As befits his status as a hero, Perseus strides boldly across the sky this evening. He’s high overhead at nightfall, crowning the sky with a couple of streamers of moderately bright stars. Perseus rescued the princess Andromeda from a nasty sea monster. In one version of the story, he turned the monster to stone by showing him the head of Medusa, one of the Gorgons — monsters in their own right. The names of four of the constellation’s stars are tied to that story. Collectively, they’re known as Gorgonea — the Gorgons. And the most impressive of the four is quite the monster. Gorgonea Tertia — the third Gorgon — is entering the final stage of its life. It converted the original hydrogen fuel in its core to helium, then converted the helium to carbon and oxygen. The core isn’t hot enough to continue the process, though, so it’s no longer generating nuclear reactions. But it is hot enough to push on the layers of gas around it, making the star puff up to enormous proportions. Right now,
