Western Astrology uses the tropical system of zodiac. There are two system of zodiac one is tropical and other is sidereal. For calculating the birth chart western astrologers use tropical system of zodiac which is 24 degree ahead of sidereal system of astrology based on sun sign position. Sidereal system is based on the position of fixed star spica or chitra nakshatra from which exactly 180 degrees opposite ashwini nakshatra falls which starts the zodiac belts. So most of the astrologers including famous astrologers like K.n rao,B.v raman and other well known astrologers uses nirayana system of astrology or sidereal astrology. western astrologers use tropical system of astrology which believes that 1st sign of aries start on 21st march according to sun position. Their believe lies on vernal equinoxes. Western Astrologers do not give importance to moon or moon sign while for vedic or hindu astrologers moon is the most important planet ,not sun.