;+
; NAME:
;	ToSolarRadii
; PURPOSE:
;	Returns factor needed to convert distance to solar radii
; CATEGORY:
;	Thomson scattering
; CALLING SEQUENCE:
	FUNCTION ToSolarRadii, au=au
; OPTIONAL INPUT PARAMETERS:
;	au=au		if not set then rpau=1 is returned
;			if set then the number of au per solar radii is returned
; OUTPUTS:
;	Result		multiplicative factor to convert to solar radii
; INCLUDE:
	@compile_opt.pro		; On error, return to caller
; CALLS:
;	InitVar
; PROCEDURE:
;	Many of the Thomson scattering procedures have a keyword /au to indicate
;	that in- and output distances are in AU rather than the default units of
;	solar radii. This function provides the conversion factor needed to
;	convert to solar radii irrespective of the setting of keyword /au.
; MODIFICATION HISTORY:
;	FEB-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu
;-

InitVar, au, /key

CASE au of
0: rpau = 1
1: rpau = 1/!sun.RAu		; Converts AU to solar radii
ENDCASE

RETURN, rpau  &  END