| Astrophysics (Index) | About |
A heliocentric system is a model of the universe that assumes heliocentricity (Sun-centered, or heliocentric), i.e., that the planets orbit the Sun. This type of model displaced geocentric systems, i.e., in which the planets, stars, and Sun orbit the Earth. Geocentric systems such as the ancient homocentric-sphere models explained motions in the sky using the rotations of nested interconnected invisible spheres centered on Earth.
A heliocentric system offers a more straightforward means of calculating the apparent motion of planets in the celestial sphere. It presumes some planets closer to the Sun than Earth (termed inferior planets) and some further (superior planets). The inferior planets showed a maximum angle from the Sun (elongation) and the superior planets would reach an angle of 180° from the Sun (conjunction).
Current usage of the term heliocentric system (and heliocentrism, acceptance of such a system) varies regarding whether it means the Sun is the center of the entire universe, versus merely that the planets orbit around Sun. Historically, both Sun-centered models and models positing "many suns" (the other suns being what we see as stars) were proposed by ancient Greeks, though the Greeks' generally-accepted model was geocentric.