[Steuard]

Maybe it's worth mentioning that we're all at least a little bit familiar with dispersion in other contexts: it's the same phenomenon that makes a prism work to split white light into colors, and that is responsible for rainbows. (The angle that light bends when passing through a surface depends on the precise speed that light of that frequency travels on each side. When different frequencies have different speeds, that's dispersion, and what started as combined white light splits into a different color at each angle.)