Which astronomer proposed the heliocentric model that challenged the geocentric view?

• A. Ptolemy
• B. Copernicus
• C. Aristotle
• D. Kepler

Answer: (B)

The key idea being tested is who first proposed a sun-centered model of the solar system that challenged the long-held geocentric view. Copernicus argued that the Sun sits at the center and the planets, including Earth, orbit around it. This reframing explains planetary motions more simply than a system where Earth is at the center with everything revolving around it. His work, On the Revolutions of the Heavenly Spheres, marks the beginning of the heliocentric shift, even though his model kept circular orbits and included epicycles, so it wasn't immediately accepted. Later astronomers, like Kepler, refined the model with elliptical orbits, but the foundational idea comes from Copernicus. Ptolemy and Aristotle upheld geocentrism, and Kepler built on Copernican ideas rather than initiating them.