The rayleigh is a unit of
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are Massless particle, massless ...
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...
, used to measure faint light emitted in the sky, such as
airglow
Airglow (also called nightglow) is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffu ...
and
aurora
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...
s. It was first proposed in 1956 by
Donald M. Hunten
Donald is a masculine given name derived from the Gaelic name ''Dòmhnall''.. This comes from the Proto-Celtic *''Dumno-ualos'' ("world-ruler" or "world-wielder"). The final -''d'' in ''Donald'' is partly derived from a misinterpretation of the ...
,
Franklin E. Roach
Franklin Evans Roach (September 23, 1905Obituary, Osterbrock, ''BAAS'', p. 1608. – September 21, 1993Obituary, Osterbrock, ''BAAS'', p. 1610.) was an American astronomer, astrophysicist, geophysicist, professor, and scientist analyzing UFO ...
, and
Joseph W. Chamberlain
Joseph is a common male given name, derived from the Hebrew Yosef (יוֹסֵף). "Joseph" is used, along with "Josef", mostly in English, French and partially German languages. This spelling is also found as a variant in the languages of the m ...
. It is named for
Robert Strutt, 4th Baron Rayleigh
Robert John Strutt, 4th Baron Rayleigh (28 August 1875 – 13 December 1947) was a British peer and physicist. He discovered "active nitrogen" and was the first to distinguish the glow of the night sky.
Early life and education
Strutt was bor ...
(1875–1947).
Its symbol is R (also used for the
röntgen, an unrelated unit).
SI prefix
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...
es are used with the rayleigh.
One rayleigh (1 R) is defined as a column emission rate of 10
10 photons per
square metre per column per
second. Note that rayleigh is an apparent emission rate, as no allowances have been made for scattering or absorption. The night sky has an intensity of about 250 R, while auroras can reach values of 1000 kR.
The relationship between photon
radiance
In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Radiance is used to characterize diffuse emission and reflection of electromagnetic radiatio ...
, ''L'', (in units of photons per square metre per second per
steradian
The steradian (symbol: sr) or square radian is the unit of solid angle in the International System of Units (SI). It is used in three-dimensional geometry, and is analogous to the radian, which quantifies planar angles. Whereas an angle in radi ...
) and ''I'' (in units of rayleighs) is
:
References
{{reflist
Units of luminous flux