Sidereal astrology is the practice by some western and all Indian astrologers of basing their study of the sky on the actual position of the planets.
Sidereal astrologers claim their approach is more in keeping with the ancient traditions of the subject. Until the middle ages all astrology was conducted using the sidereal approach.
Most astrologers in the North and South America and Europe base their study on a notional view of the heavens which does not match the actual present positions of the stars. The sidereal zodiac is used everywhere else.
About 2,000 years ago, the two approaches were in approximate agreement. However, the tropical zodiacal system assumes that the constellations are all the same size, which they are not.
The Sidereal system of astrology is based on the position of the belt of fixed stars, whereas the Tropical zodiac is based upon the position of the Sun in relation to the Earth. The first degree of the Sidereal zodiac is measured from a point 180 degrees opposite the star Spica, whereas the first degree of the Western zodiac occurs when the Sun reaches the position above the equator known as the vernal equinox. This is where the two systems differ greatly in their calculations in erecting charts.
Due to the peculiarities in the Earth's orbit, called the "procession of the equinoxes," the difference between the two systems is calculated at about 23 degrees.
The practice of Sidereal astrology has been in continuous use in India for thousands of years and in recent years has become increasingly popular in the West as well. This method gives clear indications about one's personality and personal proclivities, and also uses predictive methods which are useful for short or long range planning in one's life.The study of the twelve houses of the Sidereal horoscope reveals one's destiny in all areas of life.
Sidereal Astrology is more closely related to the actual constellations. Precession of the equinoxes moves the astrology signs forward through the years, so Sidereally, Aries begins in April instead of March. That is if you are a March Aries in Tropical Astrology, then you are a Pisces in Sidereal Astrology.