Universal Gravitation is a theory that everything in the universe is attracting everything else.
Newton's law of universal gravitation can be described as follows:
m1 x m2
F = G ────────
F is Gravitational Force
G is Gravitational constant
m1 is mass of object one
m2 is mass object two
r is the distance between the objects' centers of their masses
Be not afraid! All we are trying to do here is figure out the force of gravitational pull (F) between two objects (m1 and m2), and the above formula allows us to do just that.
The fascinating thing about this, is that theoretically, there is no limit as to how far this gravitational pull can extend; let's imagine an empty hypothetical universe and put two atoms 1,000,000 light years apart. Given that gravity propagates at the speed of light, after a million years these two atoms will start to influence each other, and given enough time will eventually come together.
This is analogous with putting two marbles on a stretched piece of fabric and watching them roll towards each other.
Fabric, unsurprisingly representing the fabric of space time continuum.
Armed with this knowledge, you can now argue that planet alignment DOES indeed have an affect on us mere humans, albeit a less mythical one in this case.
If you're reading this prior to FLT communication being invented, that means that you have already been affected by my gravitational pull