Mr Plait’s comments on relative gravity are correct, but this does not prove zero planetary effect. As noted at Science and Astrology , little Pluto, by dint of nothing more than gravity, has moved 100 million teralitres (km3) of earth water since the dawn of time, assuming that all the water of earth is moved each day by the moon’s gravity. If we assume just the top four metres of earth ocean is moved each day by the moon, Pluto gravity has moved 100,000 teralitres of our ocean. Over time this is a big effect. Uranus has a tidal effect on earth about 80,000 times bigger than Pluto, so by this calculation Uranus has moved eight billion teralitres of our ocean by tidal effect, six times the total ocean volume.

The issue here, in thinking through a conceptual reason for the observed statistical anomalies in lunar/planetary rain cycles, is that these tiny effects are permanent, in earth terms, and so present a rhythm which has been amplified and entrained by constant repetition over the fifty billion times the moon has orbited earth, within the constant presence of the rest of our solar system.

My hypothesis is that these tiny planetary gravitational effects are like a weak net cast over the earth, to which each point on earth aligns each diurnal rotation. Furthermore, during alignments (eg Moon –Jupiter) these weak nets reinforce each other, like musical notes in harmony. The nets cast by the Moon and each planet reinforce each other positively at conjunction and opposition, and negatively at square, as shown in full and neap tides caused by gravitational reinforcement of moon and sun (diagram at http://en.wikipedia.org/wiki/Tide).