What is the logic behind Ayanamsa in Vedic astrology?

What is the logic behind Ayanamsa in Vedic astrology?

Sudheer Kumar · 

Why are there so many variations in Ayanamsa? Why is research in this area so elusive?

Ayanamsha is a kind of correction factor.

To measure the position of any planet, we have to define a starting point/origin in space.

In Astronomy, the starting point is defined as the intersection of the Earth’s equatorial plane and the plane of the Earth’s movement around the Sun in the celestial north pole. We also call it the First Point of Aries, its appropriate name being Vernal Equinox.

Till this point, I hope everything is clear. When we measure the planetary position in this system, we call it Tropical Astrology.

Earth has three different types of motion. First, two motions are rotation on its axis and revolution around the sun.

There is a third type of motion, which is the wobbling of the Earth, and it is due to a slight asymmetry in the Earth’s shape. The below picture is displaying the entire motion in 2–3 seconds, but it moves only by 50′’ in a year. It is a very slow movement.

Due to this movement, the first point of Aries or the reference point itself is shifting every year by some degree.

Ayanamsha is an attempt to define the starting point of the First Point of Aries by applying the right correction factor.

In Vedic astrology books, there are a lot of debates on this point; it is usually done by fixing a star as a reference point. Varahamihira, in one of his books, quoted the position of a star in Rashi at a particular time. We measured the position of the star through the tropical system and then estimated the value of Ayanamsha from the quoted position in the book. We call that star Spica/Chitra. Lahiri is based on this.

There is another problem: this movement is not linear, which means some years it changes by 50′’ and in some years it moves 1′. So to fix this, we started taking the true position of Spica as per the Tropical system every year and then deducting it from a reference point in our quoted textbook. We call this method True Chitra/True Lahiri.

Once we find the value of Ayanamsha, we have to subtract it from the positions of the planet in the Tropical System.

There is more to this; you can read it online.

I prefer True Chitra/True Lahiri instead of the pure Lahiri system.

https://www.quora.com/What-is-the-logic-behind-Ayanamsa-in-Vedic-astrology-Why-are-there-so-many-variations-in-Ayanamsa-Why-is-research-in-this-area-so-elusive