Vedic astrology uses primarily the sidereal
zodiac (in which stars are considered to be the fixed background against which
the motion of the planets is measured), whereas most Western astrology uses the
tropical zodiac (the motion of the planets is measured against the position of
the Sun on the Spring equinox). This difference becomes only noticeable over
time, after the course of several centuries, as a result of the precession of
the equinoxes. Synchronically, the two systems are identical, with just a shift
of the origin of the ecliptic longitude by about 22 degrees or days, resulting
on the placement of planets in the previous sign in Western charts about 80% of
the time.