def uk_to_mjy(t_uK, nu_GHz, th_arcmin):
    """Convert brightness temperature [uK] to flux density [mJy].

    See equation at https://science.nrao.edu/facilities/vla/proposing/TBconv:
        T = 1.36 * ( lambda[cm]^2 / theta[arcsec]^2 ) * S[mJy/beam]

    Parameters
    ----------
        t_uK: brightness temperature in uK
        nu_GHz: frequency in GHz
        th_arcmin: FWHM in arcmin

    Returns
    -------
        s_mJy (float): flux density in mJy
    """
    l_cm = 3e1 / nu_GHz # wavelength [cm]
    t_K = t_uK / 1e6
    th_arcsec = th_arcmin * 60.
    s_mJy = t_K / 1.36 / (l_cm/th_arcsec)**2

    return s_mJy