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Simply a multicoloured arc made by light striking water droplets, the rainbow is an element of myths and superstitions in many different cultures. Rainbows have been portrayed as bridges between people and supernatural beings or as the bridges human ancestors used to descend to Earth. Because the shape of a rainbow resembles the bow of an archer, it is believed that it is used to shoot arrows of lightning. Generally seen as positive symbols of hope, in some cultures rainbows are viewed as negative omens. The most famous legend of the rainbow is the pot of gold at its end which is guarded by an elusive leprachaun. A rainbow is an optical phenomenon (some have called it an optical illusion) that does not exist in a specific spot in the sky. It appears when sunlight and atmospheric conditions are just right, and the viewer is in just the right position to see it. It is the result of the refraction and reflection of light. Light entering a water droplet is refracted or bent and is then reflected or bounced back by the inside of the water droplet. As this reflected light leaves the droplet, it is refracted again at multiple angles and separates into its component wavelengths or colours, creating a rainbow. In order for a rainbow to be seen, the sun or other source of light must be behind the viewer and the water droplets in front. The water droplets are usually raindrops, but could also be spray from a waterfall, a fountain, or even fog. Sunlight is made up of many different wavelengths of light, and each is reflected at a different angle, with some being bent more than others. Red is the longest wavelength of visible light and is refracted or bent the least, while violet is the shortest wavelength and bends the most. When the light exits the water droplet it is separated into all its wavelengths, and we see the band of separate colours, with red on the outer arch and violet on the inner arch of the rainbow. The other familiar colours of the rainbow as we see them in order of wavelength, are orange, yellow, green, blue and indigo. At their edges, the colours of the rainbow overlap. This produces a sheen of "white" light, making the inside of a rainbow much brighter than the outside. |
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There are various types of rainbows, depending on the light, water droplets and viewer angle. When rain is falling between the viewer and the sun, the light passes through the raindrops rather than being reflected by them, causing the atmosphere opposite the rainbow to appear to be glowing. Sometimes one may see a double rainbow, a faint secondary rainbow above the primary one, which is caused by light being reflected twice inside the raindrop. In this case, the colours are reversed, with red on the inner arc with violet on the outside. A twinned rainbow is two distinct rainbows produced from a single endpoint, which is the result of light being refracted in a raincloud with different sizes and shapes of raindrops. |
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A reflection rainbow appears when a primary rainbow is reflected above a body of water. Reflection rainbows do not mirror the primary rainbow, but often appear to stretch above it. At sunrise or sunset, it is sometimes possible to see a red rainbow. A fogbow is formed in much the same way as a rainbow, but because the water droplets are much smaller, the fogbow is much fainter than a rainbow, and some fogbows have few detectable colours at all, appearing mostly white, with a reddish tinge on the outer edge and a bluish tinge on the inner edge. A moonbow or lunar rainbow, as its name suggests, is a rainbow produced by light reflected by the moon. Because the moon itself does not emit light, moonlight is reflected sunlight, as well as some starlight and "Earthlight." |
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From an aeroplane in the right conditions, one is sometimes lucky enough to see a circular rainbow. A full rainbow is actually a complete circle. Viewers on the ground can only see the light reflected by raindrops above the horizon, making it impossible to see a full rainbow from the ground. The amount of the rainbow arc that is visible depends on how high the sun is in the sky. The higher the sun is, the less of the rainbow is visible above the horizon. Because each person’s horizon is slightly different, no two people see the same rainbow. So sadly, the pot of gold will never be found because none of us sees the same rainbow and being a circle, the rainbow has no end! |
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