How many colours do you see in a rainbow? A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky.
People are taught that a rainbow shows seven colours – red on the top, followed by orange, yellow, green, blue, indigo and violet on the inner side.
However, seeing seven colours may not be true.
In the exhibition Kaleidoscope, a family friendly show about how light is refracted and reflected,
Pat Hanly’s image Rainbow over Mt Eden clearly shows six colours.
Around 1665, Isaac Newton performed experiments with a prism in which he identified seven colours. Prior to that, Robert Boyle described the spectrum he produced with a prism as “denoting the five consecutions of colours: Red, Yellow, Green, Blew, and Purple.” It is thought that Isaac Newton only saw five colours in the rainbow but added two more -orange and indigo – because the number seven had mystical significance denoting perfection and completeness.
Seven is a special number. We have seven days of the week, seven natural notes in most Western music and, during Newton’s time, only seven planets had been discovered. So, it made sense that there must also be seven colours in a rainbow.
Kaleidoscope is showing at Aratoi until mid-July.
