When the sun is less massive than the Earth, planetary and stellar bodies have gravitational relationships with each other that have the same relative proportions, but at a different scale.
Relative Quantities are not the Quantities
Sir Isaac Newton (1642-1726)
Newton's bold guess was that gravity is a property of mass. However, the proportional relationship between mass and gravity only measures the observed effect of gravity, it doesn't reveal its cause.
Sir Isaac Knew Tons
Sir Isaac Newton was fully aware that we could use words to define phenomena which were in fact unknown. Words are defined by what we use them for. It's a sublimely subtle form of induction.
Effect and Cause
Why are planetary orbits elliptical? We've considered this as an example of how to understand frame of reference, but Newton supposedly solved this problem mathematically in Principia Mathematica: