What is more exciting than a rainbow? A double rainbow.
But what is a rainbow and how can there be two at the same time? Well according to How Stuff Works, a rainbow is an optical and meteorological phenomenon that is caused by both refraction and reflection of light in water droplets which results in a beautiful spectrum of light appearing in the sky. This spectrum takes the form of a multicolored arc. Rainbows which are caused by sunlight always appear in the section of sky directly opposite the sun.
In a rainbow, the raindrops in the air act as tiny prisms. Sun light enters these raindrops, reflects off of the side of the drop and exits. In this process, it is broken into a spectrum just like it is in a triangular glass prism.
Even though rainbows can be full circles, the average observer sees only an arc, formed by those illuminated droplets above the ground.
Now in a double rainbow, a second arc is seen outside of the primary arc, and has the order of its colors reversed with red facing toward the other one, in both rainbows. Double rainbow is caused by a double reflection of sunlight inside the raindrops and appear at an angle of 50–53°. As a result of the second reflection, the colors of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow in a double rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky. The dark area of unlit sky lying between the primary and secondary rainbows is called Alexander’s band, after Alexander of Aphrodisias who first described it.
The rainbow comes up a lot of times in folklore and mythology. For instance, in a Chinese folktale, Hsienpo and Yingt’ai are star-crossed lovers who must wait until the rainbow appears to be alone together. Hsienpo is the red in the rainbow, and Yingt’ai is the blue. For Buddhists, the rainbow is “the highest state achievable before attaining Nirvana, where individual desire and consciousness are extinguished.”
The one most of us are most familiar with is in Ireland, a common legend asserts that a “pot of gold” is to be found at the end of a rainbow, for the person lucky enough to find it. This treasure is, however, guarded by a Leprechaun.
All I know for sure is in my eyes, whenever I see a double rainbow, it always makes me smile.