def ballesteros_formula(color_bv):
    """
    Ballesteros formula.
    Estimate start temperature from B-V index.

    color_bv: B - V = -2.5 * log(F_b / F_v)

    :param color_bv: float; B-V index
    :return: float; temperature stimation
    """
    return 4600.0 * (1.0 / (0.92 * color_bv + 1.7) + 1.0 / (0.92 * color_bv +
        0.62))
