The orbits of the Moon and of the principal planets also lie entirely within the zodiac. These s no longer correspond to the astronomical constellations in which the Sun actually appears.
There is so much more to this field than the run-of-the-mill, brief-ish horoscopes you read on a monthly, weekly, or daily basis. Of course, the most fundamental aspects of astrology are still the 12 Sun s a. However, if a person was born on a day when the sun switches s, their sun will be determined by the zodiac that the sun was in at the exact time of their birth. There's tons of complexity to the chat of these s, as zodiac as the rest of the universe.