The tropical zodiac is based upon tropical time , or the apparent motion of the sun across the sky over the course of a year. The tropical zodiac fixes the position of the sun in the heavens at the northern hemisphere vernal equinox as the first point of the sign of Aries. The signs of the zodiac in tropical astrology are therefore currently divorced from the actual constellations of the zodiac. This is due to the Precession of the equinoxes. The tropical zodiac therefore uses a view of the heavens as seen from Earth approximately 2000 years ago when the northern hemisphere vernal equinox did occur within the constelation of Aries.

This is in contrast to the sidereal zodiac, which is based on the apparent motion of the sun against the actual constellations of the zodiac in the sky.

The tropical zodiac is largely exclusive to The Americas and western European astrologers.

Some western astrologers choose to use the sidereal zodiac and criticise the tropical approach as erroneous. This is a long running dispute within western astrology.