There are many small small effects of backwards position of earth also called precession of the equinoxes, one of the major one is that the earth is now located differently in relation to the stars than it was in ancient times, such as the time of the Greek astrologer Ptolemy.
This means that the Vedic India astrology dates of the Sun's apparent "entry" into the different groups of stars of the zodiac are no longer the same as the dates given by traditional Western astrology.
Astronomically, the Sun does not really enter the constellation of Aries until around the middle of April, instead of the third week of March as in the Western convention. What this means, for the Vedic system, is that unless you were born around the 15th to the 20th of the month, your Sun sign will move back one whole sign.
Actually, all planetary placements will shift back by about 24 degrees, putting a lot of the Western planets in different signs and houses. Another distinction of Vedic astrology is that it tracks planetary cycles in relation to the Moon's journey through the night sky. Not only do Vedic astrologers have the 12 signs of the zodiac, they also have at their disposal an additional 27 Moon signs, called nakshatras. Still another difference between the East and West is that astrologers trained in the Indian technique have not just one chart to work with, but a set of 16 variations of the birth chart called the shodasavargas. The most important of these shodasavargas is the navamsa, which is one-ninth of a Sun sign, and is said to give more specific information.