Which model centers the Sun in describing planetary motions?

• A. Geocentric model
• B. Heliocentric model
• C. Ptolemaic model
• D. Aristotelian model

Answer: (B)

Placing the Sun at the center of the model means using a Sun-centered reference frame for planetary motions. The heliocentric model does exactly that: the Sun sits at the center and planets, including Earth, orbit it. This arrangement naturally accounts for why inner planets orbit faster and why outer planets take longer, and it explains retrograde motion as a result of Earth overtaking other planets in its orbit, without needing excessive constructs. By contrast, geocentric ideas keep Earth at the center and rely on epicycles or nested spheres to fit observations, which adds complexity and doesn’t align with a Sun-centered view. The Aristotelian approach is also geocentric, emphasizing a central Earth with surrounding celestial spheres. So the model that centers the Sun in describing planetary motions is the heliocentric one.