Geosynchronous vs geostationary orbit: the simple difference
A geosynchronous satellite has an orbital period matching Earth’s rotation; a geostationary satellite is the special circular, equatorial case that appears fixed over one longitude.
A geosynchronous orbit has a period matching Earth’s rotation, approximately one sidereal day. A geostationary orbit is a special geosynchronous orbit that is circular and lies over the equator, allowing the satellite to appear nearly fixed above one point on Earth.
Why every geostationary orbit is geosynchronous
Matching the planet’s rotation period is the defining feature of a geosynchronous orbit. But an orbit can be inclined or elliptical and still have the same period; from the ground, the satellite may appear to move north–south or trace a loop in the sky.
For a geostationary orbit, the circular path and equatorial plane are essential. That geometry keeps the satellite’s apparent position almost constant, which is useful for communications and continuous observation of a region.
What this means for satellite services
A fixed-looking satellite can simplify pointing a ground antenna and can repeatedly view the same broad region. Other missions use different orbits because they need changing viewing angles, closer passes or coverage of higher latitudes.
The terms are often used loosely in headlines. Check the orbit description in the mission or space-agency source before assuming that any satellite described as geosynchronous is stationary in the sky.
Editorial note
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Frequently asked questions
Is every geosynchronous satellite stationary in the sky?
No. Only the geostationary subset appears nearly fixed above one longitude.