heliocentric

Heliocentric refers to a model or perspective in which the Sun is treated as the center of the solar system or of a coordinate system. The word derives from the Greek helios, sun, and kentron, center. In the historical context of astronomy, a heliocentric model places the Sun near the middle and orbiting bodies—the planets, including Earth—in predictable paths. This stands in contrast to geocentric models that place Earth at the center.

Aristarchus of Samos proposed a heliocentric model in the 3rd century BCE, but it had little support at the time. The idea was revived in the 16th century by Nicolaus Copernicus, whose De revolutionibus orbium coelestium argued for a Sun-centered system and helped shift scientific consensus. Observational evidence from Galileo Galilei, such as the phases of Venus and the moons of Jupiter, supported heliocentrism. Johannes Kepler refined the model by describing planetary orbits as ellipses with the Sun at one focus, and Isaac Newton provided the gravitational framework that explained why bodies orbit the Sun. The heliocentric view ultimately supplanted the Ptolemaic geocentric system and became the foundation of modern astronomy.

Today, heliocentric is also used as a technical term in astronomy to describe a reference frame or coordinate system anchored on the Sun, such as heliocentric ecliptic coordinates. It underpins orbital calculations, spaceflight planning, and the interpretation of planetary motions. The term remains a key historical marker for the shift from Earth-centered to Sun-centered views of the cosmos.