of course, the original, best, and still ultimate, still useful taxonomies of human personalities are those described by astrological symbol systems. (Because there's so much bullshit online about astrology, I've had to go to wikipedia for the basics. Salt to taste.)
Okay, so as far as I can tell, the twelve constellations of the zodiac are the constellations that form a perfect circle around the Earth, so that when our planet turns, the zodiac signs are always in the middle of the sky (or rising or falling on either side along a central line). So, "your sign" (baby) is the sign of the zodiac in which the sun falls on the day on which you're born. I don't know what this means. Presumably, it means the sign that is in the center of the sky (and not rising or falling) on your birthday.
So your sign describes personal characteristics. It seems these personalities we like to use astrology to describe are based on convergences: this sign has this element, that aspect, and the other quality. Or something. Each of these (aspects, elements, etc.) carry with them characteristics. Combine all of these characteristics, and you can extrapolate a unique personality for each sign.
In addition, each visible planet and the moon also fall into signs on the day of your birth. Because days are determined by the sun's movement, the exact time of your birth on that day can change the position of the planets or the moon. The planetary and lunar signs also affect your personality in certain ways, so to determine your personality, the astrologer would have to choose the set of characteristics determined by your sun sign and all the rest, and then calculate and interpret their impact on your overall personality.
Then there's Chinese astrology, in which not only the 12 animals of the year in which you are born are important.
These yearly cycles represent what others perceive you as being: while a person might appear to be a Dragon they might actually be a Snake internally and an Ox secretively. Combined with 5 elements, this makes for 8640 combinations (5 elements, 12 animals, 12 months, 12 times of day). The inner animal is assigned by the month of birth. This dictates your love life and inner persona and is critical to a proper understanding of your compatibility with other signs. It may be considered what the individual wishes to become, or believes to be their true self. The secret animal is determined by exact time of birth and is your own true sign which your personality is based on. It is important to compensate for daylight savings or any clock adjustment performed by your country, as it is mapped according to the sun's location and not the local time.
This gets very complicated, so complicated, in fact, that one can suspect that a person's birth signs can be tweaked to mean pretty much anything. Which is why I've always respected astrology as a way of advising people---and probably why astrology is still so powerful in our culture. The astrologer isn't someone who understands how the stars affect us; the astrologer is someone who employs a woo-woo vocabulary to help her client understand himself better. "When the moon is in the seventh house and Jupiter is aligned with Mars" basically means "get your shit together before you lose momentum," or something like that. Well, imo.
Anyway, I think it's fascinating that 12 seems to be the magic number for personalities. Magic numbers are: 3 (very magic), 4 (elements), 7 (seventh sons, etc.), 8 (musical scale), 10 (counting), and 12, for different things, but 12 tends to be a natural cycle number and a human number (12 months, 12 jurors, 12 doughnuts). While we count things in groups of ten, and estimate larger numbers in tens (hundreds of, thousands of, millions of) we still estimate smaller numbers in twelves (dozens of, not tens of). It seems that 12 is the largest number of discrete identifiable units that we can maintain overview of. It's perfect for personalities, because we can fit personalities into twelve categories without feeling constrained, but we can still remember all twelve categories.
Someday, maybe soon, I'll write a cycle of 12 stories, each one driven by a character typical of one of the astrological signs. The question is: do I use the western or the Chinese system? I should probably do a little research first and figure out if the 12 western signs match up with the 12 eastern ones, or if they're divvied up differently.