History of the center of the Universe Sun at the center of our Solar System. The word comes from the Greek ( "helios" "sun" and "kentron" "center"). The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BCE by Aristarchus of Samos, but had received no support from most other ancient astronomers. Nicolaus Copernicus' major theory of a heliocentric model was published in "De revolutionibus orbium coelestium" ("On the Revolutions of the Celestial Spheres"), in 1543, the year of his death, though he had formulated the theory several decades earlier. Copernicus' ideas were not immediately accepted, but they did
Age of the Earth it would take for the near-surface to cool to its present temperature. His calculations did not account for heat produced via radioactive decay (a process then unknown to science) or, more significantly, convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface. Even more constraining were Kelvin's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Kelvin estimated that the Sun is about 20 million years old. Geologists such as Charles Lyell