Template:Atmosphere portal/Featured article/May 2005

A rainbow is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the sun shines onto falling rain. It is a multicoloured arc with red on the outside and violet on the inside. The full sequence of colours is red, orange, yellow, green, cyan, blue and violet.

The rainbow effect can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude or angle. The most spectacular rainbow displays when half of the sky is still dark with draining clouds and the observer is at a spot with clear sky overhead. Another common place to see the rainbow effect is near waterfalls. Rainbow fringes can sometimes be seen at the edges of backlit clouds and as vertical bands in distant rain or virga. The effect can also be artificially created by dispersing water droplets into the air during a sunny day.

In a very few cases, a moonbow, or night-time rainbow, can be seen on strongly-moonlit nights. As human visual perception for colour in low light is poor, moonbows are perceived to be white.