eli5 can someone explain what causes Northern Lights!
In: Physics
The Sun, like most stars, has powerful magnetic fields. They’re so powerful, in fact, that they fling charged particles around in the Sun’s atmosphere at considerable speeds.
Some of these particles get flung off into space. This happens a little bit all the time (the *solar wind*) and in big bursts sometimes (a *coronal mass ejection* = “the outside of the sun spits stuff out”, aka a CME). CMEs are more common at the peaks of the Sun’s 11-year sunspot cycle, which is currently close to its maximum (which is why the sun just fired off a really big one).
Those ejected particles fly outward into space. Most eventually fly all the way to the edges of the solar system, but some of them get caught in the magnetic fields of the planets (when they have them – not all planets do, but Earth does).
When they get caught in Earth’s magnetic field, the field deflects them off of their original course, and tends to funnel them towards the magnetic poles of the Earth. If you imagine the Earth’s magnetic field as a bar magnet, the magnetic poles would be the poles of that bar magnet. In reality it’s a bit more complicated than that, but the bar-magnet-like field (what we’d formally call a *dipole approximation*) is close enough for a decent understanding. These poles are close to aligned with the Earth’s geographic poles around which the Earth rotates – the north magnetic pole is currently near the northern coast of Canada, close to but not quite identical to the geographic North Pole.
Once the particles reach the poles, they follow the magnetic field lines “down” towards the Earth, and eventually strike the Earth’s atmosphere in a circle that is usually close to the magnetic poles. The particles are moving extremely fast, so when they strike, they tend to blast electrons off of the atoms in the atmosphere. That leaves a “slot” open in the atom that other electrons can occupy. When they do, they release energy in the form of light. The green, purple, and red colors of a typical aurora come from the different kinds of gas common at different altitudes in the atmosphere.
When lots of particles strike the Earth from a big CME, there’s more glow and it’s more spread out, leading to wider and brighter aurora displays like the ones you may have seen a few days ago.
TLDR: sun shoots particles at us, particles follow magnetic field to poles, particles knock atoms apart, that makes atoms glow.
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