Sidereal and tropical astrology


Sidereal and tropical are terms used to describe two different definitions of a year. In astrology, they refer to two different systems of ecliptic coordinates used to divide the ecliptic into twelve "signs". Each sign is divided into 30 degrees, making a total of 360 degrees.
While sidereal systems of astrology define the signs relative to the apparent backwards movement of fixed stars of about 1 degree every 72 years from the perspective of the Earth, tropical systems fix the vernal point or vernal equinox to 0 degrees of Aries and define the rest of the zodiac from this point. Sidereal astrology uses corrective systems known as ayanamsas to account for the precession of equinoxes, whereas tropical astrology does not use such measures. This has caused the two systems, which were identical around 2,000 years ago, to drift apart over the centuries.
Ayanamsa systems used in Hindu astrology include the Lahiri ayanamsa and the Raman ayanamsa. The Fagan-Bradley ayanamsa is an example of an ayanamsa system used in Western sidereal astrology. As of 2020, sun signs calculated using the Sri Yukteshwar ayanamsa were around 23 or degrees behind tropical sun signs. Per these calculations, persons born between 12th March - 12th April, for instance, would have the sun sign of Pisces. By contrast, persons born between March 21st - April 19th would have the sun sign of Aries per tropical calculations.