Procyon

A star like the Sun is born as a big ball of hot gas. It then spends most of its life getting rid of much of that gas — either in a trickle, or in one giant gasp. The star system known as Procyon contains one star that’s completed that final gasp, and another that’s about to start.

Procyon is the eighth-brightest star in the night sky. Right now, it’s low in the east not long after nightfall. It’s well to the left or upper left of Sirius, the brightest star in the night sky.

The star we see is known as Procyon A. It’s about half-again as massive as the Sun, about twice as wide, and about seven times as bright. Like all stars, it blows a “wind” of hot gas off its surface. Right now, the wind is thin — there’s not a lot to it.

But Procyon A is about to end its “normal” lifetime and enter the next phase — as a giant. Its wind will become much thicker, surrounding the star in a thin cloud. And in a hundred million years or so, it’ll move into the final phase. It’ll expel all of its outer layers of gas over just a few thousand years. That will leave only the star’s dead core — a white dwarf.

That’s already happened to the other star in the system, Procyon B. It was born much heavier than Procyon A, so it aged more quickly. It blew away its outer layers more than a billion years ago. That left Procyon A with a dead companion — and a glimpse into its own future.

Tomorrow: A planet that sprints across the sky.

Script by Damond Benningfield