The heliocentric theory, also known as the heliocentric model or heliocentrism, is a scientific model of the solar system in which the Sun is at the center, and the planets, including Earth, orbit around it. This theory stands in contrast to the geocentric theory, which was the prevailing model in ancient times and posited that the Earth was at the center of the universe, with celestial objects, including the Sun and planets, moving around it.

The key features of the heliocentric theory are:

1. Sun-Centered: In the heliocentric model, the Sun is considered the central and stationary body of the solar system, around which all the planets, including Earth, revolve.

2. Planetary Orbits: The planets, including Earth, move in elliptical (oval-shaped) orbits around the Sun. These orbits were described mathematically by Johannes Kepler in the early 17th century.

3. Earth as a Planet: Heliocentrism places Earth on an equal footing with other planets in the solar system, all subject to the gravitational influence of the Sun.

4. Motion Explained: Heliocentrism provided a simpler and more accurate explanation for the observed motions of celestial bodies. It could account for phenomena such as the retrograde motion of planets (the apparent backward motion of planets in the night sky) more effectively than the geocentric model.