Michael replied: "Ophiuchus."
After some discussion, it was determined that Michael was actually right.
Now, your astrological sign (or Sun sign) is the constellation the sun was in at the moment of your birth. Or at least, that's what it supposedly is.
However, a long time ago people got sick of trying to actually work out where the sun was at that time to determine your exact sign, so they decided to split the sky into twelve even sections, and name each section after the major constellations and leave it at that.
Of course after about 2000 odd years or so, this is even further out of alignment than it was when they originally did this, what with changes in the tilt of the earth, movement of the solar system, etc.
As a result if you really wanted to be technical, their are a total of 13 modern day Astronomical Constellations of the Zodiac. They are:
Capricornus - January 19 to February 15
Aquarius - February 16 to March 11
Pisces - March 12 to April 18
Aries - April 19 to May 13
Taurus - May 14 to June 19
Gemini - June 20 to July 20
Cancer - July 21 to August 9
Leo - August 10 to September 15
Virgo - September 16 to October 30
Libra - October 31 to November 22
Scorpius - November 23 to November 29
Ophiuchus - November 30 to December 17
Sagittarius - December 18 to January 18
Of course, this doesn't take into consideration that they'll be different depending on the exact location you are born at, the exact tilt of the earth at that point, etc, plus when you start getting really into it and talk about your other signs as well (Mercury, Mars, Venus, etc) they don't follow the same path through the sky as the sun. So if you take all of that into the equation, there are a total of 21 astronomical signs of the zodiac, the 13 listed above, plus Cetus, Corvus, Crater, Hydra, Orion, Pegasus, Scutum and Sextans.
I'm getting a copy of a piece of software from a friend that can show you the sky at a certain point in time so I can fiddle a bit with this. So, if anyone wants a full, astronomically correct reading, tell me your exact birthday (date and time) and location of birth. I won't interpret it for you, but I'll let you know where all the bits are. :)