def viscosity(T, mu_0=1.83245E-5, T_0=296.15, S=110.4):
    
    """ calculates viscosity of the air
    
    Parameters
    ----------
    T : float
        measurement temperature
    mu_0 : float
        reference viscosity
    T_0 : float
        reference temperature
    S : float
        Sutherland constant of air
    
    Returns
    -------
    viscosity : float
        viscosity at T
    
    """
    
    return (mu_0 * ((T_0 + S) / (T + S)) * ((T / T_0)**1.5))