Rainbow

A rainbow is a coloured arc that occurs when sunlight shines onto falling raindrops and is refracted, then reflected back towards the observer. In this process, each drop acts as a tiny prism, splitting the sun's rays (according to wavelength) into their component colours. One of the reflected bundle of rays is much more intense than the rest and emerges at an angle of 42° to the direction of incoming sunlight. The strong reflections from each drop of similar size reinforce each other and a visible image of the sun's spectrum appears as an arc (ie, a primary rainbow). Occasionally, sunlight and rainfall may be intense enough to produce a second, fainter rainbow above or beyond the first. The secondary rainbow results from 2 internal reflections of light in raindrops and occurs at an angle of 50° (compared to the one internal reflection and 42° angle of primary rainbows). As rainbow formation requires that the sun be visible in some part of the sky while rain is falling in another, rainbows are seldom seen during extensive frontal-type rains but are restricted to thunderstorms and light showers. Because of the angle requirement, they are also more likely to be observed during or just after late afternoon showers. Rarely, the light of the full moon may be bright enough to produce a rainbow arc from a night shower.