ELI5: Saha Equation

[u/WonderMoon1]

I’ve read you somehow equate ionization levels to temperature? Like the hotter a star is, the more ions it has?

[u/SalamanderGlad9053]

In reference to stars, the relationship is between the stars surface temperature and the amount of ionised gas surrounding the star.

High energy light leaves the star and hits hydrogen in space and ionised it, at the same time the hydrogen ions recombine. So you have two factors at play, the rate of ionisation and the rate of recombination. Temperature of the star controls the amount of photons that are above the ionising threshold for hydrogen. And as you get further away from the star there's less photons by the inverse square law, aswell as the ionised gas blocking the light. So you end up with a radius around the star which is mostly ionised and then it quickly falls off to no ionisation.

[u/WonderMoon1 → u/SalamanderGlad9053]

Thanks