Figure 2.
Oscillation of the angle θ in two models: with the entire Earth potential and with J2 term only. After about 2.5 yr (which corresponds near the middle of this figure, in which the total time-span is about 1.5 months) the oscillations are still almost the same within plotting precision. Here |$i=30^{\circ }$|, δa0 = 1 km.