Isn’t the 3 body problem (sun, Earth, Moon) very difficult to solve? How did humans predict future eclipses decades even centuries ago?
In: Planetary Science
Has your dad ever held you by your arms and swung around in a circle? That’s basically how orbits work. Instead of having arms planets have gravity to hold them together.
When your dad swings you around like this he has to lean back quite a bit to not topple over. This is because your weight (~18kg for a 5 year old) is not *that* far away from your dad’s (lets say ~90kg).
Now imagine your dad swinging around a bar of soap. Do you think he’d still have to lean back to not topple over? No, right? That’s because the soap bar is so much lighter than your dad. The bar of soap and your dad are like Earth and the Moon. While Earth/Dad feels a bit of an effect from swinging the moon/soap around it is definitely the moon/soap that feels more.
What if your dad was the sun? What could we use to picture Earth? A grain of sand or a tiny down feather! Your dad is going to be completely unaffected by swinging around a grain of sand.
And so it is with Earth, the Sun and the Moon. The moon might be tugging on Earth ever so slightly but from the perspective of the sun, its almost like we’re not even there. And the same happens in calculations. Using two 2-body problems is basically good enough.
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