Moon and Regulus

A bright star with a hint of color stands close above the Moon as darkness falls this evening. That subtle color reveals some important facts about the star.

Regulus is the heart of Leo the lion. It’s actually a system of four stars, but only one is bright enough to see with the eye alone — the star we know as Regulus.

If you look at it carefully, you’ll notice that Regulus shines with just a hint of blue. The color tells us that its surface is much hotter than the surface of the Sun. The hottest stars are bright blue, the coolest are orange or red, and stars in the middle, like the Sun, are yellow.

Regulus is so hot because it’s more than three times as massive as the Sun. That great weight squeezes the star tightly. That makes its core extremely hot, which revs up its nuclear reactions. As a result, Regulus’s lifespan will be billions of years shorter than the Sun’s.

The energy from the core heats the surface, making it blue — and bright. If you placed Regulus and the Sun at the same distance, Regulus would look about 130 times brighter. But because the star’s surface is so hot, it produces much of its energy at ultraviolet wavelengths. When you add that to the visible light, Regulus is about 360 times the Sun’s brightness.

So just from its color, we know that Regulus is hot and heavy, that it will live a short life, and that it produces a lot of ultraviolet energy — a blue-white beacon leading the Moon across tonight’s sky.

Script by Damond Benningfield