Why do geosynchronous satellites have to orbit above the Equator?

Click For Summary

Discussion Overview

The discussion centers on the requirements for geosynchronous satellites, specifically why they must orbit above the Equator. Participants explore the implications of orbital planes, gravitational forces, and the definitions of geosynchronous versus geostationary orbits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that geosynchronous satellites must maintain a position relative to the Earth, leading to questions about the necessity of being above the Equator.
  • One participant explains that the plane of an orbit must pass through the Earth's center, indicating that only the Equator represents a latitude plane that fulfills this requirement.
  • Another participant suggests that while a satellite can have a 90° inclined orbit, it would not remain fixed in the sky, thus questioning the nature of geosynchronous orbits at different inclinations.
  • Some participants clarify that a geosynchronous orbit can be inclined, but a geostationary orbit must be equatorial to remain fixed above a specific point on Earth.
  • One participant raises a hypothetical scenario about the center of gravity being offset from the center of the Earth, prompting further discussion on the implications of such a condition.

Areas of Agreement / Disagreement

Participants generally agree that geostationary orbits must be equatorial, but there is some debate regarding the nature of geosynchronous orbits and the implications of different orbital inclinations.

Contextual Notes

Participants express uncertainty about the effects of gravitational forces on inclined orbits and the implications of hypothetical scenarios regarding the Earth's center of gravity.

question dude
Messages
80
Reaction score
0
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?
 
Astronomy news on Phys.org
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.
 
phyzguy said:
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?
 
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.
 
question dude said:
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.
 
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
 
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!
 

Similar threads

  • · Replies 36 ·
2
Replies
36
Views
8K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K