Signs vs. astronomical constellations of the zodiac Nearly all astrologers, tropical and sidereal, agree that the ecliptic should be divided into twelve equal segments to form the zodiac; they differ on where the zodiac begins. Thus, most sidereal astrologers simply divide the ecliptic into 12 equal signs of 30 degrees but approximately aligned to the 12 zodiac constellations. Assuming an origin of the system in 786 BCE, this results in an identical system as that of the classical tropical zodiac, shifted by 25.5 days, i.e., if in tropical astrology, Aries is taken to begin at March 21, sidereal Aries will begin on April 15.