We have said in our columns that the Indian astronomers said that the planets revolve around a point different from that of the Earth and Indian Astronomy is heliocentric.
The above diagram depicts the Eccentric Theory and Reduction of the longitude of the planet to the heliocentric coordinate system ( known as Manda Kriya ).
In the above diagram
The angle NAP = Manda Kendra or Mean Anomaly
The Circle A is the mean orbit of the planet
The Circle B is the true orbit
The mean planet moves on the mean orbit, known as the deferent.
When the planet is at N in the mean orbit, he is at M in the eccentric and this is called Mandoccha ( Aphelion ).
When the planet is at R in the mean, he is at S in the eccentric.
M and S correspond to Apogee and Perigee in the case of Manda Phala correction ( otherwise known as the Equation of Center ).
When the planet is at M in the eccentric, the position of the true planet coincides with N, the mean planet and so the Manda Phala correction is Zero.The Equation of Centre at both perigee and apogee becomes zero.
When the Mean Anomaly lies between 0 and 180 degrees, the Equation of Center is negative and this is known in Vedic Astronomy as Meshadi Rinam, Rinam meaning minus. And when it is between 180 and 360, it is additive and it is known in Indian Astronomy as Thuladi Dhanam, dhanam meaning additive.
Anomaly has been defined in Western Astronomy as the angle between position and perihelion. Manda Kendra here is the angle between Position and Aphelion, aphelion being mandoccha. The term manda explains that planets move slower at Aphelion !