Why, when the planet is accelerated during the ‘close phase’ of its orbit, isn’t it then flung away? I get that gravity pulls/holds it in orbit but why hasn’t it flattened out into a spherical orbit?
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I feel like the simplest explanation is that a circle is just a special form of ellipse, with a very specific requirement that the two foci of the ellipse be at the same point. For that to occur takes some extremely specific circumstances, even excluding the fact that space includes significantly more than just the planet and orbited body in question. External forces, even if small, force some eccentricity into the orbit. Orbiting bodies pull on each other and cause them to ‘wobble’ slightly. The sun pulls on the earth, as the earth pulls on the sun. But our moon is also pulling on the earth, while being pulled on itself. The effect is substantially smaller, but does exist, and causes that orbital foci to very slightly wobble as well.
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