function dr_carr,lat,arg,ang2tim=ang2tim,rad=rad,period=period if n_elements(lat) eq 0 then lat = 0. if n_elements(ang2tim) eq 0 then ang2tim = 0. if n_elements(rad) eq 0 then rad = 0. if n_elements(period) eq 0 then period = 0. latrad = lat/!radeg sid_sun = 2.865 - 0.351*(sin(latrad))^2 - 0.443*(sin(latrad))^4 sid_earth = (2*!pi*1e6)/(365.25*86400.) omega = sid_sun - sid_earth if n_elements(arg) eq 0 then begin ; Rotation rate at latitude LAT ; was requested if period ne 0 then return, 2e6*!pi/omega/86400 else $ if rad eq 0 then return, omega/1e6*180/!pi*86000 else $ return, omega endif if ang2tim eq 0 then begin out = omega*arg*.0864 ; Rotation angle in radians if rad eq 0 then out = out*!radeg ; Convert to degrees if requested endif else begin out = arg/omega/.0864 ; Required rotation time in days if rad eq 0 then out = out/!radeg ; Input was in actually in degrees endelse return, out end