The residuals for the longitude fit in the last blog have arc second accuracy. Here are the final correction for the longitude fit and resulting residuals.
The periodic sin function present appears to be associated with the Moon orbital motion and can be removed leaving a long term residual.
This may be due to planetary perturbations and/or errors in the fit. The lunar synodic period works quite well with time measured in days. The fit of Sun's motion with the lunar disturbance of the Earth's position added appears to have about 10 arc second accuracy.