;+
; NAME:
;	ThomsonSolarFlux
; PURPOSE:
;	Calculates the flux from the solar disk incident on
;	an observer at given distance from Sun
; CATEGORY:
;	Thomson scattering
; CALLING SEQUENCE:
	FUNCTION ThomsonSolarFlux, R, U
; INPUTS:
;	R		array; type: float; default: 1 AU
;				distance from Sun (in solar radii)
;	U		array; type: float; default: zero
;				limb darkening constant
; OUTPUTS:
;	Flux	array; type: float
;				flux from the solar disk in units of pi*I0
; INCLUDE:
	@compile_opt.pro		; On error, return to caller
; CALLS:
;	InitVar
; PROCEDURE:
;	The flux from the solar disk expressed in the intensity at
;	the center of the disk, I0, is pi*I0*(1-u/3)*(Rsun/R)^2.
; MODIFICATION HISTORY:
;	AUG-1999, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
;-

InitVar, U, 0.0
InitVar, R, 1/!sun.RAu	; 1 AU in units of solar radii

RETURN, (1.-U/3.0)/(R*R)  &  END