There isn't a single "solar theory" that was published in a specific year. The idea of the Sun being the center of our solar system, called heliocentrism, has evolved over centuries with contributions from various scientists and thinkers.

Here's a brief timeline of key developments:

* Ancient Greece (3rd Century BC): Aristarchus of Samos proposed a heliocentric model, but it was not widely accepted.

* 1543: Nicolaus Copernicus published "De Revolutionibus Orbium Coelestium" (On the Revolutions of the Heavenly Spheres), which revived the heliocentric model and provided strong arguments for it.

* 1609-1619: Johannes Kepler developed his laws of planetary motion, which provided accurate mathematical descriptions of planetary orbits around the Sun.

* 1687: Isaac Newton published "Philosophiæ Naturalis Principia Mathematica," which provided the physical laws of motion and gravity that explained why planets orbit the Sun.

Therefore, it's inaccurate to talk about a specific year when "solar theory" was published. Instead, the development of our understanding of the solar system has been a gradual process over many centuries.