Cor Caroli

Dark spots sometimes dot the surface of the Sun – magnetic storms that can last for days or weeks. But the storms on other stars can make those on the Sun look puny. They can be so monstrous that they can change the star’s brightness by quite a bit.

An example is one of the stars of Cor Caroli – the Heart of Charles. As seen by the eye alone, the star is the leading light of Canes Venatici, the hunting dogs. It’s to the right of the handle of the Big Dipper as night falls, and wheels above the dipper later on.

But a closer look shows that Cor Caroli consists of two stars in a wide orbit around one other. One of the stars is about half again as massive as the Sun, and several times brighter. The other is about three times the Sun’s mass, and more than a hundred times its brightness.

But over a period of about five and a half days, the heavier star’s brightness varies by about 15 percent. And that’s because of the starspots.

The star’s magnetic field is more than a thousand times stronger than the Sun’s. That produces giant spots – far bigger than anything ever seen on the Sun.

The spots are thousands of degrees cooler than the surrounding gas. The combination makes them darker than the rest of the surface. As the star rotates, the spots move in and out of view, causing the star to get fainter and brighter – a big “flutter” for the Heart of Charles.

Tomorrow: an astronomer with a “cloudy” name.

Script by Damond Benningfield