I had a pretty big fight with my sister today about horoscopes. She is a pretty strong christian, and believes in all kinds of other weird stuff and energies, and of course, I took a few physics courses so i know better. anyways, she thinks that people born on the same day must share a lot of things in common because... of the horoscope, and the constellations of the stars and all that. My argument was that the constellations of stars in the outer space can only affect us by gravitation and some electromagnetic radiation. Now since the radius of earth's orbit around the sun is so tiny relative to these distant starts, treating it as a point should be a very good approximation, and hence all effects on us from the outer space should be constant at any time of the year. I mean, it could be that something drastic is going on in the outer space that DOES affect life here, but can it have a period of exactly one Earth year? That sounds so implausible to me... Now if the horoscope has also ties to positions of sun/moon/other planets, i still can't see how gravitation could affect a human being, magically fixing his characteristics somehow... I mean, we are just a bunch of atoms, and we are always oriented in random ways with respect to the sun, or moon, etc. just by facing different directions, and we even have the effect of earth rotating on it's axis, so on average, any bigger effects like that should cancel out. Naturally though, neither she, nor my family understood anything about my argument, and they now think that i'm just weird that way. Anyway, it sparked my interest, is there some physical phenomena that could explain horoscope?