Seeing Double

High overhead tonight is the majestic lion of the spring sky, Leo. Its "lucida,"or brightest star, is Regulus. The inner stars of the bowl of the Big Dipper point to it.

Regulus, like about half the stars in the sky, is part of a multiple star system. The Regulus star system consists of Regulus itself, a companion star that we can see through binoculars, and a second companion star visible only in large telescopes.

What would it be like to be going around Regulus instead of our own Sun? First of all, Regulus is a lot hotter than the Sun, so to survive we'd have to be about ten times further away from it than we are now from our sun. This would put us about as far away as Saturn is now. Alas, the companion of Regulus is four hundred billion miles away, much further from us than the most distant planet. Since it is a star, it shines by its own light, not by reflected light, like the planets do. It would be bright, but not the brightest star in the sky.

Is it possible for two stars to be so close to each other that an observer on a planet circling one of them would see a sight like two "suns" in the sky? Well, the star W Ursa Majoris, near the Big Dipper, is a double star whose components actually touch each other occasionally. An observer on a planet circling those, if he or she were not incinerated first, would have a really spectacular view.

(03/12/08)