(power reaching a surface from a specific source)
Intensity in astronomy (commonly called radiance outside astronomy)
is a measure of electromagnetic radiation striking
a surface from a given solid angle, i.e., source.
Alternately, electromagnetic radiation from a surface
radiating within a solid angle can use the same measure.
A common unit is watt per steradian per square meter.
L = ————————
- L - intensity
- Φ - power in watts
- Ω - solid angle in steradians
- θ - angle between source and normal of the source
This is the common use of the term intensity in astronomy,
but in physics, the term is often used all electromagnetic
radiation striking a surface in watts per square meter.
Thus the Physics term radiance to distinguish meanings.
Specific intensity or spectral radiance is the intensity
at a specific wavelength.
The mean intensity is the average intensity in all directions
from a surface (perhaps within a solid angle), i.e., integrating it
over the angle and dividing by 4π. It can also be specific,
i.e., per wavelength. The mean intensity can be useful in
Referenced by pages:
Balmer jump (BJ)
brightness temperature (TB)
color-magnitude diagram (CMD)
globular cluster (GC)
imaging Fourier transform spectroscopy (IFTS)
Kramers opacity law
line shape function
optical depth (τ)
Rosseland mean opacity
equation of radiative transfer (RTE)
source function (S)
stellar temperature determination
surface brightness profile
Sunyaev-Zel'dovich effect (SZ effect)
Very Small Array (VSA)
Wien's displacement law