Mr Ball next treats us to a brisk description of the human eye (remember rods and cones from school biology?), an explanation of why Newton was right and Goethe wrong about the composite character of white light, and an account of the 19th-century regimentation of the continuous colour spectrum by means of colour wheels and other classifying devices.

ECONOMIST: Science and history of colour

That lengthens the wavelength of the light and shifts it towards the red end of the colour spectrum.

ECONOMIST: Fundamental physics

So we get to see the full beauty of the colour spectrum.

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The result is a spectrum of skin colour rather than a dichotomy.

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In the quasar spectra, some of the dark lines were shifted slightly towards the red end of the colour spectrum and others towards the blue end.

ECONOMIST: Fundamental physics

More distant objects are moving away from us - and each other - faster than nearer objects, which causes a shift of their apparent colour toward the red end of the spectrum - a "redshift".

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