Rainbows

The other day at my first Austin Astronomical Society meeting since moving to Texas last month, I witnessed (along with the others in the group) a double rainbow. Rainbows themselves are always a treat to see along with sundogs, halos and the like. Make it a double and it becomes an exceptionally beautiful sight to see.

Rainbows are formed by sunlight diffraction within large droplets of water. The larger the droplet, the smaller the diffraction effect that produces a rainbow instead of similar cloud phenomena such as fog bows or glories. The main colors we typically see, starting from the outer to inner bands of the rainbow, are red, orange, yellow, green,blue, indigo and violet with a minute hue of colors in between.

Secondary rainbows are the result of sun rays escaping raindrops after the light has been reflected more than twice inside them. The color order of the secondary rainbow is always reversed from the primary as if mirrored and is more diffuse and widened. Rainbows are always opposite the Sun in the sky. The lower the Sun on the horizon, the taller the rainbow will be.

Les Cowely has a wonderful site for learning more about atmospheric phenomena. Here are a few links within that site to further explain rainbows.

Primary Rainbows, by Atmospheric Optics

Secondary Rainbows, by Atmospheric Optics

Please click PCW Archive for Atmospheric Phenomena for more observations.