Earth is in a stable orbit sure, and I don’t think the aphelion and perihelion are changing but the orbit is slowly rotating around the Sun ultimately drawing a kind of flower-like shape. Why? Why does that not end up changing our aphelion and perihelion?
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You’re talking about [apsidal precession](https://en.wikipedia.org/wiki/Apsidal_precession). It happens for a few reasons, but the dominant one is the effect of the gravity of the other planets. (Relativity also plays a role, because gravity is not quite the 1/r^(2) force it would be in Newtonian gravity; there’s an extra 1/r^(3) force unique to relativity that is very small but nonzero. But the relativistic effect, while historically important, is small relative to the effects of the other planets.)
Note that the effect on Earth is *very* small; it takes many millennia for the Earth’s orbit to precess around the Sun one time.
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