= Solution
Expanding the <disturbing function> in <orbital elements> gives a Fourier series of the form
$$
\mathcal R_1=
\sum_{\mathbf j}C_{\mathbf j}(a_1,a_2),
e_1^{m_1}e_2^{m_2}
\sin^{n_1}\!\frac{I_1}{2}
\sin^{n_2}\!\frac{I_2}{2}
\cos\Phi_{\mathbf j},
$$
where
$$
\Phi_{\mathbf j}=j_1\lambda_1+j_2\lambda_2
+j_3\varpi_1+j_4\varpi_2+j_5\Omega_1+j_6\Omega_2.
$$
The radial coefficients are combinations of <Laplace coefficients>. Rotational and reflection symmetry impose the <D'Alembert characteristic>: the integer coefficients sum to zero, nodal coefficients obey a parity rule, and each harmonic begins at the corresponding order in eccentricities and inclinations.
Back to article page
