Moon and Regulus

Regulus is one of the brightest lights in the night sky. But just how bright depends on how you look at it.

Seen with the eye alone, the heart of the lion ranks as the 21st brightest star in the night. On the astronomical scale, it has a visual magnitude of about 1.4. In this scale, the brighter an object, the lower the number. The brightest star in the night sky, Sirius, has a magnitude of minus 1.4. And the faintest stars visible under a dark sky have a magnitude of about six, which is only about a thousandth as bright as Sirius.

Since the stars are all at different distances from Earth, though, that number doesn’t tell you a star’s true brightness. For that, astronomers calculate its absolute magnitude. That’s how bright the star would look at a distance of 10 parsecs — about 32 light-years.

In this scale, Regulus has a magnitude of point five. So if you lined up Regulus and the Sun at that distance, Regulus would be more than a hundred times brighter.

Even that doesn’t give you the star’s total brightness, because it counts only a star’s visible light. But stars emit many other forms of energy as well. Because Regulus is quite hot, for example, it produces a lot of ultraviolet energy. When you add that to the visible light, the star is about 350 times brighter than the Sun. So Regulus is a brilliant beacon any way you look at it.

And you can get a good look at brilliant Regulus tonight, standing just a whisker away from the Moon.

Script by Damond Benningfield