function difrot, Dt, Phi, hours=hours, seconds=seconds, $
days=days, degree=degree, radians=radians, latitude=latitude

;	Calculates new longitude(s) of point(s) on the Sun according to
;	the differential rotation. If the LATITUDE keyword parameter
;	is present, then the rotation is performed for the solid body.

if keyword_set(radians) then Kdeg=1. else Kdeg=!Dtor

	CASE 1 OF

keyword_set(seconds): Ktime=1/24./3600.
keyword_set(days): Ktime=1.

ELSE: Ktime=1/24.

	ENDCASE


if n_elements(latitude) le 0 then Lat=Phi else Lat=(Phi*0.+1)*latitude

	return,-(13.39-2.7*(sin(Kdeg*Lat))^2)*float(Dt)*Ktime*!Dtor/Kdeg

end