Quoting Fistalis, reply 22In this illustration the big one would be a star (the sun is a star for you aspiring writers out there) and the small one would be a planet. The + is the center of mass.
Well, you illustration look like these at http://en.wikipedia.org/wiki/Barycenter#Astronomy ... cute little theoric illustration... in reality, thing are a lot more complex with a lot of planet who don't rotate in sync...
The pic below show the solar system center of mass... sometine near the nucleus like in 1951 and 1990... and sometime way outside of the sun...
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Yes.. but a more complex illustration doesn't change anything. What in my post are you disputing? Notice your illustration doesn't show the movement of the sun.. and assumes the sun is stationary. Which muddles the facts.
Of course the center mass is going to fluctuate with movement of the sun and planets (aka said mass). Its not that the center of mass itself is moving but that the mass itself is changing position, altering where the center of mass is. But that doesn't change the fact that the sun and planets orbit the center mass.
Personally I think the illustration I chose was adequate for illustrating my point. Since the center of mass compared to the suns position isn't important when speaking of the fact that the sun and planets all orbit the center of mass.
A better illustration would be the suns position in relation to the center of mass.. showing how its orbit is effected by it. Rather than an illustration which assumes the sun is stationary. That particular illustration even gives the idea of the age old myth that the sun is the center of the solar system. Which technically speaking it isn't. While the illustration is technically correct.. it gives the wrong idea, which might lead aspiring writers to make bad assumptions and misinform everyone else.