eli5: I’ve heard orbit described as continuously falling past or missing the Earth, how then do objects in geosynchronous orbit above a single point not fall out of the sky?
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Imagine a tug-of-war rope between you and a friend, and you’re both facing each other. And you stay in one place in the middle because you’re much bigger than your friend. And your friend is running around you in circles as fast as he can, but you’re both holding on.
Geo-synchronous orbit is kind of like that, except your friend doesn’t have to keep expending energy running the whole time, since in space there’s no “ground” (or gravity) acting along the plane of the orbit for him to have to fight friction against.
The Earth and the satellites are “holding on” to each other, just the right amount of gravity to balance it perfectly, meanwhile they are spinning “around” each other, while facing each other. But really, the Earth is so big and the satellite is so tiny, that we barely notice the effect of the satellite on Earth’s movement — Whereas the effect of the Earth on the satellite’s movement is so strong, it keeps the satellite locked in the sky in the same position relative to the ground “beneath” it, and the Earth drags the satellite along as the Earth moves in a circle around the sun.
This is why Geosynchronous orbit is **only possible** at a **specific height/altitude.** For Earth, that altitude is 37,000 km. Below or above that, the “speed” required to maintain orbit is not equal to the speed at which the Earth spins, so it’s not possible to have a stable orbit which maintains its position relative to a spot on the ground beneath. (For heavier planets, the single geosync altitude would be higher and farther away… For lighter planets, it would be lower and closer to the planet.)
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