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+include	<math.h>
+
+# The sun's velocity with respect to the local standard of rest is:
+
+define	RAVSUN	18.	# RA of sun's velocity
+define	DECVSUN	30.	# DEC of sun's velocity
+define	VSUN	20.	# VLSR of sun
+define	EPOCH	1900.	# Epoch of sun's velocity
+
+# AST_VSUN -- Projection of the sun's velocity along the given direction.
+
+procedure ast_vsun (ra, dec, epoch, v) 
+
+double	ra		# Reference right ascension (hours)
+double	dec		# Reference declination (degrees)
+double	epoch		# Epoch (years)
+double	v		# VLSR of sun along reference direction
+
+double	ravsun, decvsun, vx, vy, vz, cc, cs, s
+
+begin
+	# Precess VLSR direction to current date.
+	call ast_precess (double (RAVSUN), double (DECVSUN), double (EPOCH),
+	    ravsun, decvsun, epoch)
+
+	# Cartisian velocity components of the sun's velocity.
+	vx = VSUN * cos (DEGTORAD (15. * ravsun)) * cos (DEGTORAD (decvsun))
+	vy = VSUN * sin (DEGTORAD (15. * ravsun)) * cos (DEGTORAD (decvsun))
+	vz = VSUN * sin (DEGTORAD (decvsun))
+
+	# Direction cosines along the reference direction.
+	cc = cos (DEGTORAD (dec)) * cos (DEGTORAD (15. * ra))
+	cs = cos (DEGTORAD (dec)) * sin (DEGTORAD (15. * ra))
+	s  = sin (DEGTORAD (dec))
+
+	# Project sun's motion along the reference direction.
+	v = -(vx * cc + vy * cs + vz * s)
+end