Effect of Moon's Orbit on the Earth
Most recent answer: 11/14/2014
- Chuck Crisler (age 58)
Windham, NH, USA
The Moon does have an effect on the Earth's orbit, just as you suspect. The main effect would be there even if there were just the Earth and Moon, without a Sun. The combined Earth-Moon system rotates around its center of mass. Since the Earth is more massive than the Moon, by about a factor of 80, that's not too far from orbiting around the Earth's center, but it's far enough to be a major effect. The center of mass is still inside the Earth, but closer to the surface than to the center.
That's the first big effect. It leads to additional small effects. Since the Earth is making a monthly orbit around that center of mass point, it's also moving closer to and farther from the Sun. Since the Sun's gravitational field gets weaker farther from the Sun, that makes an additional small effect on the orbits. You have to add up all the little effects like that to get very accurate predictions of the orbits.
Mike W.
(published on 11/14/2014)