I remember Stokes parameters as a way to completely define the polarization state of a well-defined beam of light. However several questions here refer to Stokes parameters used in characterizing the morphology of galaxies.
In Optics it's $S_0, S_1, S_2, S_3$ and in Astronomy it's $Q, U$.
I'm guessing that these are not exactly the same set of parameters. but there might (or might not) be some connection either historically or in the way some observations were made.
- How did they both end up being called Stokes parameters? Is there a relationship?
- How are they calculated (equation and/or short explanation please, not just a link)