The secondary rainbow, also called a double rainbow, but is in fact the outer of the two rainbows in a double rainbow, and has always proven to be quite hard to view, but not impossible.

The secondary rainbow is nearly always fainter than the primary, usually about 43% of the total brightness of the primary. The secondary′s colors are reversed with the red being on the innermost edge of the secondary rainbow. Too, the colors are more widely separated making the secondary rainbow broader than the primary.

The secondary has a radius of 51° and both the primary and secondary are concentric sharing the same antisolar point for a center.

When light rays enters a raindrop, it is reflected on the inside of the drop and can be reflected one or more times before escaping the drop. If the light rays escapes the drop after one reflection, they forms a primary rainbow. If the light rays escapes the raindrop after two internal reflections, they forms a secondary rainbow.

Light rays escaping a raindrop after more than two internal reflections do something entirely different. Instead of creating a another (or third) rainbow above the secondary rainbow, the light rays are directed back towards the sun which then can forms Third and Forth order rainbows around the sun.

At sunrise and sunset, always look to the direction opposite the sun for a possible rainbow. However, rainbow may appear at any time, so be alert to the three events that make rainbows more likely: (a) bright sunlight; (b) rain in the sky opposite from the sun: and (c) the time being near to the suntouch.