The science
Kepler. Orbits are ellipses with the Sun at a focus; the radius vector sweeps equal areas in equal times, dA/dt = πab/P; and P² = a³ (years, AU).
M = L - w mean anomaly
M = E - e sin E Kepler's equation (Newton)
nu = 2 atan2(sqrt(1+e) sin E/2, sqrt(1-e) cos E/2)
r = a(1 - e cos E), lambda = nu + w
C(M) ~ 2e sin M + 1.25 e^2 sin 2M
train: theta_p/theta_E = (a/b)(c/d)
drift = 360[(a/b)(c/d)/P_E - 1/P_p] per yr
Assumptions. Typical mean J2000 elements (spot-check against the JPL approximate-positions table), constant elements, coplanar orbits, Earth's wheel is the 1:1 reference, orbit radii compressed for display.
Checks. running...