Gravitational/electromagnetic effect of planets on solar activity? Does the gravitational and/or electromagnetic influence of planets have any effect or correspondence to solar activities (e.g. solar flares/CMEs) - and if so, does the planetary position (where they are in their orbit in regards to distance from the sun) have an effect? How do we know? 
 A: This looks like a subject that gets plenty of crackpots excited. But there is some respectable, peer reviewed work out there if you can pick your way through the dross.
For example Stefani et al. (2016) have done some theoretical work, claiming that the 11.07 year cycle with which the tidal effects of Jupiter, the Earth and Venus line up, might excite a resonance in the $\alpha$ part of the $\alpha-\Omega$ dynamo. This resonance could lead to the solar magnetic cycle.
Another example is Abreu et al. (2012), who hypothesise a non-spherical tachocline (the seat of the solar dynamo) upon which a variable torque is applied by the planets. The Fourier transform of 9000-odd years of solar activity records shows a remarkable agreement with a Fourier transform of the planetary torque.
I cannot and do not vouch for any of thus work and they certainly have their critics.
One of the problems that any such hypotheses may have to address is that there does seems to be a complicated relationship between magnetic activity cycle period and rotation period in a substantial sample of solar-type stars (e.g. Broomhall 2017). Since the rotation period changes with age it is not clear then how the cycle period could have anything to do with planets.
