Astronomy Practice Exam 2025 - Free Astronomy Practice Questions and Study Guide

The geocentric model was the dominant astronomical theory prior to the widespread acceptance of the heliocentric theory, which posits that the sun is at the center of the solar system. In the geocentric model, the Earth is considered the center of the universe, with all celestial bodies, including the sun, moon, and stars, orbiting around it. This perspective was widely supported by ancient philosophers and astronomers, such as Ptolemy, whose work described the motion of planets and stars in a way that fit the geocentric framework.

The heliocentric theory, primarily developed by Copernicus and later supported by the observations of Galileo and Kepler, revolutionized this understanding by placing the sun in the center and explaining planetary motions more accurately. The transition from the geocentric to the heliocentric model marked a significant shift in astronomical thought, leading to the modern understanding of the universe's structure.