Understanding the Earth-Moon Center of Mass and Its Effects on Lunar Orbit

[dimensionless]

Does the center of mass between the Earth and the moon follow an elliptical path around the sun? Does it wobble a little bit?

 

[pervect]

The exact path of the center-of-mass of the Earth-moon system is very slightly perturbed from an ellipse by the gravitational attraction of the other planets. However, it is very close to an ellipse because this perturbing influence is very small.

 

[Homer Simpson]

Wouldnt the CoM between Earth and Moon wobble each month (or moon cycle) as it follows the elliptical path caused by the moon revolving once around the earth??

 

[dimensionless]

I know that the center of mass would be constant if they were both just orbiting each other.

Could the sun perturb this?

 

[D H]

Wouldnt the CoM between Earth and Moon wobble each month (or moon cycle) as it follows the elliptical path caused by the moon revolving once around the earth??

No, because the Earth is also orbiting about the Earth-Moon CoM.

 

[Homer Simpson]

No, because the Earth is also orbiting about the Earth-Moon CoM.

The moon doesn't orbit around the earth, rather the Earth and moon orbit around
their mutual center of gravity located somewhere within the surface of the
earth.

http://72.14.207.104/search?q=cache...+center+of+mass+of+earth+and+moon+orbit&hl=en

I just learned something totally new to me.

 

[Homer Simpson]

Sorry to butt in with my own question, but can you explain this? (Not the actual tides part, but how it causes only one side of the moon to face earth. I always thought this was just a fluke, that the moon revolves once on its own axis for every one rev around the earth. Thinking about it, that would have to be one precise fluke!)

Have you ever heard the term the 'far-side' of the Moon? Because of the effect on the Moon of tidal forces due to the Earth, the same side of the moon always faces the Earth. The rotation period and the orbital period of the Moon are the same. Therefore, Earth-bound observers can never see the 'far-side' of the Moon. Tidal forces cause many of the moons of our solar system to have this type of orbit.

I would guess that the CoG of the moon is off center, closer to the Earth/Moon CoG due to the bulging effect of the Earth on the moon.

http://www.windows.ucar.edu/tour/link=/the_universe/uts/moon1.html&edu=high

Is there any good net sources for general learning on this stuff you would suggest?

 

[D H]

Sorry to butt in with my own question, but can you explain this? ... I would guess that the CoG of the moon is off center, closer to the Earth/Moon CoG due to the bulging effect of the Earth on the moon.

Is there any good net sources for general learning on this stuff you would suggest?

While the Moon does have some rather high non-spherical mass concentrations, it is primarily the second zonal harmonic (the "J2" term) that leads to the Moon's tidally-locked revolution. The second zonal harmonic by itself does not result in an off-center center of mass.

Google "gravity gradient torque".