The astronomical zodiac actually contains 13 constellations – the 12 that we’re familiar with plus another one, called Ophiuchus.
Ophiuchus was deliberately left out of the original zodiac, over 2000 years ago, even though the Sun clearly passes in front of it after passing in front of Scorpius (commonly known as Scorpio) and before reaching Sagittarius. The reason for this is not known, but it may be because ancient astrologers wanted to divide the 360 degree path of the Sun in a mathematically pleasing way – 12 equal parts, each one of 30 degrees.
However the true boundaries that divide the constellations, as described by the International Astronomical Union, are far from equal. For example Ophiuchus is behind the Sun for a full 19 days of the year. That’s 12 days more than its neighbour, Scorpius.
So if you were born between 30 November and 18 December, why not claim yourself a totally new star sign?