Is there a battle between astrology and science?

The law of gravity is readily recognized and easily tested.  The force that gave rise to the expression, "whatever goes up must come down" has indeed undergone extensive scientific testing and is largely considered to be one of the most fundamental forces in all of nature.  The very pull of it can be felt as you read these words as you are held to your chair or the floor rather than floating around like a helium balloon.  Given this, is it possible for the gravitational forces from the planets to give rise to meaningful predictions from astrology?

The gravitational force of the sun and moon are what gives rise to tides.  It is the gravitational pull of the sun which keeps the earth in orbit preventing our planet from sailing off into empty space.  It is gravity that keeps ours and other solar systems in the galaxy bound together which in turn provides us with all the stars that we can see with our naked eye. 

Although the planets are also bound to the sun, they have a gravitational effect on us that is so small, it is too small to even measure.  To put this in some perspective, a few comparisons might be useful. Because the earth is not perfectly spherical but rather flattened at the poles (due to the earth's rotation), gravity gets a little stronger as you get closer to the north or south poles.  The difference in gravitational strength from the poles to the equator varies by as much as 0.5%.  Climbing a tall mountain can give more than a 0.1% difference in gravitational strength.

When it comes to the planets, the situation becomes very different and much, very much smaller.  Standing next to a 5,000 lb pickup truck will provide a gravitational force more than 100 times stronger than that from Pluto on you.  Standing next to another person would give a similar gravitational force as the planet Mars at its closest location to us. 

The largest effect from any planet on us at its closest position to the earth would be Jupiter, and even that would be around a millionth of a single percent difference.  This would not be quantifiable with any accelerometer on earth by a very long shot. Saturn would be 10 times weaker than Jupiter and Venus even ten times weaker than that.  All of the other planets have much smaller effects and even that is when they are at their very closest to the earth, completely aligned with us and the sun.

Appealing to gravity to attribute cause and effect on people could work from a placebo effect.  In this sense, if you are told you will make important decisions and you believe it, you might see all your decisions as important (or vice versa).  If you are told you will be making changes or staying the same or whatever and you emphasize those aspects in your day or choose to see them that way, you can convince yourself of their validity.  If one chooses to ascribe a spiritual significance to these things, then the options just expand from there.

This is not to say that there is no spiritual significance one could obtain from evaluating the heavens, even the bible says that, "God said, "Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs and seasons, and for days and for years;"" (Gen. 1:14).  As a scientist, I generally only quantify what is predictable, observable or reproducible.  The gravitational effects from the planets are in a very real sense, a negligibly small contribution from the vast array of larger gravitational effects in our every day environment.

One might try to argue that the planets can affect us through the magnetosphere or some other undiscovered mechanism.  Obviously I could not assess an undiscovered mechanism, only those properties that are understood and characterized.  So whether the Christmas star was a comet, a planet, a star or something else altogether, the effects of gravity are on the other hand, very well known.   If anyone were to make a prediction that the gravitational force from any of the planets have a noticeable effect on us is not something any modern scientific community would consider, "scientific".  

Care must always be utilized in a belief system to avoid seeing what you want to see or convincing yourself that how you want things to be is really the way they are.