When the charged particles of a star's upper atmosphere get powerful enough, it escapes its gravity and gets released into space. That's called a solar wind. And if that solar wind stays strong when it hits the Earth's magnetic field - or in this case, Arslae's magnetic field, it causes an aurora. You know how you drop a stone into water, and the surface ripples? It's like that, only it shows with an aurora.

[It's way more complicated than that, but Clay's all about simplifying something so that those who don't have a science degree can understand and appreciate it.]