You are here

Moon and Regulus

November 27, 2010

Unlike the Sun, most of the stars in our galaxy have companions. And these twosomes, threesomes, and moresomes come in almost limitless variety. There are big stars and little stars, hot stars and cool stars. Some stars are so close together that they actually touch. And some are so far apart that they look like they’re ignoring each other.

An example of the latter is Regulus, the brightest star of Leo, the lion. It’s to the left of the Moon as they rise around midnight.

The star that we see as Regulus is much larger, brighter, and hotter than the Sun. But it has three companions that are too faint to see with the unaided eye.

One of the companions orbits quite close to Regulus. It’s probably the crushed corpse of a star that was once like Regulus itself.

The other companions form a pair -- they’re tied together by their mutual gravitational pull. But they’re a pretty good distance apart, so it takes almost a millennium for them to orbit each other. Each of them is smaller, fainter, and cooler than the Sun. One of them, in fact, is a dull cosmic ember.

The two stars are also gravitationally bound to Regulus itself. But the ties aren’t that strong, because they’re so far from Regulus that it takes more than a hundred thousand years for them to complete a single orbit.

Even so, as seen from its companions, Regulus would be too bright to look at for long -- a brilliant blue-white companion blazing through the night.

Script by Damond Benningfield, Copyright 2010

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.