- Did I miss something in school? Plenty of things heavier than helium aren’t metal. Boron, carbon, nitrogen, oxygen, fluorine, neon… - In astronomy, nearly everything is hydrogen or helium. Like, over 98% of all matter is H or He. So it’s very useful to be able to talk about H, He, and “everything else”. They call that everything else “metals”. - Some stellar atmosphere models also add “alpha”, which provides an extra knob for the abundance of alpha-capture elements. If you need anything more than that, you’re doing some niche astrophysics. - Alpha being the elements up to iron? - Elements formed by alpha capture. Since alpha particles have 2 protons, it’s generally elements with an even number of protons. 
 
 
 
- Not for astrophysicists. They call basically everything a “metal”. Of course they know it’s wrong. But they keep doing it to annoy the chemists, I think. - We also label things as prime to trick mathematicians into thinking a derivative has occurred 
 
 
- Can speak only for myself, but yes absolutely correct. 
- Anything metal between two pieces of different metal is a sandwich 




