Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be feet in the air with the precise amount of ice crystals, and the sun must hit the clouds at 58 degrees. (a/k/a Sun Doggies)
The sea is a big part of the book. The sea is where mostly everything takes place and the old man spends most of his time. Fishing is the old mans passion and being on the sea is something that he is used to and enjoys.