/// <summary>
        /// Gets Besselian elements values for specified Juluan Day.
        /// </summary>
        /// <param name="jd">Julian Day of interest</param>
        /// <returns></returns>
        internal InstantBesselianElements GetInstantBesselianElements(double jd)
        {
            //if (jd < From || jd > To)
            //    throw new ArgumentException($"Polynomial Besselian elements valid only for Julian Day in range [{From} ... {To}].", nameof(jd));

            // difference, with t0, in step units
            double t = (jd - JulianDay0) / Step;

            return(new InstantBesselianElements()
            {
                X = X.Select((x, n) => x * Pow(t, n)).Sum(),
                Y = Y.Select((y, n) => y * Pow(t, n)).Sum(),
                L1 = L1.Select((l1, n) => l1 * Pow(t, n)).Sum(),
                L2 = L2.Select((l2, n) => l2 * Pow(t, n)).Sum(),
                D = D.Select((d, n) => d * Pow(t, n)).Sum(),
                Mu = To360(Mu.Select((mu, n) => mu * Pow(t, n)).Sum()),
                F1 = F1.Select((f1, n) => f1 * Pow(t, n)).Sum(),
                F2 = F2.Select((f2, n) => f2 * Pow(t, n)).Sum(),
                dX = Derivative(X, t),
                dY = Derivative(Y, t),
                dL1 = Derivative(L1, t),
                dL2 = Derivative(L2, t),
                dD = Derivative(D, t),
                dMu = Derivative(Mu, t)
            });
        }