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
The closer you are to the surface of the Earth, the faster you have to be moving sideways in order to “miss” the Earth as you fall.
As you get farther from the surface, the speed necessary to continuously “miss” the Earth drops.
The Earth is also rotating. Close to the surface, you have to be moving much faster than the surface of the Earth to stay in orbit. Very far away, you can move slower than the Earth turns and still stay in orbit.
Between those two points, there is a specific height where the speed necessary to stay in orbit results in you taking 24 hours to orbit the Earth. This is the same time it takes for the Earth to turn once on its axis, so assuming that the orbit is happening approximately above the equator, it will appear that the satellite is hovering above you to someone standing on the Earth.
But it’s not hovering. It’s still “falling past” the Earth. It’s just falling past at the same rate and in the same direction that the Earth turns.
The closer you are to the surface of the Earth, the faster you have to be moving sideways in order to “miss” the Earth as you fall.
As you get farther from the surface, the speed necessary to continuously “miss” the Earth drops.
The Earth is also rotating. Close to the surface, you have to be moving much faster than the surface of the Earth to stay in orbit. Very far away, you can move slower than the Earth turns and still stay in orbit.
Between those two points, there is a specific height where the speed necessary to stay in orbit results in you taking 24 hours to orbit the Earth. This is the same time it takes for the Earth to turn once on its axis, so assuming that the orbit is happening approximately above the equator, it will appear that the satellite is hovering above you to someone standing on the Earth.
But it’s not hovering. It’s still “falling past” the Earth. It’s just falling past at the same rate and in the same direction that the Earth turns.
[Relevant xkcd](https://what-if.xkcd.com/58/)
The short version is that the earth is spinning too. There’s a distance from the earth where you can be going fast enough sideways to “miss” the earth when falling, i.e., be in orbit, but be moving at the same speed the earth is turning at. It’s pretty far out actually.
We call that distance “Geosynchronous Orbit”, since things in that position, moving sideways like that end up appearing to stay directly above the same point on the planet.
There is, of course, a much longer version, and it has to do with the satellite’s orbital velocity synchronizing with the gravitational force of the earth such that there’s an apparent relationship between a spot on the ground and the satellite, but it involves a lot of math, and is probably better understood by playing Kerbal Space Program.
[Relevant xkcd](https://what-if.xkcd.com/58/)
The short version is that the earth is spinning too. There’s a distance from the earth where you can be going fast enough sideways to “miss” the earth when falling, i.e., be in orbit, but be moving at the same speed the earth is turning at. It’s pretty far out actually.
We call that distance “Geosynchronous Orbit”, since things in that position, moving sideways like that end up appearing to stay directly above the same point on the planet.
There is, of course, a much longer version, and it has to do with the satellite’s orbital velocity synchronizing with the gravitational force of the earth such that there’s an apparent relationship between a spot on the ground and the satellite, but it involves a lot of math, and is probably better understood by playing Kerbal Space Program.
Grab on to a yoyo string and spin around really fast. Notice how the yoyo stays in the same place relative to your body (outward from your arm)? Geosync orbit is the same, except instead of a string holding the yoyo from zipping off into space it is gravity. The yoyo/satellite is still moving quickly, it just happens to be far enough out that it can both be moving fast enough to ‘miss’ the earth ats it falls _and_ stay in the same place above the earth.
Grab on to a yoyo string and spin around really fast. Notice how the yoyo stays in the same place relative to your body (outward from your arm)? Geosync orbit is the same, except instead of a string holding the yoyo from zipping off into space it is gravity. The yoyo/satellite is still moving quickly, it just happens to be far enough out that it can both be moving fast enough to ‘miss’ the earth ats it falls _and_ stay in the same place above the earth.
Grab on to a yoyo string and spin around really fast. Notice how the yoyo stays in the same place relative to your body (outward from your arm)? Geosync orbit is the same, except instead of a string holding the yoyo from zipping off into space it is gravity. The yoyo/satellite is still moving quickly, it just happens to be far enough out that it can both be moving fast enough to ‘miss’ the earth ats it falls _and_ stay in the same place above the earth.
If the earth would not be rotating there would be no geosynchronous orbit because then as you mentioned anything would fall down as it has zero orbital velocity. But as earth rotates once in 24h you can have something orbiting above the same spot on the surface.
Orbital speed depends on your height, the higher up, the slower sideways you need to go to stay in orbit, so any rotating planet has some syncronous orbit, its just higher or oowed depending on a days length and its mass.
If the earth would not be rotating there would be no geosynchronous orbit because then as you mentioned anything would fall down as it has zero orbital velocity. But as earth rotates once in 24h you can have something orbiting above the same spot on the surface.
Orbital speed depends on your height, the higher up, the slower sideways you need to go to stay in orbit, so any rotating planet has some syncronous orbit, its just higher or oowed depending on a days length and its mass.
If the earth would not be rotating there would be no geosynchronous orbit because then as you mentioned anything would fall down as it has zero orbital velocity. But as earth rotates once in 24h you can have something orbiting above the same spot on the surface.
Orbital speed depends on your height, the higher up, the slower sideways you need to go to stay in orbit, so any rotating planet has some syncronous orbit, its just higher or oowed depending on a days length and its mass.
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