Cor Caroli

Several bright stars are identified as “hearts.” Regulus, for example, is the heart of the celestial lion, while Antares is the heart of the scorpion. One of the few whose name actually means “the heart” is in good view on spring evenings. Cor Caroli is the brightest star of Canes Venatici, the hunting dogs. It’s in the east as night falls, to the right of the tip of the Big Dipper’s handle.

But the star’s name doesn’t refer to its constellation. Instead, Cor Caroli means “Heart of Charles.” It was named in the 1600s, and it refers to either England’s King Charles I, or his son, Charles II.

Perhaps fittingly, Cor Caroli consists of two stars. One of them is a good bit bigger and heavier than the Sun, and a hundred times brighter. The other also outdoes the Sun, although it’s not as impressive as its sibling.

The brighter star is the prototype of an entire class of stars. They get brighter and fainter over a period of a few days. The change probably is caused by starspots — giant magnetic storms on the star’s surface. They’re darker than the surrounding gas. So as they rotate into view, the star’s overall brightness goes down a bit.

The storms are driven by the star’s high-speed rotation. Despite its great size, it spins once every five-and-a-half days, versus about once a month for the Sun. That stirs up the star’s outer layers of gas, creating a powerful magnetic field — and giving Charles a “stormy” heart.

Script by Damond Benningfield