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?

Question

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

Answer 1

They are only above a single point on the rotation surface of the earth. Evey point on Earth except for the poles move because of earth rotation.

If you look at orbit it does not matter if Earth rotates or not, the orbital period for a given distance would be the same if Earth was not rotating. Geostationary orbit is just that the time of an orbit one around Earth is the same as it takes Earth to rotate once.

So both the point on Earth and the satellite move with the same angular speed around the center of the Earth.

The orbital period will be one sidereal day, that is one rotation of Earth relative to faraway stars. that is around 4 minutes less than 24 hours. The extra 4 hours per day is from the earth’s orbit around the sun, consider the moment of the sun during an orbit around the sun if the earth was not rotation relative to faraway stars.

4 minutes a day for 365 days are 1460 minutes which is proximally the same as 24 hours = 1440 minutes. The difference is because neither 4 minutes nor 365 days are exact

Because the orbit is around the center of the earth in a plane the point of earth it is stationary above also needs to move around the center in a single plane. Only the equator of the earth does that.

So geostationary satellites are always directly above the equator, if they was not they would move relative to the ground, the moment might just be north and south around the equator but it still moves.