Precession of the Equinoxes
Let us first understand what is precession. To understand this, understanding equinox is very important. Celestial equator and ecliptic intersect each other at a point. This point of intersection is known as equinoctial point. One of the point is known as Vernal Point and the other is known as autumnal point. These two points are also known as precession (Ayan). When Sun comes at these two points, then the day and night are equal.
These equinoctial points have retrograde movement. Like the way Rahu and Ketu move in the opposite direction, similarly, Vernal point moves back from its original position. That is why, this movement is also known as retrograde movement. The equinoctial point starts from the 0 degree of fixed Aries sign in the condition where precession (Ayan) is not there. Hence, precession is not included in this condition. Hence, the point without precession (Nirayan) is fixed.
The theory of point with precession (Sayan) is used to forecast future in the west. Their calender consists of planets with precession. But, the forecast of future in Indian astrology is done without precession (Nirayan). In India, astrologers of places like Maharashtra use the former method which is also used in the west.
The astrologers following the theory of point with precession (Sayan) add the degree of precession (Ayanamsha) to the planet to make it with precession (Sayan). On the contrary, astrologers following the point without precession theory exclude the degree of precession (Ayanamsha) from the planet and calculate the result.
The astrologers using any one of the method state it as appropriate. Apart from making predictions, these two methods are also used for other purposes.