Matthew Trimble

Radiative Processes in Astrophysics (Rybicki and Lightman) Reading Assignment Summary Chp. 1

Sec. 1.1

EM radiation is a spectrum of varying categories. c = wavelength*frequency. Energy = h*frequency. Temperature = Energy/k.

Sec. 1.2

When dealing with a macroscopic system, light can be viewed as rays, instead of individual photons. A source of light is isotropic if it emits an equal amount of energy in every direction, like a star. Flux is defined as energy per area per time.

Sec. 1.3

The specific intensity is the energy per area per time per solid angle per frequency. The net flux is the integral of the specific intensity*cos(angle away from the direction being measured along) d(solid angle). The momentum flux is 1/c * integral of specific intensity*cos^2(angle) d(solid angle). Net flux and momenrum flux are moments of the intensity. Flux = integral of net flux d(frequency). Momentum = integral of momentum flux d(frequency). Intensity = integral of specific intensity d(frequency). Specific energy density is the energy per volume per frequency range. dE = energy density as a function of solid angle*d(volume)*d(solid angle)*d(frequency). Specific energy density = (4*pi/c)*mean intensity. Mean intensity = 1/(4*Pi)* integral of specific intensity d(solid angle). Total radiation density = integral specific energy density d(frequency) = (4*Pi/c)* integral of the mean intensity d(frequency). The radiation pressure is 1/3 the energy density in an isotropic radiation field. The specific intensity of a ray is constant, meaning d(specific intensity)/d(length along ray) = 0. The flux at a uniformly bright surface = Pi*Brightness.

Sec. 1.4