Whats the physics behind an aurora?

Question

I'm looking for explanations from people, links or copy and paste. Also I am interested in the aurora borealis mainly.

Answer 1

The Aurora Borealis and Aurora Australis (Northern Lights and Southern Lights) are caused by charged particles ejected from the Sun (known as the "solar wind") getting caught in Earth's magnetic field. The magnetic field is strongest near the poles, so that's where the effect tends to be observed.

When a charged particle encounters a magnetic field, it feels a force exerted sideways to its motion. This causes the particle to start traveling in a circle or spiral path. Any object traveling in a circle is experiencing centripetal acceleration. When a charged particle is accelerated (even if its speed doesn't change), it emits photons by a process called Bremsstrahlung ("braking radiation"). These photons are often in the visible range, which we can see.

So, you're seeing photons emitted from charged particles that are spiraling around in the Earth's magnetic field.

Answer 2

Ever heard of a neon, or a florescent light? Same principle.

Charged particles from the sun strike atoms in the Earth's atmosphere, giving them energy, and making an electron jump up one level. Later when the excited electron drops back down into its original orbital, it gives off the excess energy as a photon of visible light.

Answer 3

reflection and refraction of light through the ice crystals in the air when the air warms.