What Is A Rainbow?
What Is A Rainbow?
We normally only see an arc of a rainbow, but all rainbows are actually full circles. Most people see an arc or, if lucky, a semicircle because they are standing on the ground and the rest of the rainbow is cut off by the horizon.
Rainbows are formed when sunlight is scattered from raindrops into the eyes of an observer. Most raindrops are spherical and it is this shape that provides the conditions for the rainbow to be seen. A raindrop is like a prism, refracting ‘white’ light form the Sun into its seven component colours or the colours of a rainbow: red, orange, yellow, green, blue, indigo, violet. (ROYGBIV)
Rainbows only appear semi-circular over level ground at sunrise or sunset, when the sun is exactly on the horizon, the majority of the time a smaller segment of an arc is seen
A double rainbow is a wonderful sight, but this phenomenon is relatively common, especially when the sun is low in the sky as in this photo
Interestingly the colours of the second rainbow above are less distinct and reversed VIBGYOR. The darker band between the two semicircles is called Alexander’s Band, named after Alexander of Aphrodisias, who first described it in 200 AD