Astrology and physics
So, I have a friend who is very strongly into astrology - the idea that based on the alignments of stars and planets, one can make predictions about someone’s personality, career and even future. Unfortunately, astrology is one thing I absolutely don’t believe in. For example, I would be willing to consider the possibility that palmistry has some basis - that your palms reflect your the plan you set yourself for this life. Although highly unlikely, it could at least be made to make logical sense in a “science fantasy” style book. I actually learned some palmistry many years ago, and have done some palm readings - but I think it’s more the Forer effect (which I’ll come back to tomorrow) plus some basic genetics that’s at play.
Anyway, I can’t see any logical basis for astrology. First up, why should the planets and stars have any affect on us? Scientifically, there are a few possibilities. Let’s first consider possible physical effects they could have on our genes or our minds.
The most measurable effect is the light reaching us, including radio waves, infrared, etc. But this light negligible compared to that reaching us from the sun, or from lightbulbs for that matter, so seems unlikely to have any physical effect.
Another option is gravity - perhaps the subtle pull of the universe can cause astrological effects. However, some high school physics comes into play. The gravitational force between two objects is measured in Newtons, and is given by the product of the two masses divided by the square of their distance, and scaled by the gravitational constant G = 6.67300 Ă— 10-11 m3 kg-1 s-2. It’s a very small effect, but it’s cumulative - so the force between two apples might be tiny, but put enough apples together (e.g., a planet!) and you have something significant. Let’s consider the force on a 70kg person due to the nearest start, Alpha Centauri (yes, I know it’s really Proxima Centauri that’s closest 
Its mass is roughly comparable to the sun’s, and is a distance of four light years away. Using Google, we quickly see that the force from this star is about 6×10-12 Newtons - one trillionth of a Newton. For comparison, the force on that person from Earth’s gravity is about 700 Newtons - we’re talking about a change in force of a trillionth of a percent! Hardly noticeable, one would think.
What about the planets? They’re closer, though lighter, and so should have a bigger effect. Let’s take Jupiter - it’s at a distance of about 588 million kilometres, and weighs in at 2×1027 kilograms. This gives us a force of 2 x 10-5 Newtons. Much larger, but still much smaller than the 700N from Earth! But maybe it’s enough to make a difference? Well let’s try something. Let’s consider the force from a standard, 5000L water tank. Let’s imagine it’s got a diameter of 2m, so when you’re right beside it, you’re standing about 1m from its centre (strictly, oh learned physicists, it’s not a point source, but for the purposes of this calculation…!) 1L of water weight 1kg, so calculating the force on our person, we find it’s again 2×10-5 Newtons. (I swear, this was only chance - I honestly didn’t choose special numbers!!!) That means your water tank is causing as much effect on you when you stand beside it as Jupiter does - and far more than all the stars in Taurus! Now, imagine standing beside a house - or a skyscraper - or a big rock. If gravity were responsible, as is sometimes claimed, these should also be included!
Obviously, the gravity argument is relatively simple - more complex arguments include subtle effects on our sun, in turn producing subtle magnetic field effects on Earth, etc. But I suspect that similar calculation would show that the time and space variation of these fields isn’t anywhere like as strong as the corresponding variation in someone’s astrological chart would be. I also suspect that local deposits of iron ore etc would produce comparable changes, if indeed these changes occur at all.
Therefore, I think we’re running out of options for a physical effect from these stars on us. Yes, together all these stars do have an effect - they hold us in our orbit around the galaxy, for one. But we need something that is so specific that it can distinguish between the minute, longitude and latitude of your birth. Therefore if anything’s going on, it’s got to be either spiritual or psychological - which I’ll come to tomorrow, as I think this is enough for one post! In particular, I’ll point out some of the studies for and against - and provide some useful links!
It is good that you clarify what astrology is about; I was going to answer that astrology is very good to predict the sequence of seasons (most probably its original goal) and some weather predictions (depending of the visibility of stars you can assess the water content and temperature of the atmosphere).
Now, I think that a “cold reader” futurologue can take some advantage of knowing the date of birth of a person. For a trivial example, if you are Leo (born in August) most probably your school companions were not in your birthday celebration (no they hated you, but holidays). Secondly, if the cold reading is done upon a person that believes astrology, then the reader and the, er, victim, have a common language that can be used to detect emotions or body signals; it is an extra channel of information. This is similar to Tarot reading, the “reader” must put attention to the reactions of the person as cards are shown. Sometime
Astrology is used also as a language convention during mating, er, flirting. It is a polite way of requesting information from the other person by simulatiog you are “checking the stars”. It can also be used as a “pad conversation” to fill the vacuum while the couple is interested more on body signals than in speeches.