def Calc_Ref_ET(Surface_temp, sl_es_24, Rn_ref, air_dens, esat_24, eact_24,
    rah_grass, Psychro_c):
    """
    Function to calculate the reference evapotransporation
    """
    Lhv = (2.501 - 0.002361 * (Surface_temp - 273.15)) * 1000000.0
    LET_ref_24 = (sl_es_24 * Rn_ref + air_dens * 1004 * (esat_24 - eact_24) /
        rah_grass) / (sl_es_24 + Psychro_c * (1 + 70.0 / rah_grass))
    ETref_24 = LET_ref_24 / (Lhv * 1000) * 86400000
    return ETref_24, Lhv
