Heard a story on NPR that was discussing the problem with the 12 sign zodiac. In short your sign should be determined by what constellation was behind the sun on the day of your birth.
In the latter half of the year there is a small problem. The sun isn’t in front of Sagittarius from about November 29/30 to the middle of December. It’s in front of Ophiuchus.
But 13 bring an unlucky number, Ophiuchus got the boot.
Not that I believe any of this shit matters, but if you are interested for the sake of knowledge, here is some info.