Whose heliocentric model is seen as the first step in the development of modern models of the solar system?
The heliocentricity observation is dated back to two millenniums ago, in the works of Aristarchus (3C BCE) and of Selucius (2C BCE). Copernicus (16C AD) made a heliocentric model..
16th century Copernicus was the first to make a heliocentric model with Earth circling Sun, very fast, and stars moving around, very slowly.
Foe graphic description of the model and more details: