The Goldfish Over the Rainbow

摘要

A goldfish isn’t always visible inside its fishbowl. If the fish gets sufficiently close to the bowl glass, it will disappear for certain angles of observation. In a recent paper in this journal,1 Zhu and Shi explained the effect in terms of total internal reflection. We show in what follows that the phenomenon involves some richer optics: a rainbow defines one of the boundaries of the “blind zone” where the fish disappears.