That was Johannes Kepler.
He couldn't say why that should happen. But he was able to show that
if we assume the the sun is in the center of the solar system, and assume
that the planets revolve around the sun in elliptical orbits, and assume that
the farther a planet is from the sun the longer it takes to orbit the sun, then
that matches everything that we see the planets actually doing in the sky.
Then Isaac Newton came along, and wrote down a short, simple formula
for the force of gravity. And then he showed that IF his formula for gravity
is correct, then the planets MUST do everything that we see them actually
doing in the sky, and they MUST behave according to Kepler's laws.
Wotta guy !
