Two thousand years ago the night sky looked completely different, and so when you get right down to it, the Greek conceptions of star signs as related to birth dates are grossly inaccurate for today's day and age. It's called the Line of Procession: back then the sun didn't set in Taurus, but in Gemini. A September 24 birthday didn't mean you were a Libra, but a Virgo. And there was a thirteenth zodiac constellation, Ophiuchus the Serpent Bearer, which rose between Sagittarius and Scorpio for only four days. The reason it's all off kilter? The earth's axis wobbles. Life isn't nearly as stable as we want it to be.