= Mutual inclination of nearly edge-on orbits
{title2=$I_m^2\simeq(\Delta I)^2+(\Delta\Omega)^2$}
For two nearly <edge-on orbits> with small <orbital inclination> difference $\Delta I$ and small <longitude of ascending node> difference $\Delta\Omega$, expanding the <dot product> of their normals gives $I_m^2=(\Delta I)^2+(\Delta\Omega)^2+O(\delta^4)$, with angles in radians and all offsets from edge-on of order $\delta$. Thus equality of observed sky-plane inclinations alone does not imply aligned <orbital planes>.
Back to article page
