Ch2. Specific Intensity in Astrophysics, introduction and definition

This lecture introduces specific intensity, the quantity we astronomers most often start with for descriptions of light and its transport through media. A simple thought experiment due to Castor is used to introduce it, which I think may offer a somewhat more intuitive definition than what I see in many texts. We also use this definition to introduce and define solid angle, the “2D angle” used all over in our later applications. We finalize by looking forward to the next lecture, where we’ll define and discuss in detail energy density of radiation field, the radiative flux vector, and the radiation pressure tensor.

0:00 Introduction
6:57 Definition specific intensity
11:05 Solid angle, introduction and definition
16:40 Units of specific intensity and introduction of cgs unit system
20:44 Summary and prelude to next lecture (on radiation energy density, flux, and pressure)

Part of course: Radiation Processes in Astronomy
Lecturer: Prof. Dr. Jon Sundqvist
Programmes where I teach it: KU Leuven Bachelor Physics & Master Astronomy & Astrophysics, Hasselt University Bachelor Physics (as video course)

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   • SUPERSTARS-3D  

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For original course black-board class lectures, see also here:
   • Radiation Processes in Astronomy