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?
In: 2204
Think of a giant frozen lake. There’s a post in the middle with a rope tied to it.
You’re on the edge of the lake, on ice skates, holding the rope.
Try to haul yourself to the post, it’s easy: just pull on the rope.
But now imagine you’re skating hell-for-leather at right-angles to the direction of the rope.
Try to haul yourself in now, and it won’t work, all you’ll do is swing around. No matter how hard you haul on the thing, you just can’t reach the post – *your turning circle is too big to let you*.
You physically cannot by any means reach the centre of the lake without slowing down. Especially as you’re not really on ice-skates, but big blocks of wet ice that give you no traction whatsoever.
That’s orbit. That’s all it is: a big turning circle, and no way to dump your speed. You can’t just suddenly pull a 90-degree turn, so you can’t ever hit the thing you’re orbiting.
Now for geostationary orbit:
Imagine that on top of the post, there’s a carousel. One of those stately fairground ones with the horsies, which takes like an hour to go round.
Is it possible to swing around the post, but stay lined up with one particular horse?
Sure it is – if you’ve got a really huge lake and a really long rope.
If you’re skating far enough out that it takes you an hour to do a full circuit – exactly the same time as it takes one of the horsies to go round – then you’ll stay lined up. From the horsie’s perspective, you’re not moving at all.
And that’s geostationary. You have a big enough orbit, it takes 24 hours to go round the earth, the same as the continents on the surface. From their perspective, you’re not moving at all, just hovering in the air (even though you’re hurtling through space at terrifying speeds).
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