Orbital speed and moons

[Kertech]

Does the earth move faster round the sun when the moon moves in the direction of said orbit and slow down when the moon is going in the opposite direction? I know very little about orbital mechanics (save what kerbal has taught me (and planets are on rails!) )

[Steel]

Yes, but not noticeably 

[Shpaget]

Earth and Moon orbit around their barycenter which is around 4700 km from the center of the Earth. That means that the perimeter of the Earth's orbit is around 30 000 km. With Moon's orbital period of 27 days, we get Earths orbital speed (around barycenter) of around 46 km/h. 

Compare it to around 30 km/s of orbital speed around the Sun. There is a change, but not significant.

[Snark]

What the two previous posters said.

Also, you've got it backwards: the earth moves (very very slightly) slower when the moon is orbiting in the same direction as the earth's orbit around the sun, and faster when it's opposite.

[lajoswinkler]

Earth moves around the Sun on a line called cycloid because of the reasone explained in previous posts.