  By numerically solving the mass distribution in a rotating disk based on
Newton's laws of motion and gravitation, we demonstrate that the observed flat
rotation curves for most spiral galaxies correspond to exponentially decreasing
mass density from galactic center for the most of the part except within the
central core and near periphery edge. Hence, we believe the galaxies described
with our model are consistent with that seen through the eyes of Newton.
Although Newton's laws and Kepler's laws seem to yield the same results when
they are applied to the planets in the solar system, they are shown to lead to
quite different results when describing the stellar dynamics in disk galaxies.
This is because that Keplerian dynamics may be equivalent to Newtonian dynamics
for only special circumstances, but not generally for all the cases. Thus, the
conclusions drawn from calculations based on Keplerian dynamics are often
likely to be erroneous when used to describe rotating disk galaxies.
