Roger's SkyPix

Visual Effects

Rainbows near Sunset

Rainbows near Sunset

A double rainbow graces the springtime sky shortly before sunset. The area between the two rainbows seems to have less light than the area inside the main bow, especially near ground. The darker area is called "Alexander's Dark Band," named after the Greek commentator Alexander of Aphrodisias, who wrote about the phenomenon around A.D. 200. Normally the rainbows have more blue and purple than this, and the area inside is more white. Since this is almost sunset, the atmosphere already has stripped much of the blue and violet from incoming sunlight before it reached the drops, making less of those colors available to the rainbows and giving a peachy tint to the bright patch within. The outer (secondary) rainbow is fainter and farther out because its light has been reflected twice inside the drops before passing out again at an even higher angle from the sun's opposite point. That double-pass through the raindrops also reverses the order of its colors compared to the primary rainbow.

2 SSW Pauls Valley OK (8 May 5) Looking E