In Would alignment of the planets cause catastrophe?, Cecil suggests that planetary alignments can be discounted because, even when planets appear to be aligned from Earth, they are typically spread across wide solar-centered arcs.
Now, just to play devil’s advocate here, if I did believe that the planets exerted a significant gravitational (or other more mysterious) effect on us poor hapless Earthlings, why would the solar-centered arc be at all relevant? Surely any summation of forces resulting from the alignment would be more sensitive to the Earth-centered arc. And isn’t a small Earth-centered arc exactly what we mean by “alignment” of planets?
In fact, if I really feared the gravitational effects of an alignment, I think I would be most concerned when a number of planets lined up with the Sun itself (solar-centered arc near 180 degrees if both inner and outer planets are involved) or perhaps when a number of (outer) planets were aligned at solar midnight.
I realize that planetary alignment fans might not want to hear about inverse square laws for gravitation (yecch - math!) and, if gravity isn’t the force they have in mind, it’s frustrating to try and debunk the completely unspecified. But I think the solar-centered arc argument is a strawman.