduce that they’re tied to the bright star because they’re the same distance away from us, and they’re moving at the same speed and in the same direction.

The stars haven’t received a lot of attention, though, so we don’t know a whole lot about them. And what is known has a fairly high level of uncertainty.

One thing astronomers are pretty sure of is that the stars form a binary — they’re tied to each other by their gravitational pull. Even so, they’re not close — they’re separated by about 600 times the Earth-Sun distance.

The brighter of the two stars, known as Regulus B, is a little less massive than the Sun, and only about half as bright. The other, Regulus C, is perhaps a third of the Sun’s mass. That makes it only a few percent as bright as the Sun — a feeble companion to the lion’s brilliant heart.

Script by Damond Benningfield