The geocentric model was the belief in ancient times through the 17th century that the Earth was the center of the known universe and all other celestial bodies in the sky (the Sun, the planets, and other stars) revolved around it. This seemed a logical fit due to the fact that other bodies travelled across the sky in regular patterns and it also fit with religious dogma that ruled the day. The heliocentric theory is the modern theory that the Sun is the center of our solar system and the Earth and the other planets revolve around it in elliptical orbits. Furthermore, we now know that our solar system orbits the center of our galaxy along with all of the other stars in it. The heliocentric theory was first mathematically developed in the late 16th and 17th centuries by astronomers like Copernicus and Kepler as more advanced telescopes were invented and the mathematics of orbiting bodies more fully understood. Still, it took many years for the heliocentric model to gain acceptance due to widespread resistance, particularly from religious groups.