What is the heliocentric model?

• A. The astronomical model that places the Sun at the center of the solar system
• B. The model that places Earth at the center
• C. A theory about planetary orbits
• D. A model that places the Moon at the center

Answer: (A)

The heliocentric model is the sun-centered arrangement of the solar system, where the Sun sits at the center and the planets orbit around it. This puts Earth among the planets circling the Sun, unlike earlier ideas that placed Earth at the center. By shifting the center of the system, it explains planetary motions more simply, such as the way planets’ positions change and why they can appear to move backward in the sky when Earth overtakes them in its orbit. Copernicus introduced this view, and later observations—like the phases of Venus and the moons of Jupiter—provided supporting evidence. So the defining idea is that the Sun is central and the planets, including Earth, revolve around it.