Many
ancient cultures have contributed to the development of Astro Physics.
Some examples are
The Saros cycles of eclipses discovered by Egyptians
The classification of stars by the Greeks
Sunspot observations of the Chinese
The phenomenon of Retrogression discovered by Babylonians
In this context the Indian contribution to Astro Physics ( which includes
Astronomy, Maths and Astrology ) is the the development of the ideas of
planetary forces and differential equations to calculate the geocentric
planetary longitudes, several centuries before the European Renaissance.
Natural Strength is one of the Sixfold Strengths, Shad
Balas and goes by the
name Naisargika
Bala. It is directly proportional to the size of the celestial bodies
and inversely proportional to the geocentric distance. ( Horasara ).
Naisargika Bala or
Natural Strength is used to compare planetary physical forces. When two
planets occupy the same, identical position in the Zodiac at a given instant
of time, such a phenomenon goes by the name of planetary war or Graha
Yuddha,happening when two planets are in close conjunction. The Karanaratna written
by Devacharya explains that the planet with the larger diameter is the victor
in this planetary war. This implies Naisargika
Bala.
The Surya
Siddhanta says "
The dynamics or quantity of motion produced by the action of a fixed force to
different planetary objects is inversely related to the quantity of matter in
these objects"
This definition more or less equals the statement of Newton’s second law of
motion
M = Fa
or
a = F/M
So it strongly suggests that the idea of planetary mass was known to the
ancient Indian astronomers and mathematicians.