Rayleigh (unit)

Rayleigh (Rl or R) is an off-system unit for measuring surface brightness . It is used in the study of auroras and the glow of the night sky . Introduced in 1956 by D. M. Hunter , F. E. Rauch, and D. W. Chamberlain ^[1] . Named after Robert Stratt , 4th Baron Rayleigh ( 1875 - 1947 ) ^[2] .

The radiation intensity of 1 RL corresponds to the emission of 10 ⁶ photons per second in a column with a cross-section of 1 cm ² (or 10 ¹⁰ photons in one second in a column with a cross-section of 1 m ² ):

1 RL = 10 ⁶ photons / (cm ² · s) = 10 ¹⁰ photons / (m ² · s).

The intensity in Rayleigh is numerically equal to the surface brightness of a uniformly luminous atmosphere increased by 4 π · 10 ⁻⁶ times (in units of photons per square centimeter of the area normal to the line of sight from the solid angle to one steradian , cm ⁻² · sr ⁻¹ ).

The unit can be used with multiple decimal SI prefixes , for example, CRL, MRL.

The surface brightness of the night sky in the absence of ground exposure is about 250 Rl. During auroras, the surface brightness of the sky can increase up to 1000 kilorelle (kRL).