Now, people like to believe in Astrology, even just because it's amusing- never mind the people who take it seriously.
If there WERE a truth to it, could there be a rational hard-science reasoning behind it?
With this in mind a few years ago I set out to invent and explanation which did not go against science.
Here it is.
First, look at mammals as a whole. If you have trouble with picturing them, mammals are animals which have breasts. Dogs, cows, dolphins, mice, elephants, ferrets, gorillas, etc. In the big picture, MOST larger mammals breed once per year in order to properly be in tune with the seasons- we don't want a new baby in the middle of the snowy winter, or the drought season, etc.
So somewhere inside is a hard-coding for specific behaviors.
At some point in our evolution, humans were animals like this. It seems likely that we may have spent hundreds of thousands of years as such animals.
Now, I can't imagine that in a complicated creature such as a human that a behavior is just a switch, such as "you will dig a hole and live in it for three months now, because it's going to snow", but a suite of behaviors which support this need.
Adaptation and climate change may force such a behavior to fade, but perhaps the supporting activities aren't so completely removed. Such as, you don't need to dig the hole to live in anymore, but you still tend to go looking for nuts and feel like you need somewhere to store them, etc.
Now, back to the point.
If we were born at the same time of year for a very long period of time, then it's possible that the effect of this may still exist in our heads.
If there did exist a 'correct time' to be born, say in June, then you were supposed to be plunged into winter six months later. If you were instead born in December, then your body/subconcious is expecting snow at the wrong time- in June.
My idea is that being born at different grades away from this "original" birth time may cause similar personality traits in people. That is, the effect on your personality of thinking it's supposed to be snowy in June may differ from the effect on your personality of thinking it's supposed to be snowy in March.
Are the ideas pushed by astrology 'true'? No idea. Just fun with thinking.