It's difficult to pinpoint a single date when the Earth-centered solar system was *thought* to be a sun-centered system. The transition from geocentrism to heliocentrism was a gradual process that unfolded over centuries.

Here's a timeline of key moments:

* Ancient Greece (c. 3rd Century BC): Aristarchus of Samos proposed a heliocentric model, but it was largely rejected due to lack of observational evidence and the powerful influence of Aristotle's geocentric model.

* Medieval Period: The geocentric model, as described by Ptolemy in his book "Almagest," became the dominant view in Europe, supported by the Church.

* 16th Century: Nicolaus Copernicus revived the heliocentric model in his book "De Revolutionibus Orbium Coelestium" (1543). This work was controversial but laid the groundwork for a shift in thinking.

* 17th Century: Galileo Galilei's observations with his telescope (early 1600s) provided crucial evidence supporting heliocentrism, such as the phases of Venus, which were incompatible with a geocentric model. Johannes Kepler's laws of planetary motion (early 1600s) provided a mathematical framework for understanding the solar system.

Therefore, while Copernicus' book in 1543 was a significant turning point, it was not a definitive "date" for the switch to heliocentrism. The transition was a long process, taking centuries and involving many individuals' contributions.

It's important to note that even after the heliocentric model gained acceptance, some clung to geocentrism for religious or philosophical reasons. The transition from geocentric to heliocentric wasn't simply about one date but a complex process of scientific discovery, debate, and gradual acceptance.