Who proposed the heliocentric model of the solar system?

• A. Johannes Kepler
• B. Nicolaus Copernicus
• C. Galileo Galilei
• D. Ptolemy

Answer: (B)

The idea being tested is who first proposed a sun-centered view of the solar system. Nicolaus Copernicus introduced the heliocentric model, placing the Sun near the center and describing Earth and the other planets as orbiting around it. This shifted away from the long-held geocentric view that had Earth at the center and used epicycles to explain motion. The heliocentric idea explains retrograde motion as a natural effect of Earth and other planets moving at different speeds around the Sun, rather than requiring complex additions to a Earth-centered system. Copernicus’ work laid the foundation for modern astronomy, and was later built on by Kepler, who described elliptical orbits, and Galileo, whose telescopic observations provided supporting evidence.