A theory has been kicking around for a while: that as the planets orbit the sun, the changing gravitational fields cause the sun's behavior to change. This in turn might influence things like the sun's radiative output.
This isn't too terribly far fetched: after all, the sun is a fluid, and presumably the gravty of the plabets must have some influence on it. the question always was: how much.
A new paper claims that the effect is too small to be noticeable. You can find a link to the paper below: