Subroutine:   IRCO_SUNREF
 
 Purpose:      construct a sunreferenced coordinate system
 
 Category	WORLD COORDINATES, IRAS

 File:         irco.shl
 
 Author:       Do Kester
 
 Person resp.: Do Kester
 
 Address:      guspace!do or rugfx4!do         (uucp)
 
 Use: call irco_sunref(
 	sunlong )	I  	doubleprecision
 
 	sunlong	longitude of the sun

 Description:  
 	A sunreferenced coordinate system will be created with
 	respect to the present ecliptic coordinate system.
	SUNLONG is the angular distance of the sun to the 
	first-point-of-aries i.e. the ecliptic longitude of
	the sun.
 	All transformation matrices pertaining to the 
 	sunreferenced system will be overwritten with 
	matrices referring to this solar longitude.
	
 Externals:    
 
 Updates:      25 Apr 1990 DK, documentation only
		10 Oct 1990 DK, fill in connect with the proper systems
		26 Nov 1990 DK, sunlong is stored as epoch in radians