I'd never heard of the 'green flash' or 'green rim' before this thread, but the lowest picture in Micca's link seems to confirm something I have long suspected - the apparent size of the rising or setting sun or full moon when it is just above the horizon isn't just an illusion caused by it's proximity to the trees and rooftops, as many 'experts' claim, but is caused by magnification when it is seen through the atmosphere near the horizon.