Why do geosynchronous satellites have to orbit above the Equator?

[question dude]

I get that they have to be at the same position relative to the earth

but why is it that they have to be specifically above the equator?

thats the sense I get from the textbooks, they all seem to emphasize the satellite being above the Equator

can't you have a geosynchronous satellite directly above Canada for example?

 

[phyzguy]

The plane of an orbit always has to go through the center of the Earth, since gravity is pulling the satellite towards the center. The only latitude plane that goes through the center of the Earth is the Equator.

 

[question dude]

The plane of an orbit always has to go through the center of the Earth, since gravity is pulling the satellite towards the center. The only latitude plane that goes through the center of the Earth is the Equator.

but can't you have a geosynchronous satellite orbiting in a non-latitude plane?

 

[Bandersnatch]

Imagine an orbit that is the extreme case of being 90° inclined, i.e., going over the poles.
You should see that even though the period of revolution of the satellite is the same as the period of rotation of the planet, the satellite does not stay in the same place on the sky.

All orbits with inclination between 90° and 0° will show the same effect, with diminishing magnitude. Only the extreme case of 0° keeps the satellite apparently motionless.

 

[Nugatory]

but can't you have a geosynchronous satellite orbiting in a non-latitude plane?

If you do it won't be geosynchronous. It will complete one orbit in 24 hours, but only if it's in the equatorial plane will it exactly match the one rotation in every 24 hours of the point on the Earth directly below it.

 

[jbriggs444]

It is perfectly possible to have a geosynchronous orbit that is inclined with respect to the equator. A polar geosynchronous orbit is possible.

The term geosynchronous means that the orbital period is the same as the rotational period of the earth.

It is not possible to have a geostationary orbit that is inclined with respect to the equator. Only equatorial geostationary orbits are possible.

The term geostationary means that the orbit keeps the satellite fixed above one point on the surface of the earth.

http://en.wikipedia.org/wiki/Geostationary_orbit
http://en.wikipedia.org/wiki/Geosynchronous_orbit

 

[Mazin Nasralla]

I was trying to figure this out too. But I got it as soon as I came across your explanation.

It's impossible to have a geostationary orbit above any other plane than the equator because the satellite would experience a force towards the Earth's centre taking it away from it's geosynchronous orbit. Of course a plane could do it but not an object in free-fall.

What if the centre of gravity is slightly out from the centre of the Earth? Presumably that's a small difference

Thanks for posting that even if it was quite some time ago. I expect quite a few people will have the same question. I don't think its immediately obvious. You need a sphere and then you can see it

I hope I have understood this correctly!