A unit of luminous flux used to measure air glow, for example of aurora, first proposed in 1956.¹ Symbol, R. The SI prefixes are used with this unit. One rayleigh is 1010/4pi quanta per square meter per second per steradian.

The night sky has a luminous intensity of about 250 rayleigh, while auroras can reach values of 1000 kilorayleigh.

The unit is named for Robert John Strutt, fourth Lord Rayleigh (1875 – 1947).

D. M. Hunter, F.E. Roach, and J.W. Chamberlaine.
Journal of Atmospheric and Terrestrial Physics (GB) volume 8, page 345 (1956).

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