Explanations
The bouncing back of light when it strikes a surface, like the inner surface of a raindrop.
The splitting of white light into its constituent colors (spectrum).
Act as tiny prisms, bending and reflecting sunlight to form the arc.
Features a single reflection inside raindrops, with red on the outside and violet on the inside.
The bending of light as it passes from one medium (air) to another (water).
Must be behind the observer, with the sun's rays striking the raindrops in front.
Involves two internal reflections, resulting in colors reversed (violet on outside, red on inside) and being fainter.