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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 droplets of moisture in the Earth's atmosphere. A rainbow does not actually exist at a location in the sky, but rather is an optical illusion whose apparent position depends on the observer's location. Even though a rainbow spans a continuous spectrum of colours, traditionally the full sequence of colours is most commonly cited as red, orange, yellow, green, blue, indigo, and violet. Indigo is usually included despite the poor ability of humans to distinguish colours in the blue portion of the visible spectrum because the wavelength of green is roughly in the middle of the visible light spectrum. Photo credit: Wing-Chi Poon |
