Nice image. And you contributors always bring out much more than I first realize is interesting.
As the Earth and Moon rotate around a center of mass, I assume that when the Moon is full, the Earth is always closest to the Sun (a local minimum, that is). If the Moon is full at apogee, then if I understand this, that must be a time when the Earth is swinging farther from the center of mass as well, so it is pushed closer to the Sun by the maximum amount that this effect ever produces. However, the Earth/Moon's orbit around the Sun is elliptical itself, and I am guessing that the eccentricity of the orbit is such that the regular perihelion of the Earth/Moon pair is a larger effect than the amount of the 28-day swings. Looking at Wikipedia: http://en.wikipedia.org/wiki/Earth's_orbit
I read that the Earth/Moon are much closer to the Sun in January, they say that in current times perihelion occurs around Jan 3. But that article is only discussing Earth, not really treating the Earth/Moon system, as far as I can tell. Anyway, they list perihelion at 147,098,290 km versus aphelion at 152,098,232 km, a difference of about 5,000,000 km.
So, here's what I'm thinking. If Moon's apogee occurs right at a full moon, just at Earth/Moon's perihelion, then that is the closest Earth ever gets to the Sun. A micro-moon coinciding with Jan 3 would cause the Earth to get closer to the Sun than any other time. But the Earth is only pushed closer to the Sun by it's distance from the center of mass of the Earth and Moon, so I would guess this is only a small boost to the 5,000,000 km effect of the eccentricity of the overall Earth/Moon system's orbit. As I read further, it appears that the center of mass of Earth/Moon is actually within the Earth. That's a surprise! So, the maximum variation all of this causes in Earth's distance from the Sun is going to be only about 4000 km.
- Anything grossly incorrect in the above? Let me know.
- Does the fact that Earth reaches perihelion during winter in the Northern Hemisphere make the North's winters any milder than the Southern Hemisphere's ?