Christmas Day Rainbow
April 03, 2009
This photo of a lovely double rainbow was taken by my granddaughter Gaby using her cell phone camera in Moreno Valley, California. It was captured around 3:00 p.m. (local time) on Christmas Day 2008. Notice that the colors in the secondary rainbow (the fainter bow at top) are reversed from those of the brighter primary bow indicating a secondary reflection. Colors are somewhat smeared in rainbows because, unlike a prism in which the refracted rays of sunlight remain parallel, the rays that emerges from raindrops diverge. The darkened region in between the bows is known as Alexander's Band, after Alexander of Aphrodisias who first chronicled it around 200 A.D. Rays of sunlight passing through raindrops between the angles of about 42 and 51 degrees (corresponding to the angle of the primary rainbow and the secondary bow, respectively) fail to reach our eyes; hence the sky in this region appears relatively dark.