This presentation is devoted to describe the formation of the rainbow. The theory of the rainbow started in the man’s sense of wonder thousands of years ago. About 2,500 years ago, Aristotle suggested the first theories that explain the formation of the rainbow. Many scientists studied and suggested different theories to try to improve the understanding of the appearance of the rainbow. The theories of Aristotle, Descartes, Newton, Fermat, and Snell are specifically described in this presentation. By using several calculus equations, it can be proved that the different colors of the rainbow have different angles of observation. This presentation mainly focuses on the observation angles of red and violet light. The angles of observation for these two colors are also proved to be different in the second rainbow and the third rainbow. Even now in the beginning of the twenty-first century, the formation of the rainbow is not understood in all details.