You might think that astronomers would know just about all there is to know about one of the biggest, brightest stars in our section of the galaxy. That’s not quite the case, though. The star still presents a lot of mysteries.

Deneb is the brightest star in Cygnus, the swan. It’s high in the east-northeast at nightfall, at the northernmost point of the wide Summer Triangle.

Astronomers do know quite a bit about Deneb. They know that it’s about 15 to 20 times as massive as the Sun, and more than a hundred times wider. They know that it’s hotter than the Sun, too. They’ve seen that it pulses in and out a bit, but in an odd way — like a heart in which each chamber cycles to its own beat. And they know that it’s a good ways off, although the exact distance is still a little uncertain.

But there are a lot of things that astronomers don’t know about Deneb.

They don’t know exactly what’s happening in its core, for example. They’re pretty sure that it’s converted its original hydrogen fuel to helium, but they don’t know if it’s burning the helium yet.

They also aren’t sure what’s around the core. It could be a layer of gas made of heavier atoms, which rises and falls like the boiling water in a tea kettle.

And they’re not even sure how fast Deneb turns. Most stars of its class rotate slowly, but Deneb appears to turn faster.

In a way, the questions highlight how modern astronomy works, and we’ll explain how next time — on Star Date.

Script by Damond Benningfield