Hello, I'm new here, but I have a question regarding Kirchoff's law (I think its Kirchoff's law, but I'm not sure). I'm looking at it now, and it says that E=M/Msub b. I know that the equation gives the emmittance of an object, but I don't know what emmissivity or emmittance is! Any help would be greatly appreciated. Also, what's a P-Cygni profile for supernovae? I'm doing some research into supernova light curves, and from what I've found, Type II-P supernova have P-Cygni profiles, but the only sites I've found either too complex or too simple for what I need. Again, any help would be appreciated!