Here's how it works:

1. Solar Flares and CMEs: The sun's surface is constantly in motion, with powerful magnetic fields that can become tangled and unstable. This instability can cause solar flares, which are sudden bursts of energy and radiation. Sometimes, a flare can trigger a coronal mass ejection (CME), which is a giant cloud of superheated plasma and magnetic field lines that are blasted out into space.

2. Earth's Magnetic Field: As a CME travels through space, some of its energy and particles can reach Earth. Our planet has a magnetic field that protects us from most of this radiation, but the CME's energy can interact with the magnetic field at the poles.

3. Auroral Display: This interaction between the CME's energy and Earth's magnetic field causes particles to become energized and flow along the magnetic field lines towards the poles. When these energized particles collide with atoms in the Earth's atmosphere, they release energy in the form of light, creating the stunning visual display we call the aurora borealis (northern lights) and aurora australis (southern lights).

So, in short, CMEs are the primary cause of auroras.